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Hypotension during Anesthesia in Dogs and Cats: Recognition, Causes, and Treatment
Abstract
Perianesthetic hypotension is common in veterinary patients. The pathophysiology of hypotension is multifactorial but includes effects of injectable and inhalant anesthetic agents on the cardiovascular system. Hypotension can result in decreased perfusion to vital organs such as the brain, heart, and kidneys, leading to dysfunction. Direct and indirect methods of arterial blood pressure monitoring are available to veterinary practitioners. Continuous or frequent perianesthetic blood pressure monitoring allows quick recognition of hypotension and treatment of its underlying cause before negative consequences can occur. Treatment of hypotension may include decreasing anesthetic depth and administering intravenous crystalloid and colloid fluids, anticholinergic agents (as positive chronotropes), and positive inotropic agents to improve contractility. All these help to improve cardiac output and tissue perfusion, thereby preventing organ damage.
... (9) Con la disponibilità di metodi non invasivi a basso costo, la misurazione della PA deve sempre essere parte della routine di procedure chirurgiche in medicina veterinaria di piccoli animali, fattore che continua a essere una discriminante nella prevenzione della mortalità. (1,5,9) ...
... Il più delle volte l'ipotensione è dovuta a effetti collaterali da farmaci, nella fattispecie da xilazina, isoflurano, butorfanolo e acepromazina nei cani e diazepam e butorfanolo nei gatti, che influiscono direttamente sulla FC, sul precarico e postcarico, sulla CC, sulla RVP e indirettamente sulla DC e la PA. (5,9) Gli anestetici generali devono promuovere al contempo la SUMMARY Hypotension during anesthesia in dogs and cats Hypotension is considered one of the most common perianestetic complications in veterinary patients. This clinical condition is pressure so low it causes symptoms or signs due to the low flow of blood through the arteries and veins. ...
... Hypotension -blood pressure -anesthesia -perioperative privazione di stimoli chirurgici aggressivi e il rilassamento muscolare, con adeguata perfusione tissutale e traferimento di O2 dal corpo. (9) Il sovradosaggio anestetico provoca diminuzione della PA e bradicardia, mentre il sottodosaggio anestetico causa dolore e conseguente aumento di PA e tachicardia. L'iperinfusione provoca aumento della PA e bradicardia. ...
Hypotension is considered one of the most common perianestetic complications in veterinary patients. This clinical condition is pressure so low it causes symptoms or signs due to the low flow of blood through the arteries and veins. When the flow of blood is too low to deliver enough oxygen and nutrients to vital organs such as the brain, heart, bowel and kidney, the organs do not function normally and may be temporarily or permanently damaged. Monitoring of arterial blood pressure is a founda- mental key point of anesthesia management in small animal patients. Direct and indirect methods of arterial blood pressure measurement are routinely utilized to veterinarians. The continuous and meticulous surveillance of blood pressure allows quick recognition of hypotension and treatment of its underlying cause before negative consequences can appear. Treatment of hy- potension may include anesthetic depth changement, fluids (crystalloid and colloid) or drugs administering to improve cardiac contractility. All these help to improve cardiac output and tissue perfusion, thereby preventing organ damage
... ume have not been established. 3,4,[11][12][13] Importantly, there is little to no evidence that conventional volumes or rates of IV fluid administration are effective for the treatment of anesthetic-associated hypotension in dogs. To the contrary, experimental evidence suggests that conventional (10 to 30 mL/kg/h [4.5 to 13.6 mL/lb/h]) or higher (60 to 80 mL/kg/h [27.3 to 36.4 mL/lb/h]) rates of IV isotonic crystalloid solution administration are ineffective for treatment of isoflurane-associated hypotension in euvolemic dogs. ...
... Peer-reviewed manuscripts and current fluid therapy guidelines for dogs and cats recommend the equivalent of a fluid challenge as treatment for hypotension during anesthesia. 4,[11][12][13] The purpose of the study reported here was to determine the effects of rapid smallvolume fluid administration on arterial blood pressure measurements and associated hemodynamic variables in isoflurane-anesthetized euvolemic dogs with or without experimentally induced hypotension. We hypothesized that treatment with such a fluid-challenge equivalent would improve SAP in isoflurane-anesthetized nonhypotensive or hypotensive euvolemic dogs. ...
... Published reviews and guidelines for intraoperative fluid therapy suggest that crystalloid or colloid administration is effective for the treatment of hypotension during inhalation anesthesia. 4,5,[11][12][13] Recent evidence suggests that conventional rates or high volumes of isotonic crystalloid administration for the treatment of inhalation anestheticinduced hypotension (relative hypovolemia) are unlikely to result in substantial improvement in arterial blood pressure and that reducing the inhalation anesthetic concentration is key to its improvement. 14,15 However, conventional crystalloid fluid therapy can improve cardiac output during inhalation anesthesia in dogs. ...
Objective:
To determine the effects of rapid small-volume fluid administration on arterial blood pressure measurements and associated hemodynamic variables in isoflurane-anesthetized euvolemic dogs with or without experimentally induced hypotension.
Design:
Prospective, randomized, controlled study.
Animals:
13 healthy dogs.
Procedures:
Isoflurane-anesthetized dogs were randomly assigned to conditions of nonhypotension or hypotension (mean arterial blood pressure, 45 to 50 mm Hg) and treatment with lactated Ringer's solution (LRS) or hetastarch (3 or 10 mL/kg [1.4 or 4.5 mL/lb] dose in a 5-minute period or 3 mL/kg dose in a 1-minute period [4 or 5 dogs/treatment; ≥ 10-day interval between treatments]). Hemodynamic variables were recorded before and for up to 45 minutes after fluid administration.
Results:
IV administration of 10 mL/kg doses of LRS or hetastarch in a 5-minute period increased right atrial and pulmonary arterial pressures and cardiac output (CO) when dogs were nonhypotensive or hypotensive, compared with findings before fluid administration; durations of these effects were greater after hetastarch administration. Intravenous administration of 3 mL of hetastarch/kg in a 5-minute period resulted in an increase in CO when dogs were nonhypotensive. Intravenous administration of 3 mL/kg doses of LRS or hetastarch in a 1-minute period increased right atrial pressure and CO when dogs were nonhypotensive or hypotensive.
Conclusions and clinical relevance:
Administration of LRS or hetastarch (3 or 10 mL/kg dose in a 5-minute period or 3 mL/kg dose in a 1-minute period) improved CO in isoflurane-anesthetized euvolemic dogs with or without hypotension. Overall, arterial blood pressure measurements were a poor predictor of the hemodynamic response to fluid administration.
... Depressed myocardial function with decreased contractility and reduced cardiac output (CO) is observed together with vasodilation and decreased peripheral vascular resistance. The combination of decreased CO and vasodilation can lead to hypotension and may ultimately reduce organ perfusion (Mazzaferro and Wagner 2001). ...
... Therefore, a goal when using inhalant anesthetics should be to reduce the amount of gas needed to keep a patient anesthetized. The use of balanced anesthesia, combining opioid analgesic agents with decreased doses of inhaled anesthetics, can aid in maintaining adequate anesthetic depth without further depressing cardiovascular function (Mazzaferro et al 2001). ...
... At 1.2 MAC (or 1.6% isoflurane) the CO was 1.9 ± 0.1 L min -1 . Our higher CO values of 2.3 ± 0.7 L min -1 at a lower ET-Iso of 1.3% may be due to increased venous return or decreased afterload in our patients since inhalants are known to cause a dose-dependent cardiovascular depression (Page et al 1991; Mazzaferro and Wagner 2001). In one study, LiDCO was evaluated in healthy female dogs undergoing ovariohysterectomy in a clinical setting. ...
... Although it would appear that sAP is not consistently measured in anesthetized animals, hypotension is a common complication in veterinary anesthesia (Mazzaferro & Wagner 2001). In a prospective study where hypotension was defined as a systolic arterial pressure (SAP) <80 mmHg or mean arterial pressure (MAP) <60 mmHg, hypotension occurred in 7% of 2556 anesthetized dogs and 8% of 683 anesthetized cats (Gaynor et al. 1999). ...
... A retrospective study recorded hypotension in 71% of diabetic and 63% of non diabetic dogs undergoing general anaesthesia for phacoemulsification surgery (Oliver et al. 2010). Intra-operative sAP measurement and management of hypotension have been associated with improved outcome and reduced complications (Mazzaferro & Wagner 2001;Monk et al. 2005). ...
... Hypotension is the most common complication during general anesthesia (Gaynor et al. 1999;Bidwell et al. 2007;Brodbelt et al. 2008a;Vetoquinol 2009). Intra-operative and post-operative problems have been described as sequelae in human and veterinary medicine, including prolonged recovery, organ failure, neurological deficits and myopathies (Trojaborg & Boysen 1973;Pasch & Huk 1986;Mazzaferro & Wagner 2001;Bidwell et al. 2007;Papadonikolakis et al. 2008). While hypotension can be a problem, it must be appreciated that pressure is the product of resistance and flow. ...
Objective
Determine arterial blood pressure range that diplomates of the American College of Veterinary Anesthesia and Analgesia (ACVAA) and European College of Veterinary Anaesthesia and Analgesia (ECVAA) use to define intraoperative hypotension in dogs and identify the threshold values used for intervention.Study designSurvey of veterinary anesthesia specialists.PopulationDiplomates of the ACVAA and ECVAA.MethodsACVAA and ECVAA diplomates (n = 313) were invited to participate in an Internet-based survey regarding anesthetized healthy dogs undergoing two types of procedures (diagnostic or surgical).ResultsThere were 151 respondents to the survey; 70.2% were ACVAA diplomates and 29.8% were ECVAA diplomates. The majority of the respondents (70.9%) worked in academia while the others were in private practice (19.2%), or research, diagnostic or pharmaceutical fields (9.9%). Hypotension was defined (mean ± SD) by the respondents as systolic arterial blood pressure (SAP) <87 ± 8 mmHg for surgical cases and <87 ± 6 mmHg for diagnostic cases, or mean arterial pressure (MAP) <62 ± 4 mmHg for both types of cases. Arterial pressures reported to prompt treatment were SAP 85 ± 13 mmHg or MAP 61 ± 4 mmHg in surgical cases, and SAP 84 ± 11 mmHg or MAP 63 ± 8 mmHg in diagnostic cases.Conclusions and clinical relevanceThere was agreement between ACVAA and ECVAA diplomates on the definition of intraoperative hypotension in dogs during anesthesia. The blood pressures used to define hypotension were similar to the pressures that would prompt diplomates to start treatment. Readers could infer that diplomates define hypotension as a clinical condition that requires treatment at the time of diagnosis.
... At our veterinary teaching hospital it is seen in 21 and 36% of ASA I and II cases, respectively (Chen et al. 2007). Hypotension is defined as a mean arterial pressure (MAP) <60 mmHg, corresponding to a systolic arterial pressure (SAP) <80-90 mmHg (Mazzaferro & Wagner 2001). The pathophysiology of hypotension is multifactorial, but pre-anesthetic management as well as the effects of anesthetic drug regimes on the cardiovascular system can be partly responsible. ...
... Intravenous crystalloid fluid administration (approximately 20 mL kg )1 ) given as a bolus is suggested to increase the circulating fluid volume and compensate for vasodilation and depressed contractility caused by anesthetic agents (Mazzaferro & Wagner 2001). These volumes are based on the estimated pre-anesthetic fluid losses (<5%) expected in patients. ...
... A crystalloid fluid bolus of lactated Ringer's solution of 10-20 mL kg )1 has been used clinically and some veterinary literature suggests this as an option to treat hypotension during inhalational anesthesia (Mazzaferro & Wagner 2001;Wagner & Hellyer 2002). A crystalloid fluid bolus increases venous return and therefore CO. ...
Objective To determine the impact of acepromazine on the cardiovascular responses to three treatments for hypotension in dogs during deep isoflurane anesthesia.
Study design Prospective blinded randomized cross-over experimental design.
Animals Six adult (2.5 ± 0.5 year old) healthy mixed breed dogs (24.2 ± 7.6 kg).
Methods Anesthesia was induced with propofol (4–6 mg kg−1, IV) and maintained with isoflurane. Each dog received six treatments separated by at least 5 days. Once instrumented, dogs randomly received acepromazine (0.05 mg kg−1) (Ace) or saline (equal volume) (Sal) IV and end-tidal isoflurane (E′Iso) was adjusted to achieve hypotension, defined as a mean blood pressure between 45 and 50 mmHg. Dogs randomly received dextran (D) (7 mL kg−1) or lactated Ringer’s (LR) (20 mL kg−1) over 14 minutes, or ephedrine (Eph) (0.1 mg kg−1 followed by 10 μg kg−1 minute−1) throughout the study. Measurements were taken at baseline, 5, 10, 15, 20, 30, and 40 minutes. Data were analyzed with a Latin Square in two factors (Ace/Sal and treatment) for repeated measures, with further comparisons if appropriate (p < 0.05).
Results E′Iso producing hypotension was significantly less following Ace (2.07 ± 0.23%) than Sal (2.43 ± 0.23%). No improvement in cardiac output (CO) was observed with D or LR. LR initially intensified hypotension with a significant reduction in SVR, while D caused a minor improvement in ABP. Eph produced a significant increase in ABP, CO, hemoglobin, oxygen content and delivery. Pre-treatment with Ace minimized ABP improvements with all treatments.
Conclusions and clinical relevance Acepromazine (0.05 mg kg−1 IV) enhanced the hypotensive effect of isoflurane, although it maintained CO. Administration of LR significantly worsens ABP initially by further vasodilation. D caused minimal improvement in ABP. At the infusion studied, Eph effectively countered the cardiovascular depression produced by deep isoflurane anesthesia, but extremes in ABP associated with initial vasoconstriction prevent our recommendation at this dose.
... Moreover, virtually all anaesthetic drugs cause hemodynamic disturbances. A persistent complication associated with the pharmacodynamic properties of anaesthetics is a drop in cardiac output (CO), leading to decreased blood pressure and reduced tissue perfusion, with potentially fatal consequences [3][4][5]. In addition, during severe inflammatory and infectious diseases, which often lead senior dogs to the operating room, the myocardial contractile function may be reduced as well [6]. ...
... As these catecholamines have a short half-life, they must be administered through continuous infusion using pumps or syringe pumps. This process adds to the complexity and cost of anaesthetic [4,[7][8][9]. ...
Simple Summary
Pimobendan is a drug that improves cardiac output and contractility in dogs with mitral valve disease and dilated cardiomyopathy, as well as in healthy adult dogs. The intravenous injectable formulation has shown immediate cardiovascular effects in dogs without pro-arrhythmogenic effects. Our study aims to assess the haemodynamic effects of the intravenous administration of pimobendan at a dose of 0.15 mg/kg intravenously in healthy senior dogs undergoing general anaesthesia for surgical procedures. The results of this study showed that pimobendan improves cardiac function parameters measured with an oesophageal Doppler monitor in senior dogs with no previous heart disease. Pimobendan could be used during general anaesthesia in senior dogs when there is concern about the possible presence of impaired cardiac function. There were no significant changes in blood pressure or heart rate. In the present study, continuous haemodynamic monitoring showed that the effects appeared from the first minute and continued for at least 20 min.
Abstract
Pimobendan is an inotropic and vasodilator drug with no sympathomimetic effects. This study aimed to evaluate the haemodynamic effects of pimobendan during anaesthesia in healthy senior dogs. A prospective, randomised, triple-blinded, placebo-controlled clinical study was conducted. Thirty-three dogs (median [range]: 9 [7, 12] years) were anaesthetised for surgical procedures. The dogs were randomly allocated into two groups: eighteen dogs received intravenous pimobendan at a dose of 0.15 mg/kg (PIMOBENDAN), and fifteen dogs received intravenous saline solutions at a dose of 0.2 mL/kg (PLACEBO). Data were recorded before, 1 min, 10 min, and 20 min after injection. Velocity-time integral (VTI), peak-velocity (PV), and mean-acceleration (MA) were measured using an oesophageal Doppler monitor (ODM). Heart rate and mean arterial pressure were also registered. The data were analysed using a two-way ANOVA for trimmed means. Statistical differences were considered if p < 0.05. Twenty minutes after injection, the VTI (13.0 cm [10.4, 22.3]), PV (95.0 [83.0, 160] m/s), and MA (12.6 [9.40, 17.0] m/s²) were significantly higher in the PIMOBENDAN group compared to the PLACEBO group (VTI: 10.5 [6.50, 17.4] cm, PV: 80.0 [62.0, 103] m/s and MA: 10.2 [7.00, 16.0] ms²). No significant differences were observed in the rest of the variables. Using pimobendan during anaesthesia increases VTI, PV, and MA, as measured by an ODM.
... On the other hand, virtually all anaesthetic drugs cause hemodynamic disturbances. A persistent complication associated with the pharmacodynamic properties of anaesthetics is a drop in cardiac output (CO), leading to decreased blood pressure and reduced tissue perfusion, with potentially fatal consequences [3][4][5]. ...
... As these catecholamines have a short half-life, they must be administered through continuous infusion using pumps or syringe pumps. This process adds to the complexity and cost of anaesthetic [4,[6][7][8]. ...
Pimobendan is an inotropic and vasodilator drug with no sympathomimetic effects. This study aimed to evaluate the haemodynamic effects of pimobendan during anaesthesia in healthy senior dogs. A prospective, randomised, triple-blinded, placebo-controlled clinical study was conducted. Thirty-three dogs (median [range]: 9 [7, 12] years) were anaesthetised for surgical procedures. Dogs were randomly allocated into two groups: eighteen dogs received pimobendan 0.15 mg kg-1 IV (PIMOBENDAN) and 15, saline solutions 0.2 ml kg-1 IV (PLACEBO). Data were recorded before, 1 minute, 10 minutes and 20 minutes after injection. Velocity-time integral (VTI), peak-velocity (PV) and mean-acceleration (MA) were measured using an oesophageal Doppler monitor (ODM). Heart rate and mean arterial pressure were also registered. Data were analysed using a two-way ANOVA for trimmed means. Statistical differences were considered if p < 0.05. Twenty minutes after injection, VTI (13.0 cm [10.4, 22.3]), PV (95.0 [83.0, 160] m sec-1), and MA (12.6 [9.40, 17.0] m sec-2) were higher in PIMOBENDAN when compared to PLACEBO (VTI: 10.5 [6.50, 17.4] cm, PV: 80.0 [62.0, 103] m sec-1 and MA: 10.2 [7.00, 16.0] m sec-2). No differences were observed in the rest of the variables. Using pimobendan during anaesthesia increases VTI, PV and MA measured by an ODM.
... Even though oxygen was provided, our patient was suspected to be suffering from etorphine-induced hypoxaemia and acidosis, which likely resulted in poor cardiovascular performance and vasodilation. Additional inflammatory mediated vasodilation together with the hypovolaemic status of the dehydrated animal likely caused the profound hypotension [5,33,34]. Stimulation of afferent and efferent pathways in the vagus nerve, resulting from manipulation of the caudal pharyngeal region, may have contributed to the low BP [33]. ...
... Dobutamine and phenylephrine infusions have been used to maintain mean arterial BP in white and black rhinoceroses anaesthetised with isoflurane in oxygen [7,10]. However, the inotropic and chronotropic effects of dobutamine lead to an increase in myocardial oxygen demand and may have been harmful in a rhinoceros that suffered from etorphine-induced hypoxaemia associated with poor myocardial oxygenation [33,34]. The potent vasoconstrictor phenylephrine in contrast is known to impair peripheral oxygen delivery and skeletal muscle blood flow [35]. ...
A subadult white rhinoceros bull presented for oesophageal endoscopic evaluation and foreign body removal under general anaesthesia. The animal had a history of nasal and oral regurgitation of water and ingesta with weight-loss for 6 days prior to the procedure and had been diagnosed with oesophageal obstruction caused by a bailing wire. Anaesthesia was induced with intramuscular etorphine and azaperone delivered remotely by dart, followed by an intravenous bolus of ketamine. The trachea was intubated, and anaesthesia was maintained with an etorphine-ketamine constant rate infusion (CRI). The rhinoceros did not respond predictably to induction of anaesthesia and developed life-threatening systemic hypotension throughout the 90-minute procedure. A mega-vertebrate demand ventilator was successfully used to provide intermittent positive pressure ventilation when the rhinoceros developed apnoea. This case report describes the maintenance of anaesthesia of a white rhinoceros using an etorphine-ketamine CRI and the causes and management of hypotension and respiratory impairment observed in this patient.
... This condition can lead to cellular hypoxia and ischemic injury to vital organs, as well as an increase in morbidity and mortality rates [7]. Consequently, the early recognition of this condition is crucial for implementing therapeutic interventions to restore normal hemodynamic function [8]. ...
Blood pressure (BP) monitoring is essential during anesthesia to maintain cardiovascular stability and detect hypotension. This study evaluated the agreement and diagnostic accuracy of linear deflection oscillometry (LDO) and Doppler compared to invasive blood pressure (IBP) in anesthetized dogs. Eleven healthy dogs were anesthetized, and BP measurements were taken using LDO, Doppler, and IBP methods under normotensive and hypotensive conditions. The LDO device demonstrated superior agreement, assessed using Bland–Altman analysis, with IBP, especially in hypotensive conditions, compared to the Doppler method. LDO showed bias and standard deviation in the hypotensive state, with a mean and systolic arterial pressure (MAP and SAP) of −5.1 ± 7.9 and −5.6 ± 12.5 mmHg, respectively. Conversely, Doppler measurements tended to overestimate SAP during hypotension, presenting a bias of −13 ± 15.45 mmHg. The LDO achieved an area under the curve (AUC) of 0.809 for hypotension detection, with an MAP cutoff of ≤72 mmHg (sensitivity: 90%, specificity: 63%). Meanwhile, the best threshold for Doppler measurements was an AUC of 0.798, SAP ≤ 100 mmHg (sensitivity: 77.8%, specificity: 81.8%). These results indicate that LDO is a reliable method for hypotension detection in anesthetized dogs, with potential applications for real-time monitoring. In contrast, the Doppler method may help confirm hypotension diagnoses.
... 13,18 Although there is limited evidence about the effect of intraoperative hypotension on postoperative adverse outcomes in dogs, its prompt treatment is considered mandatory 29,30 and when established it has been associated with improved outcome and reduced complications. 31 A recent review in human medicine showed that even a few minutes of mild intraoperative hypotension was associated with organ injury. 32 This damage would increase with prolonged exposure and with more marked hypotension. ...
A 3-year-old, male neutered, 2.7 kg Chihuahua was referred for correction of a type IIA, left-to-right shunting PDA. The correction of the PDA required two separate interventions. During the first intervention, a minimally invasive transvascular correction of the PDA that was converted to a thoracotomy was suspended after the evidence of iatrogenic haemopericardium. The second intervention, scheduled after the resolution of the haemopericardium, consisted of surgical ligation of the PDA via thoracotomy. Long periods of hypotension (mean arterial pressure below 60 mm Hg) were observed during the first intervention, during which anaesthesia was maintained with a combination of sevoflurane and infusions of fentanyl and lidocaine. The use of total intravenous anaesthesia with alfaxalone in conjunction with locoregional techniques in the second intervention provided smooth anaesthesia with improved cardiovascular stability. K E Y WO R D S alfaxalone, anaesthesia, anaesthetic management, cardiovascular disease, dog, patent ductus arteriosus BACKGROUND
... No presente estudo, independentemente da faixa de peso (Grupos 1 e 2), o valor do viés foi ligeiramente negativo para a PAM. Os valores de viés negativos possuem uma relevância clínica bastante importante, pois havendo superestimação do valor de pressão, pode-se deixar de tratar um animal hipotenso, trazendo consequências graves como diminuição da perfusão de órgãos vitais levando a sua disfunção [7]. Em estudo realizado anteriormente [9], utilizando oito cães com peso de 19 a 32 kg, a concordância do monitor oscilométrico PetMap foi avaliada em normotensão e hipotensão (PAM ~ 40 mmHg) induzida pela retirada de aproximadamente 40% do volume sanguíneo. ...
Background: Arterial blood pressure is one of the most commonly variables monitored during anesthetic procedures in veterinary patients. The most reliable method for measuring arterial blood pressure in dogs and cats is the direct (invasive) method. However, the oscillometric method is less complex and more practical for clinical routine in small animals. Nevertheless, oscillometric monitors present great variability in accuracy. The present study aimed to determine the accuracy of the Delta Life DL 1000 oscillometric monitor for measurement of systolic, mean and diastolic blood pressures (SAP, MAP and DAP, respectively) in anesthetized dogs of different weight ranges.Materials, Methods & Results: This study was approved by the Institutional Ethics Committee of Animal Use. Fifteen female dogs of different breeds, weighing 11.6 ± 10.0 kg and with a mean age of 48 ± 51 months were used. All animals were scheduled for elective surgery under general anesthesia in the Institution Veterinary Hospital. Dogs were anesthetized with morphine, propofol and isoflurane and had one 20 or 22 gauge catheter introduced into the dorsal pedal artery for continuous, invasive monitoring of SAP, MAP and DAP. A blood pressure cuff was positioned over the middle third of the radius and connected to Delta Life DL 1000 monitor. Oscillometric readings of SAP, MAP and DAP were registered every 5 minutes, and invasive values were simultaneously recorded. Values obtained with both methods were compared (invasive versus oscillometric) by use of the Bland Altman method to determine the bias, standard deviation of bias and 95% limits of agreement. The percentages of errors between the methods within 10 mmHg and within 20 mmHg were calculated. The results obtained were compared with the criteria from the American College of Veterinary Internal Medicine (ACVIM) for validation of indirect methods of arterial blood pressure measurement. Data were stratified into two groups according to the weight: < 10 kg (Group 1; n = 9); and ≥ 10 kg (Group 2; n = 6). In Group 1, 119 paired measurements were obtained, four of which classified as hypotension (SAP < 90 mmHg), 98 as normotension (SAP from 90 to 140mmHg) and 17 as hypertension (SAP > 140 mmHg). Bias (± SD) values in Group 1 were as follows: SAP, 5.2 ± 18.1 mmHg; MAP, -3.4 ± 17.2 mmHg; and DAP, 12.0 ± 17.5 mmHg. The percentages of errors within 10 mmHg were 40.3% for SAP; 45.4% for MAP and 28.6% for DAP. The percentages of errors within 20 mmHg were 72.3% for SAP, 84.0% for MAP and 68.1% for DAP. In Group 2, 66 paired measurements were obtained, nine of which classified as hypotension, 56 as normotension and one as hypertension. Bias (± SD) in Group 2 were as follows: SAP, 13.6 ± 14.3 mmHg; MAP, -1.1 ± 13.5 mmHg; and DAP, 8.2 ± 16.0 mmHg. The percentages of errors within 10 mmHg were 33.3% for SAP, 77.3% for MAP and 33.3% for DAP. The percentages of errors within 20 mmHg were 65.1% for SAP, 92.4% for MAP and 83.4% for DAP.Discussion: Based on the results of this study and reference criteria from the ACVIM, the Delta Life DL 1000 monitor had a poor accuracy for SAP, MAP and DAP and did not meet the criteria from the ACVIM in anesthetized dogs under 10 kg. Measurements of MAP in dogs ≥ 10 kg met the ACVIM criteria, but measurements of SAP and DAP did not. Based on the findings in this study, the DL 1000 oscillometric monitor is not recommended for blood pressure measurement in anesthetized dogs < 10 kg. In dogs ≥ 10 kg, measurements of MAP yielded acceptable values, but SAP and DAP measurements did not.
... However, hypotension that is caused by vasodilation (relative hypovolemia) from anesthetic drugs has an unpredictable responsiveness to fluid therapy [29,30]. A fluid challenge with crystalloid fluids is recommended in an effort to assess fluid responsiveness in hypotensive dogs under general anesthesia [28,[31][32][33]. For this study, fluid treatment for hypotension followed the American Animal Hospital Association (AAHA) Guidelines for fluid therapy for dogs and cats [22]. ...
Objective
To evaluate the effects of intravenous maropitant on arterial blood pressure in healthy dogs while awake and under general anesthesia.
Design
Experimental crossover study.
Animals
Eight healthy adult Beagle dogs.
Procedure
All dogs received maropitant (1 mg kg⁻¹) intravenously under the following conditions: 1) awake with non-invasive blood pressure monitoring (AwNIBP), 2) awake with invasive blood pressure monitoring (AwIBP), 3) premedication with acepromazine (0.005 mg kg⁻¹) and butorphanol (0.2 mg kg⁻¹) intramuscularly followed by propofol induction and isoflurane anesthesia (GaAB), and 4) premedication with dexmedetomidine (0.005 mg kg⁻¹) and butorphanol (0.2 mg kg⁻¹) intramuscularly followed by propofol induction and isoflurane anesthesia (GaDB). Heart rate (HR), systolic (SAP), diastolic (DAP), and mean blood pressures (MAP) were recorded before injection of maropitant (baseline), during the first 60 seconds of injection, during the second 60 seconds of injection, at the completion of injection and every 2 minutes post injection for 18 minutes. The data were compared over time using a Generalized Linear Model with mixed effects and then with simple effect comparison with Bonferroni adjustments (p <0.05).
Results
There were significant decreases from baseline in SAP in the GaAB group (p < 0.01) and in MAP and DAP in the AwIBP and GaAB (p < 0.001) groups during injection. A significant decrease in SAP (p < 0.05), DAP (p < 0.05), and MAP (p < 0.05) occurred at 16 minutes post injection in GaDB group. There was also a significant increase in HR in the AwIBP group (p < 0.01) during injection. Clinically significant hypotension occurred in the GaAB group with a mean MAP at 54 ± 6 mmHg during injection.
Conclusion
Intravenous maropitant administration significantly decreases arterial blood pressure during inhalant anesthesia. Patients premedicated with acepromazine prior to isoflurane anesthesia may develop clinically significant hypotension.
... Recall from Chapter 40 that sinus bradycardia may result from the following [1,[8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]: ...
To maintain a steady state, homeostasis, the body tightly regulates physiological processes, including heart rate. Heart rate is the function of two opposing pathways, the sympathetic and parasympathetic nervous system, working in sync to coordinate the cardiac cycle. When heart rate drops below the reference range for what is considered normal, dogs and cats are said to be bradycardic. Bradycardia may result from cardiac or systemic dysfunction. Conditions that result in cardiac dysfunction were described in Chapter 40. This chapter emphasizes systemic disturbances that lead to bradycardia, including electrolyte imbalances, high vagal tone, and hypothermia. In addition, bradycardia may result from the administration of select anesthetic and analgesic agents.
... 14 Anesthetic-induced hypotension is commonly associated with relative hypovolemia (vasodilatation) attributable to the vasodilatative effects of anesthetic drugs (particularly inhalation anesthetics) and suppression of compensatory homeostatic mechanisms. Hypotension during anesthesia has been associated with a higher mortality rate in dogs and cats, [15][16][17] which further indicates the importance of monitoring and prompt treatment of this condition. In the present study, hypotension was induced by increasing the concentration of isoflurane, and blood pressure was increased by administration of dobutamine. ...
OBJECTIVE To investigate use of the plethysmographic variability index (PVI) and perfusion index (PI) for evaluating changes in arterial blood pressure in anesthetized tigers ( Panthera tigris ).
ANIMALS 8 adult tigers.
PROCEDURES Each tiger was anesthetized once with a combination of ketamine, midazolam, medetomidine, and isoflurane. Anesthetic monitoring included assessment of PI, PVI, direct blood pressure measurements, anesthetic gas concentrations, esophageal temperature, and results of capnography and ECG. Mean arterial blood pressure (MAP) was maintained for at least 20 minutes at each of the following blood pressure conditions: hypotensive (MAP = 50 ± 5 mm Hg), normotensive (MAP = 70 ± 5 mm Hg), and hypertensive (MAP = 90 ± 5 mm Hg). Arterial blood gas analysis was performed at the beginning of anesthesia and at each blood pressure condition.
RESULTS Mean ± SD PI values were 1.82 ± 2.38%, 1.17 ± 0.77%, and 1.71 ± 1.51% and mean PVI values were 16.00 ± 5.07%, 10.44 ± 3.55%, and 8.17 ± 3.49% for hypotensive, normotensive, and hypertensive conditions, respectively. The PI values did not differ significantly among blood pressure conditions. The PVI value for the hypotensive condition differed significantly from values for the normotensive and hypertensive conditions. The PVI values were significantly correlated with MAP ( r = −0.657). The OR of hypotension to nonhypotension for PVI values ≥ 18% was 43.6.
CONCLUSIONS AND CLINICAL RELEVANCE PVI was a clinically applicable variable determined by use of noninvasive methods in anesthetized tigers. Values of PVI ≥ 18% may indicate hypotension.
... To decrease the likelihood of movement, rhinoscopy patients are often maintained at a deep plane of anesthesia, which causes dose-dependent cardiorespiratory depression that can lead to hypotension and apnea. [2][3][4][5] Use of multimodal anesthesia, including local anesthetics for a local or regional nerve block, may help to decrease the amount of inhalation anesthetics required, thereby decreasing the severity of complications associated with a deep plane of anesthesia. [6][7][8][9] Providing regional antinociception to the nasal cavity and corresponding structures is challenging because of the complexity of innervation to the face and nose. ...
OBJECTIVE To determine whether a maxillary nerve block via a modified infraorbital approach, applied before rhinoscopy and nasal biopsy of dogs, would decrease procedural nociception, minimize cardiorespiratory anesthetic effects, and improve recovery quality.
ANIMALS 8 healthy adult hound-type dogs
PROCEDURES In a crossover study, dogs received 0.5% bupivacaine (0.1 mL/kg) or an equivalent volume of saline (0.9% NaCl) solution as a maxillary nerve block via a modified infraorbital approach. A 5-cm, 20-gauge over-the-needle catheter was placed retrograde within each infraorbital canal, and bupivacaine or saline solution was administered into each pterygopalatine region. Rhinoscopy and nasal biopsy were performed. Variables monitored included heart rate, systolic arterial blood pressure (SAP), mean arterial blood pressure (MAP), diastolic arterial blood pressure (DAP), plasma cortisol and norepinephrine concentrations, purposeful movement, and pain scores. After a 14-day washout period, the other treatment was administered on the contralateral side, and rhinoscopy and nasal biopsy were repeated.
RESULTS SAP, MAP, and DAP were significantly higher for the saline solution treatment than for the bupivacaine treatment, irrespective of the time point. Plasma cortisol concentrations after saline solution treatment were significantly higher 5 minutes after nasal biopsy than at biopsy. Heart rate, norepinephrine concentration, purposeful movement, and pain score were not significantly different between treatments.
CONCLUSIONS AND CLINICAL RELEVANCE Maxillary nerve block via a modified infraorbital approach prior to rhinoscopy and nasal biopsy reduced procedural nociception as determined on the basis of blood pressures and plasma cortisol concentrations during anesthesia. These findings warrant further evaluation in dogs with nasal disease.
... Although TEE has been mainly used as an assistant tool for catheter intervention in veterinary medicine [23,30,33,35], few reports on the intraoperative cardiac evaluation are available in dogs with heart failure. To enhance anesthetic safety, intraoperative blood pressure has been monitored by way of prevention of acute renal disorders and cerebral ischemia [21]. ...
The purpose of the present study is to investigate the effect of postural change on transesophageal echocardiography (TEE) views and parameters of interest anesthesia monitoring in healthy dogs. Twelve Beagle dogs were anesthetized and randomly positioned in one of four postures: right lateral-recumbency, left lateral-recumbency, supine position and prone position. After examinations in one posture, the same examination was demonstrated in another posture and repeated in all postures. In each posture, several standard TEE views were demonstrated: longitudinal cranial-esophageal aorta long-axis-view, transverse middle-esophageal mitral valve long-axis-view and transgastric middle short-axis-view. Additionally, echocardiographic parameters were attempted to measure, and direct blood pressure monitoring was performed in each view. As a result, oriented views, except for transgastric middle short-axis-view, could be obtained in all postures. Stroke volume and peak early diastolic velocity of mitral inflow were lower in supine position compared with those in right and left lateral-recumbency. Heart rate (HR) and systemic vascular resistance were higher in supine position compared with those in right and left lateral-recumbency. Left ventricular pre-ejection period/left ventricular ejection time corrected and uncorrected by HR were higher in supine position compared with those in right and left lateral-recumbency. In conclusion, longitudinal cranial-esophageal aorta long-axis-view and transverse middle-esophageal mitral valve long-axis-view provide useful information of interest anesthesia monitoring, because of their views enable to certainly obtain TEE parameters in various postures. Furthermore, TEE parameters allow to detect the changes of preload, afterload and HR that occur in supine position dogs.
... Intravenous crystalloid fluid solutions at a dose of 10 ml/kg/h should be given to alleviate anaesthesia-induced hypotension. Treatment of acute blood loss due to haemorrhage includes crystalloid fluid replacement at a dose of three times the blood volume lost [61][62][63] . If intraoperative anaesthesia is deeper than required, side effects resulting from hypotension and hypertension increase. ...
... Systemic mean arterial pressure , 65 mmHg is known to result in loss of perfusion auto regulation and subsequent myocardial, renal and cerebral ischemia (26,27). Severe intraoperative hypotension (systolic pressure , 65 mmHg) was documented in 78% of our dogs using indirect measurements via Doppler ultrasonography, and the incidence was not different between groups nor was it associated with increased frequency of post-operative complications or death. ...
This study evaluated the safety of preoperative computed tomography angiography (CTA) and its effect on surgical time and clinical outcomes in dogs that underwent surgical correction of a single congenital extrahepatic portosystemic shunt (CEPSS). Patient data were retrospectively collected from medical records and owner communications for 124 dogs with single CEPSS, undergoing preoperative CTA (n = 43) or not (n = 81) which were surgically treated from 2005 to 2014. The frequency of major postoperative complications was 4.7% and 9.9% for the CTA and no CTA groups, respectively (P = 0.49). Mean +/- standard deviation (SD) surgical time for the preoperative CTA group was 84 +/- 40 min and 81 +/- 31 min for the no CTA group (P = 0.28). We conclude that anesthetized preoperative CTA appears to be a safe method for diagnosis and surgical planning in dogs with single CEPSS, and does not appear to affect surgical procedure time, complication rate, or clinical outcome.
... A PAPm permaneceu sem variações, podendo-se afirmar que a redução da pressão arterial causada pelo butorfanol não foi capaz de interferir no trabalho cardíaco direito. Tais achados divergem daqueles observados na associação do opioide com a acepromazina, a qual resultou em diminuição acentuada da PAPm (17) , fato possivelmente relacionado à ação antiadrenérgica e vasodilatadora direta do fenotiazínico (17,18) . Quanto ao DC, houve decréscimo dos valores iniciais no GB, a partir de M45 até M75, de modo que, no momento final da avaliação, a média do GP foi maior que a do GB. ...
The aim of this study was to evaluate the hemodynamic effects of the total intravenous anesthesia with propofol and butorphanol in dogs. For that purpose, twenty adult healthy crossbred dogs were used. The animals were equally allocated into two groups (PG and BG) and induced to the anesthesia with intravenous propofol (10 mg/kg). After orotracheal intubation, controlled ventilation was instituted with 60% oxygen and flow of 30 mL/kg/min in a closed system, with controlled volume. The anesthetic maintenance was accomplished with propofol (0.6 mg/kg/min). The butorphanol group (BG) received, butorphanol 0.1 mg/kg IV, followed by continuous infusion (40 μg/kg/h). The placebo group (PG) received only NaCl 0.9% in bolus, followed by venous infusion, in identical volume of the BG. Baseline hemodynamic measurements were performed before opioid or saline administration (M0) and immediately after, every 15 minutes (M15 to M75). Administration of butorphanol resulted in decrease of total peripheric resistance (TPR), arterial pressures (SAP, DAP, MAP) and cardiac output (CO), without clinical relevance. The results allow us to conclude that association provides safe anesthesia for patients with ventilatory support.
... Therefore, drugs with minimal depressant effect should be importantly usedin low doses and in combination. Diazepam cause minimal cardiovascular depression, rarely cause hypotension, provides some narcosis, good muscle relaxation and no analgesia [36]. While ketamine as a sole anesthetic agent in critical ill patient has a direct depressant effects resulting in poor contractility, decreased cardiac output and respiratory depression [31,34]. ...
This study aimed to evaluate, diagnosis and management of series cases in cats suffered from some
critical urogenital problems causing abdominal pain. Forty-seven cats (21 Shiraz, 22 Siamese and 4 Egyptian
Mau) were included. Diagnosis was based on history, clinical signs, cardiovascular and respiratory monitoring,
radiography, abdominal ultrasonography, hematological and biochemical analysis. Feline Urologic Syndrome
(FUS) was diagnosed in 18/47 cats (38.3%); urinary bladder rupture (UBR) 2/47 (4.3%); polycystic kidney (PKD)
1/47 (2.1%); uterine rupture (UtR) 1/47 (2.1%) and closed cervix pyometra (CP) 25/47 (53.2%). Cats were
subjected to resuscitation and medical management before surgical intervention. Animals suffered FUS were
treated using retrograde urohydropropulsion with cystocentesis and/ or tube cystostomy with successful
recovery. Percutenous cystic aspiration was performed in the case of PKD. Ovariohystrectomy was the
radical treatment in cats suffered from both CP and UtR. Cats with UBR were treated with cystorrhaphy.
Results revealed successful recovery and good outcome inspite a case of FUS was died before treatment..
In conclusion, tube cystostomy is a successful method for treatment of refractory cases of obstructed FUS.
Hyperkalemia and azotemia should be considered in cats suffering FUS, uroabdomen and PKD. Relevance rapid
resuscitation, prompt diagnosis and accurate treatment are the corner stone for management of critical
urogenital disorders causing abdominal pain.
... 5 Balanced or multimodal anesthesia, in which concurrent administration of analgesic agents allows the amount of inhalant anesthetic administered to be decreased while still maintaining an adequate surgical plane of anesthesia, can decrease the severity of cardiovascular depression in anesthetized dogs, compared with the administration of the inhalant anesthetic alone. 6 The MAC is the lowest alveolar concentration of an inhalant anesthetic that prevents gross purposeful movement in response to a noxious stimulus in 50% of animals, and the MAC of isoflurane has been established for dogs and cats. 7 Results of multiple studies [8][9][10][11][12] indicate that administration of 1 or more analgesics, including opioids, α 2 -adrenoceptor agonists, Nmethyl-D-aspartate receptor antagonists, and lidocaine, can reduce the MAC of various inhalant anesthetics required for a surgical plane of anesthesia and thereby reduce cardiorespiratory depression and the risk of anesthetic complications. ...
Objective:
To determine the effect of dexmedetomidine, morphine-lidocaine-ketamine (MLK), and dexmedetomidine-morphine-lidocaine-ketamine (DMLK) constant rate infusions on the minimum alveolar concentration (MAC) of isoflurane and bispectral index (BIS) in dogs.
Animals:
6 healthy adult dogs.
Procedures:
Each dog was anesthetized 4 times with a 7-day washout period between anesthetic episodes. During the first anesthetic episode, the MAC of isoflurane (baseline) was established. During the 3 subsequent anesthetic episodes, the MAC of isoflurane was determined following constant rate infusion of dexmedetomidine (0.5 μg/kg/h), MLK (morphine, 0.2 mg/kg/h; lidocaine, 3 mg/kg/h; and ketamine, 0.6 mg/kg/h), or DMLK (dexmedetomidine, 0.5 μg/kg/h; morphine, 0.2 mg/kg/h; lidocaine, 3 mg/kg/h; and ketamine 0.6 mg/kg/h). Among treatments, MAC of isoflurane was compared by means of a Friedman test with Conover posttest comparisons, and heart rate, direct arterial pressures, cardiac output, body temperature, inspired and expired gas concentrations, arterial blood gas values, and BIS were compared with repeated-measures ANOVA and a Dunn test for multiple comparisons.
Results:
Infusion of dexmedetomidine, MLK, and DMLK decreased the MAC of isoflurane from baseline by 30%, 55%, and 90%, respectively. Mean heart rates during dexmedetomidine and DMLK treatments was lower than that during MLK treatment. Compared with baseline values, mean heart rate decreased for all treatments, arterial pressure increased for the DMLK treatment, cardiac output decreased for the dexmedetomidine treatment, and BIS increased for the MLK and DMLK treatments. Time to extubation and sternal recumbency did not differ among treatments.
Conclusions and clinical relevance:
Infusion of dexmedetomidine, MLK, or DMLK reduced the MAC of isoflurane in dogs.
... To achieve a thorough examination in dogs, a deep plane of anesthesia is indicated (Noone 2001;Weil 2009) and high concentrations of volatile anesthetic agents may be required for maintenance of anesthesia. Modern inhalant anesthetics cause dose-dependent cardiovascular depression (Lowe et al. 1996), which can result in hypotension, a common complication during general anesthesia (Gaynor et al. 1999;Mazzaferro & Wagner 2001). Administration of opioids, sedatives, tranquilizers, and local anesthetics can be used as adjuncts to general anesthesia to reduce the amount of inhalant anesthetic required (Muir et al. 2003;Valverde et al. 2004). ...
To investigate the efficacy of maxillary and infraorbital nerve blocks for prevention of cardiovascular and qualitative responses to rhinoscopy, as well as response to skin clamping after assigned nerve block placement.
Randomized, blinded, placebo-controlled cross-over experimental study.
Eight random-source mixed breed dogs > 1 year old and weighing between 13 and 22 kg.
Within three anesthetic episodes, separated by at least 3 days, dogs were assigned to receive either 1 mL lidocaine 2% maxillary nerve block (ML); 0.5 mL lidocaine 2% infraorbital nerve block (IOL); or equal amounts of saline for maxillary or infraorbital nerve block combined as control treatment (S). Monitoring included temperature, respiratory rate, end-tidal CO2, ECG, heart rate (HR), systolic, diastolic and mean arterial pressure (SAP, DAP, MAP). Posterior (pR) and anterior rhinoscopies (aR) were performed and scored. Differences from baseline for outcome parameters HR, SAP, DAP, MAP were analyzed using repeated-measures anova, and results reported as mean ± SD. Binary scores for rhinoscopy were analyzed using logistic regression, and odds ratio was reported.
Changes from baseline for HR and SAP were significant for all treatments, besides ML for pR. Difference in changes from baseline among treatments was statistically significant for HR during pR with ML < S, and for SAP, DAP and MAP in right and left aR with ML < S and IOL > ML, except for DAP in left aR with only IOL > ML. Analysis of the binary score showed that the probability of a response for S and IOL treatments was nearly triple that of the ML treatment. None of the dogs, regardless of the treatments applied, responded to skin clamping.
Cardiovascular parameters do not seem to reflect the occurrence of adverse reactions during rhinoscopy. The maxillary nerve block is superior to the infraorbital nerve block, as applied in this study, in preventing adverse reactions during posterior rhinoscopy.
A female Swedish Elkhound was presented by the breeder at a referring clinic due to a swelling in the left mandibular area. The mass continued to grow, and at the age of 2 months the dog was referred to the hospital. Computed tomography was used for diagnostics of a unilateral external aneurysm of the left vena facialis and vena lingualis with a suspected centrally mineralised thrombus was made. One month later, the dog underwent surgery for removal of the aneurysm. This case describes the diagnostics, the perioperative anaesthetic considerations and anaesthetic management for surgery to remove the aneurysm where concerns regarding the young age and the risk of intraoperative haemorrhage were addressed. Premedication consisted of methadone and dexmedetomidine, general anaesthesia was induced using propofol and ketamine as co‐induction agents and maintained using isoflurane. There were no intraoperative anaesthetic complications; however, a postoperative surgical complication in the form of a seroma developed.
Objective
To investigate the frequency of perioperative acute kidney injury (AKI) in American Society of Anesthesiologists (SA) Grade I canine patients undergoing elective desexing using urine microscopy techniques and assess if pre‐ and intraoperative factors affect risk of developing AKI.
Design
Prospective observational clinical study conducted between September 2020 and October 2020.
Setting
University teaching hospital.
Animals
Thirty‐two female and four male dogs between 5 months and 5 years of age classified as ASA I undergoing elective desexing surgery.
Methods
Urinalysis was performed preoperatively and 20–24 h postoperatively to identify markers of renal tubular injury (RTI), particularly the presence of granular and renal tubular epithelial cell (RTEC) casts on sediment analysis. Dogs underwent a full physical examination and a preoperative assessment including measurement of urine specific gravity (USG), packed cell volume (PCV), total plasma protein and serum creatinine (sCr) was conducted as a part of the desexing programme. Anaesthetic records were examined for any evidence of intraoperative hypotension, defined as a mean arterial pressure (MAP) of <60 mmHg for any duration of time. MAP was measured using an indirect oscillometric technique. For analysis, animals were subdivided into affected and nonaffected groups, with affected animals those that had postoperative increases in granular and RTEC casts. Categorical and comparative analyses were then performed between groups to identify associations of increased casts with pre‐, intra‐ and postoperative variables.
Results
A frequency of RTI of 5.6% was identified. This was accompanied by a significant association between increases in casts with total duration ( p = 0.027) and number ( p = 0.016) of hypotensive episodes.
Conclusions
RTI is an anaesthetic consideration in ASA I veterinary patients undergoing elective desexing surgery. The identification of an association between the total duration and number of hypotensive episodes and the frequency of RTI highlights the importance of early detection of hypotension along with prompt and effective intervention in veterinary patients.
Objectives
To investigate the association between body mass and hypotension during general anaesthesia in dogs undergoing surgical and diagnostic procedures within a referral hospital.
Materials and Methods
Retrospective evaluation of the anaesthetic records of 1789 dogs was performed. Data on signalment, anaesthetic protocol and physiological variables, including mean arterial pressure, were collected. A multivariable generalised linear model was used to identify associations between explanatory variables, including body mass, and hypotension.
Results
In the population studied, increasing body mass (per 10 kg) was significantly associated with decreasing odds of hypotension (odds ratio 0.68; 95% confidence interval: 0.60 to 0.77). Additional variables associated with a decreased odds of hypotension were pre‐anaesthetic medication with alpha‐2 agonists (odds ratio 0.63; 95% confidence interval 0.48 to 0.82) and increased body temperature (per 1°C) during general anaesthesia (odds ratio 0.77; 95% confidence interval 0.67 to 0.88). Brachycephaly (odds ratio 1.72; 95% confidence interval 1.25 to 2.38), ASA physical status classification >3 (odds ratio 2.03; 95% confidence interval 1.16 to 3.56), undergoing a surgical procedure ( versus diagnostic) (odds ratio 1.57; 95% confidence interval 1.10 to 2.23) and bradycardia (odds ratio 1.37; 95% confidence interval 1.05 to 1.80) were independently associated with increased odds of hypotension.
Clinical significance
Dogs of lower body mass and brachycephalic breeds may be at higher risk of hypotension during general anaesthesia or alternatively represent subpopulations in which accurate blood pressure measurement presents a greater challenge. Monitoring blood pressure accurately in these groups requires particular attention and provisions for treating hypotension should be readily accessible.
This chapter addresses anesthetic considerations and protocols for patients with specific diseases. While some drugs may be ideal for a particular disease, the anesthetic protocol is often based on the anesthetist's familiarity, availability, and cost effectiveness of these drugs. Cardiovascular disease involves either a disturbance of the conduction system or an alteration of the structure of the heart itself. Structural abnormalities are broadly categorized into systolic, diastolic, and obstructive dysfunction. Diabetes insipidus is rare in veterinary patients. This disease occurs either centrally or at the level of the kidney; the patient either does not secrete or does not respond to antidiuretic hormone. Hepatic function is of critical importance to the anesthetist. It is responsible for protein synthesis, drug metabolism, glycogen storage, and production of coagulation factors. Renal disease is a broad term indicating dysfunction of the kidney. Upper airway disease involves the nasal passages, pharynx, and larynx.
Objectives
This study aimed to assess the effect of dexmedetomidine on the propofol-based anesthesia of cats subjected to ovariohysterectomy.
Methods
Twenty-eight cats were randomly allocated to four groups (seven cats in each) and premedicated with either 5 µg/kg dexmedetomidine (groups Dex 1, Dex 3 and Dex 5) or 0.05 ml saline (Prop group) intramuscularly. After the induction of anesthesia with propofol, total intravenous anesthesia was initiated with 300 µg/kg/min propofol plus 3 ml/kg/h NaCl 0.9% (Prop), or 200 µg/kg/min propofol plus dexmedetomidine at the rates of 1 µg/kg/h (Dex 1), 3 µg/kg/h (Dex 3) or 5 µg/kg/h (Dex 5). Cardiorespiratory variables were assessed 5 mins after induction and every 10 mins thereafter, until the end of anesthesia. The propofol infusion rate was adjusted every 10 mins (± 50 µg/kg/min) to maintain anesthetic depth. The times to extubation, sternal recumbency, ambulation and total recovery were recorded. Pain scoring was performed 1, 2, 4, 8, 12 and 24 h after the end of anesthesia.
Results
Dexmedetomidine produced a propofol-sparing effect of 72.8%, 71.1% and 74.6% in the Dex 1, Dex 3 and Dex 5 groups, respectively. Cats in the Prop group maintained higher heart rate values than the other groups, and the mean arterial pressure remained higher in the Dex 3 and Dex 5 groups. Rescue intraoperative analgesia (fentanyl bolus) was most frequent in the Prop group. There was no significant difference in the time of extubation. Cats in the Dex 1 and Dex 3 groups had a faster anesthetic recovery, with shorter times to achieving sternal recumbency, regaining ambulation and reaching full recovery. Cats in the Dex 1 and Dex 5 groups presented the best recovery quality scores, with 4 (range 4–5) and 4 (range 3–5), respectively, while the Prop group scored 1 (range 1–3), the worst anesthetic recovery score among the groups.
Conclusions and relevance
The use of dexmedetomidine as a total intravenous anesthesia adjuvant, especially at doses of 1 and 3 µg/kg/h, reduces propofol consumption and improves cardiorespiratory stability and intraoperative analgesia, while promoting a better and quicker recovery from anesthesia.
Introdução: Os felinos estão entre as principais espécies com os maiores índices de óbitos perianestésicos, apresentando as complicações transanestésicas como suas principais causas. Nesse sentido o conhecimento dessas complicações resulta em melhores intervenções corretivas e/ou profiláticas, favorecendo assim a redução destas complicações. Objetivo- O presente estudo teve como objetivo avaliar a incidência de complicações transanestésicas ocorridas em felinos submetidos a procedimentos cirúrgicos na Policlínica Veterinária Escola de Pequenos Animais da UNIFAA no período de 2018 a 2020. Material e métodos: Foram incluídos no estudo felinos que apresentavam fichas anestésicas que continham dados referentes a avaliação pré-anestésica, protocolo anestésico e monitoração transanestésica, devidamente preenchidos. Resultados: Foram analisados 241 registros anestésicos e 59 destes (24%) apresentaram dados transanestésicos satisfatórios para o desenvolvimento do estudo. Foram observadas complicações transanestésicas em 78% das fichas analisadas. As complicações mais incidentes foram: hipotensão arterial (29/ 64%) e bradipneia (27/ 60%). Os animais ASA I e ASA III apresentaram maior incidência de complicações cardiovasculares (60% e 100% respectivamente). Em contrapartida os animais ASA II apresentaram maior incidência de complicações respiratórias (80%). Além disso, os animais ASA I e ASA III apresentaram incidência de outras complicações (2% e 17% respectivamente). Não foram registrados óbitos perianestésicos no estudo. Conclusão: Através do presente estudo conclui-se que mesmo felinos saudáveis apresentam altas taxas de complicações. Dessa forma se faz necessário o monitoramento adequado de todos os pacientes independente de seu estado físico, bem como o preenchimento adequado dos dados anestésicos possibilitando assim melhorias na especialidade através de estudos retrospectivos.
Objective
To compare non-invasive (NIBP) with invasive blood pressure (IBP) measurements from a Datex S/5 Compact monitor in anaesthetized adult dogs, and to evaluate it according to the American College of Veterinary Internal Medicine (ACVIM) and the Association for the Advancement of Medical Instrumentation (AAMI) criteria.
Study design
Prospective clinical study.
Animals
A group of 34 client-owned adult dogs.
Materials and Methods
Dogs were anaesthetized for different surgical procedures using different anaesthetic protocols. IBP was measured using a catheter placed in a dorsal pedal artery. A blood pressure cuff was placed over the contralateral dorsal pedal artery for NIBP measurement. Data were recorded using the Datex iCollect program, and paired readings were matched every 3 minutes for 60 minutes. Bland-Altman and error grid analyses were used to estimate the agreement between IBP and NIBP measurements, and its clinical significance, respectively. Data were reported as mean bias [lower, upper limits of agreement (LoA)].
Results
The Datex S/5 monitor conformed with most ACVIM criteria. The correlation coefficient was less than 0.9 for systolic, diastolic, and mean arterial pressures. The best agreement between the non-invasive and invasive methods was observed for mean arterial pressure (MAP), with LoA (-17 to 13 mmHg) and higher percentage of the NIBP readings within 5 (55.6%), 10 (81.7%) and 20 (98.6%) mmHg of the IBP values. The Datex S/5 NIBP technology did not meet the AAMI validation criteria and less than 95% of the paired measurements were found within the green zone of the error grid analysis.
Conclusions and clinical relevance
The Datex S/5 monitor conformed with most ACVIM criteria but not with the more rigorous AAMI standards. Despite good agreement between IBP and NIBP for MAP measurements, care must be taken when using this device to guide therapeutic interventions on blood pressure in anaesthetized healthy adult dogs.
This article analyses the cardiovascular changes typically present in a patient with a gastric dilation volvulus. This pathogenesis results in the reduction of oxygen delivery to tissues through hypoperfusion, the translocation of GI bacteria and the release of proinflammatory cytokines. By highlighting these physiological changes, in an emergency case that can be seen at most practices, this article will aid more complete monitoring. This monitoring facilitates appropriate interventions and gives a more comprehensive outline of circulatory consequences.
This chapter provides an overview of cardiovascular physiology and pathophysiology, anesthetic agents, and cardiovascular patient evaluation, monitoring, and support during anesthesia to help the clinician prepare anesthetic plans for patients with mild to significant cardiovascular disease. Patients with cardiac disease should have some combination of preanesthetic electrocardiography, blood pressure (BP), thoracic radiographs, and echocardiogram depending on the type of cardiac disease. Systemic sedation that is appropriate for the patient's temperament and underlying disease in combination with locoregional analgesia may be sufficient for surgical analgesia in some cases. One major goal of adjunctive techniques or interventions is to increase cardiovascular stability and maximize CO and BP. Inotropes and vasopressors are drugs aimed at improving BP and perfusion by taking advantage of sympathetic nervous system receptor targets. The causes of heart failure or congestive heart failure are numerous and can be the result of a wide variety of cardiac diseases.
A three‐year‐old female neutered Staffordshire Bull Terrier underwent partial pancreatectomy for suspected insulinoma. During surgery, the patient developed severe hypotension unresponsive to reduction in inhalant agent concentration, intravenous fluid bolus therapy and intravenous administration of vasopressor agents. A progressive increase in arterial blood pressure values was only detected concomitantly with intravenous administration of methylene blue (MB), requested by the surgeon to facilitate the visualization of the pancreatic tumour. The arterial blood pressure remained within normal range values during the rest of the intraoperative period. The dog recovered uneventfully from general anaesthesia. To the author's knowledge, this is the first case report describing the effect of intravenous MB on arterial blood pressure in veterinary medicine.
Evidence‐based veterinary medicine (EBVM) is a set of tools for generating reliable research evidence, disseminating it to clinicians, and using it to support clinical decision making. EBVM provides a system for ensuring that the information clinicians need is not only accurate and relevant but available and easy to use. In the research environment, EBVM guides the design and conduct of scientific studies to minimize bias and ensure the data generated are reliable. EBVM includes techniques and training for clinicians to help identify their information needs and then find relevant and useful evidence. EBVM is useful in meeting our ethical obligations to pet owners. Pet owners have an ethical and often a legal right to be informed about the possible risks and benefits of medical interventions. EBVM methods should be a core part of veterinary medical training. EBVM helps veterinarians provide better care and client communication with greater confidence and less time and effort.
Veterinary medicine has made incredible strides regarding the sophistication of care that can be provided by veterinarians in practice. In practice, incremental care has been a part of veterinary medicine since its founding. The veterinary healthcare team are informed service providers. There are both ground‐up and top‐down approaches to implementing incremental care practices in the profession. Organized veterinary medicine also has a role to play. Incremental care is a philosophy that holds that there are medical options falling along the entire cost spectrum for most health conditions and that all the available options should be discussed with pet owners. This is in contrast to “gold standard care,” in which only the most effective and most expensive treatment options are, at least initially, presented. Licensing boards and legislatures are inconsistent in their approach to standards of care in veterinary medicine.
Prevalence and incidence are both terms used to describe the occurrence of a disease over a period of time. Epidemiology focuses on factors of disease, such as cause, risk factors, frequency, and distribution/pattern. Prevalence and incidence are terms commonly used when describing the study of epidemiology. Prevalence can be expressed over a period of time, referred to as period prevalence, and can also be expressed at a specific point in time, known as point prevalence. There are two ways in which incidence can be expressed: incidence risk and incidence rate. Prevalence is commonly utilized in veterinary medicine as it does not require defining the population that is at risk of developing that disease. Hemangiosarcoma is an aggressive form of cancer that is most commonly encountered in German shepherd dogs, Labrador retrievers, and golden retrievers. The incidence rate is the number of new cases per year divided by the at‐risk population per unit time.
Veterinary medical checklists are an effective strategy to reduce avoidable errors. Failures occur in every industry, including veterinary medicine. Comparisons are more difficult to make between veterinary medicine and the aviation industry due to the paucity of studies in the veterinary literature. There is one tool in particular that the aviation industry has relied upon that has gradually trickled into various facets of human healthcare: the checklist. In aviation, checklists may be used for ordinary procedures, such as take‐offs and landings, as well as for malfunctions and emergencies. Checklists in veterinary surgery are an appropriate tool to address surgical instrument retention, among other surgical errors. In addition to surgical errors, medical errors may occur in veterinary practice. Checklists are also important aspects of convergence schedules, to ensure that client communication is managed appropriately. Human‐based errors in medicine and surgery can and will happen to some degree to every veterinary practice and every healthcare provider.
Today's consumers want their healthcare on their own schedules, and at their own convenience. Veterinarians providing telehealth must comply with all laws and regulations associated with their license to practice veterinary medicine. Telehealth has the potential to enhance animal care and the delivery of veterinary services, and regulations are evolving accordingly. Veterinarians with a valid Veterinarian‐Client‐Patient Relationship (VCPR) have professional discretion to confer with specialists and consultants, but they remain the physicians of record and do not transfer that VCPR to the specialist or consultant. Veterinarians providing telehealth must be legally authorized to practice veterinary medicine. Technology is available that allows remote monitoring of pets, and this can be an important resource when considering virtual care. Remote monitoring can play a key role in wellness care. Veterinarians may initially have some worries that offering telehealth services will cannibalize their office visits, but such fears are generally unfounded.
Pet‐specific care is a concept that can revolutionize our approach to providing veterinary healthcare. When marketing veterinary services, it is important to know the client signalment as well as the patient signalment. The most effective way to market veterinary services is to customize the marketing strategy to target client demographics. Baby Boomers grew up during the American‐dream, white picket‐fence era post World War II. Steve Jobs and Bill Gates are both members of the Baby Boomer generation. Generation X is often referred to as the bridge between Millennials and Baby Boomers. Generation X also has strong brand loyalty, particularly to those brands who give back. Millennials began entering the workforce as the economy crashed, and as a result are the largest generation of entrepreneurs. The youngest generation that is beginning to develop its buying power is Generation Z, the iGeneration, or Gen Z.
Assessing risk accurately and using that assessment to inform medical care for patients is a skill that can be developed and improved. Wellness care is all about reducing risk. Some health risks are nearly universal, such as exposure to contagious diseases and parasites. In ill patients, risk analysis helps to guide us toward the most likely diagnoses so that we can diagnose and treat the pet appropriately. Risk assessment also guides our client education efforts. Some diseases are high risk for a great many dogs and cats. We should ensure that every client is aware of these common risks and has the opportunity to prevent or screen for these diseases when possible. The second way to prioritize risk is by seriousness of problem. A point scoring system may be useful for recommending wellness screening laboratory testing. Wellness plans can be designed to be the same for every patient or individualized for each patient.
With pet ownership comes risk that the pet may require substantial healthcare services and at considerable expense. Pet health insurance is one of the most common ways in which pet owners mitigate pet health risk. The ways in which individuals manage risk typically fall into one of four categories: avoidance, mitigation, transfer, and acceptance. Risk avoidance is the elimination of an exposure that has the potential to result in a negative outcome. Risk mitigation is an activity that may lessen the chance of a negative outcome associated with a particular risk. Most pet owners do not understand or plan for the true financial risk that comes along with being a pet owner. The best way to be fully prepared for the true financial risk of pet ownership is to transfer the risk to an insurance company by purchasing pet health insurance. Most people transfer risk through purchase of an insurance policy.
Owning a pet and providing appropriate veterinary care for that pet's lifetime costs more than most pet owners realize, and veterinarians need to be prepared to discuss costs at the time they make their recommendations. Transparent and upfront cost discussions with clients based on appropriate healthcare recommendations will lead to improved relationships, happier and more trusting clients, happier team members, and better outcomes for pets. Providing appropriate preventive and end‐of‐life care for a pet is only the tip of the iceberg when it comes to the total cost of pet ownership. If cost of care is a barrier, a veterinarian should offer payment assistance options rather than modifying the recommendations.
As more and more people embrace the perception of pets as family members, the veterinary profession has worked hard to meet the needs of a more demanding audience of veterinary caregivers. The escalating discrepancy between emotionally invested owners and the higher cost of advanced veterinary medicine has been widely characterized by industry analysts as an affordability crisis. The primary concern is that as the gap between veterinary cost and ability to pay widens, a lower percentage of pets will receive the treatments the industry has prepared for them. This chapter presents the primary affordability factors affecting the demand for veterinary services. It also presents supply‐side considerations factoring into the affordability of veterinary care. Pet owners are finding it difficult to pay for the more expensive veterinary services offered by an increasingly sophisticated veterinary profession, leading to what industry analysts have described as an affordability crisis.
Professional service providers have been particularly vexed after the provision of their service with both billing and collecting from their clients. There are whole consulting industries whose sole purpose is to provide professional service providers with the skills and support to actually charge a “full” price without providing discounts, and buoy the self‐worth of the provider. The goal of a sound patient payment discount program should be to: reward for expected good behavior on the part of compliance, reward the client for achieving strategic financial benchmarks, and reward intended patient intangibles such as marketing the practice to other potential clients. Some pet owners may prey on the humanistic trait of most veterinary hospitals to emphasize patient care over finances.
Blockchain may be a foreign concept to many, but it is an important topic because it is demonstrating real benefits in many aspects of human healthcare and is bound to gain more prominence in veterinary medicine as well. It could be particularly useful in pet‐specific care in which various stakeholders could have secure privileges to various aspects of the medical record. In a blockchain, individual records are bundled together into blocks, and then linked sequentially within the chain. The three parts of the process are thus: the record, the block, and the chain. To make sure only authorized users have access to the information, blockchain systems use cryptography‐based digital signatures to verify identities. Blockchain is more difficult to hack, and tends to be more secure than traditional systems.
The concept of placebo is well known in human medicine. In fact, the caregiver placebo effect may be evident around 30–40% of the time regarding subjective evaluations, such as for lameness in dogs and cats. Another manifestation of caregiver placebo effect can be seen as a feature of being enrolled in a study, or receiving an intervention perceived as new and potentially exciting – known as the Hawthorne effect. One very interesting aspect of placebo studies is that sometimes they can still provide benefits even if the patient/client knows they are administering placebos. This is known as the honest placebo effect. The nocebo effect is an interesting phenomenon in which people have negative expectations about something and that alone is enough to make them perceive an ill effect.
The human–animal bond (HAB) is the glue that keeps companion animals in families. Veterinary clinics and the wider community benefit from strong HABs. The HAB may affect owner decisions as to the choice of pet and where it is acquired, how the pet lives with them and owner lifestyle such as where they live, work, and take holidays. When veterinary clinic staff are aware of the HAB in general and, more specifically, the nature of their personal bond with their pets, it can help them support owners and accept different approaches to pet care. Compassion fatigue can occur when staff are interacting with clients whose attachment levels are very different from their own beliefs and attitudes about the HAB. Education of staff about the HAB and how it varies with different people can help staff accept owner decisions and minimize staff stress.
Veterinary professionals should play an active role in promoting the human–animal bond among their clients. Education should be taken beyond the typical exam room discussions to include alternative methods that are easily absorbed by pet owners. The human–animal bond is a mutually beneficial relationship between people and animals. In addition to traditional exam room conversations, some opportunities are considered to educate veterinarians' clients. These include: enhanced exam room communication, custom literature, practice blog and social media, educational open house, and community event. The entire veterinary healthcare team should contribute to educating clients on important topics that impact the human–animal bond. To promote the human–animal bond, veterinary professionals should educate clients on the importance of preventive care, fear, and stress in animals, positive reinforcement training, enrichment, exercise and nutrition, pain in pets, and pet health insurance.
The very good news is that pain management is now a central, and increasingly sophisticated, feature of small animal medicine and surgery, with an increasingly wide array of tools at the disposal of all members of the veterinary team. Underrecognized and undermanaged pain inflicts very real physiological and medical consequences, resulting in significant patient morbidity and in the extreme can contribute to mortality. Evidence‐based industry guidelines and consensus statements are available to direct veterinary clinicians to the highest, wisest, safest multimodal strategies for acute and chronic pain. Several clinical metrology instruments are validated for both dogs and cats to assign scores for acute postsurgical pain.
Disasters, man‐made or natural, can be devastating. Lives can be disrupted or lost, property damaged or destroyed. It is vitally important that veterinary practices have a written disaster plan to cover emergency relocation of animals, back‐up of medical records, continuity of operations, security, fire prevention, and insurance and legal issues. For practices affected by a disaster, first and foremost there needs to be an evacuation plan for people and animals. Veterinarians should be included in the larger local or state government's disaster planning, and veterinarian should have a role in the incident command system. Disaster planning needs to include preparation for continuity of operations. Sometimes clients will have to go to an emergency shelter that also allows pets. Having medical records, medications, food, and water ready to go will make the evacuation less stressful.
Sterilization surgery is considered the norm in North American dogs and cats, and is increasingly performed at young ages to prevent breeding of adopted dogs, and potentially reduce behaviors that may lead to relinquishment. The primary purpose of gonadectomy is to manage canine and feline populations. The majority of American veterinarians advocate for elective sterilization surgery. Most American dogs and cats undergo elective ovariohysterectomy (OVH) or castration within their first year of life. Neutering curbs unfavorable behaviors: castrated male dogs roam, mount, and urine‐mark less frequently, and male cats are less likely to spray. OVH is the standard sterilization surgery for bitches and queens in the US. Ovariectomy (OVE) may be performed as a minimally invasive technique using laparoscopy. The desire for less invasive procedures has led to the successful adoption of OVE in other countries. Pet overpopulation is a global, multifaceted, animal welfare issue.
The veterinary healthcare team (VHT) is on the front line of the intersection of animals and the people in their lives, and the One Health concept recognizes the interconnection between people, animals, and the environment they share. The VHT should be knowledgeable about how their actions fit into the larger picture of the human/animal environment. Zoonotic diseases are those that can pass between people and animals. Connection between human and animal health is the use and misuse of antibiotics. Antibiotic use should be restricted for appropriate bacterial diseases and education by the VHT will help clients understand this use. A distrust of commercial pet foods has led some clients to make their own pet food or sometimes veterinarians recommend homemade diets for pets with specific medical conditions. Clients with a love for exotic pets pose a unique challenge for VHTs. Wildlife poses a unique threat to pets and people.
Cancer is a disease of dysregulated genes. Personalized cancer medicine (Pmed) is a therapeutic approach to pet‐specific care that most often analyzes the molecular features of a patient's cancer, and uses this information to design treatment plans that target critical genetic alterations in that patient's tumor. Pmed can also be used to form the scientific rationale for new drug development that starts with the cancer patient rather than cancer cells in tissue culture. It is clear that cancer is a disease of dysregulated genomics. New genomic characterizations of cancer has fueled the field of precision medicine as a therapeutic approach, delivered recent drug approvals in human oncology, and is increasingly available to all species of cancer patients. Precision cancer medicine can be utilized to improve the understanding of a patient's cancer.
Patients with acute blindness typically present with mydriasis and a history of disorientation that may involve bumping into familiar objects. Acute blindness may be transient or permanent. For simplicity, lesions typically occur in one of three zones along this complex pathway: the retina, the optic nerve, or the visual cortex. Retinal lesions include dysplasia and degeneration syndromes, drug‐induced and taurine‐deficient retinopathies, and retinal detachment. Optic nerve lesions include optic neuritis and traumatic injury. Visual cortex lesions include hypotensive and ischemic encephalopathies and neoplasia. Disease localization is important for determining diagnosis and prognosis. Important disease localization and diagnostic tools involve the pupillary light reflex (PLR) and fundoscopy.
Objective:
To establish the incidence of intraoperative anaesthetic complications in dogs undergoing general anaesthesia (GA) for thoracolumbar hemilaminectomy (TH), to determine whether GA duration affects incidence of intraoperative complications and to identify associations between intraoperative complications.
Study design:
Retrospective observational study.
Animals:
A total of 224 client-owned dogs of various breeds undergoing TH for intervertebral disc extrusion.
Methods:
Anaesthetic records of dogs undergoing TH at a university teaching hospital between 2010 and 2016 were analysed. Data recorded included breed, sex, body weight, GA duration, magnetic resonance imaging (MRI) under the same GA, pharmacological intervention to increase heart rate (PIHR), hypotension (mean arterial blood pressure < 60 mmHg for ≥ 10 minutes), mechanical ventilation (MV) for inadequate ventilation, hypothermia (oesophageal temperature < 37 °C), oesophageal temperature ≥ 39 °C (T ≥ 39 °C), temperature trend, regurgitation and use of alpha-2 adrenoreceptor agonists, acepromazine, ketamine or lidocaine. Multivariate logistic regression models were fitted for hypothermia, T ≥ 39 °C, hypotension and PIHR with forced inclusion of GA duration.
Results:
Hypothermia was the most common complication (63.8% incidence), followed by MV implementation (63.4%), hypotension (33.9%), PIHR (24.6%), T ≥ 39 °C (20.5%) and regurgitation (4.9%). Multivariate models revealed that MRI and hypotension were associated with an increased risk of hypothermia, whilst increasing body weight, alpha-2 adrenoreceptor agonists and MV were associated with a reduced risk. Alpha-2 adrenoreceptor agonists and GA duration were associated with an increased risk of T ≥ 39 °C, whilst hypotension was associated with a reduced risk. Hypothermia and PIHR were associated with an increased risk of hypotension, whereas increased body weight was associated with a reduced risk. MV and hypothermia were associated with an increased risk of PIHR, whereas increased body weight was associated with a reduced risk.
Conclusions and clinical relevance:
Increasing GA duration was associated with increased risk of T ≥ 39 °C, but not any other intraoperative complications.
Background
A prospective, randomized, placebo-controlled, blinded clinical study was conducted to determine whether a single dose of midazolam affects the cardiovascular response to surgical manipulation of the ovaries during elective ovariohysterectomy. Thirty-nine client-owned dogs undergoing elective ovariohysterectomy were recruited. After scoring cage demeanour, dogs were premedicated with acepromazine (0.03 mg kg⁻¹) and pethidine (3 mg kg⁻¹) intramuscularly into the quadriceps muscle and 20 min later sedation was scored. Anaesthesia was induced with propofol intravenously (IV) to effect. The study treatment (group M: midazolam (0.25 mg kg⁻¹); or group P: placebo (Hartmann’s solution) (0.125 ml kg⁻¹)) was administered IV before the intra-operative manipulation of the first ovary. Anaesthesia was maintained with isoflurane in oxygen. Morphine (0.3 mg kg⁻¹ IV) was administered prior to the start of surgery. The vaporizer setting was adjusted according to the depth of anaesthesia. If an end-tidal isoflurane concentration (FE’Iso) above 1.6% was required additional analgesia was provided with fentanyl (2 μg kg⁻¹). Dogs received meloxicam (0.2 mg kg⁻¹ IV) at the end of procedure. Heart rate, mean arterial blood pressure, respiratory rate and end-tidal partial pressure of carbon dioxide as well as FE’Iso were recorded and analysed.
Results
A statistical significant difference between groups was detected in FE’Iso, with group M requiring a significantly lower FE’Iso than group P (14.3%) after administration of midazolam. No differences between groups was shown for percentage change in heart rate and mean arterial blood pressure, or end-tidal carbon dioxide and requirement for mechanical ventilation, or rescue analgesia. There was no statistically significant difference in the incidence of complications in group M and P. Group M received significantly more succinylated gelatin solution pre-administration of midazolam than group P, but no differences in fluid administration post-administration of the study treatment (midazolam/placebo) were detected. No statistical significant difference was demonstrated for the use of anticholinergic agents, dobutamine or noradrenaline.
Conclusion
No significant effect on cardiovascular parameters could be observed with administration of midazolam, but a modest (14.3%) isoflurane-sparing effect was detected.
This chapter discusses the equipment and techniques used to accurately monitor arterial and central venous blood pressure in veterinary patients. This includes normal values, anatomical sites, and equipment such as non‐invasive (oscillometric and Doppler) and invasive (intra‐arterial) techniques available for clinical use and research. In addition, techniques to quantify cardiac output are presented.
Although the utility and benefits of anesthesia and analgesia are irrefutable, their practice is not void of risks. Almost all drugs that produce anesthesia endanger cardiovascular stability by producing dose-dependent impairment of cardiac function, vascular reactivity, and compensatory autoregulatory responses. Whereas anesthesia-related depression of cardiac performance and arterial vasodilation are well recognized adverse effects contributing to anesthetic risk, far less emphasis has been placed on effects impacting venous physiology and venous return. The venous circulation, containing about 65–70% of the total blood volume, is a pivotal contributor to stroke volume and cardiac output. Vasodilation, particularly venodilation, is the primary cause of relative hypovolemia produced by anesthetic drugs and is often associated with increased venous compliance, decreased venous return, and reduced response to vasoactive substances. Depending on factors such as patient status and monitoring, a state of relative hypovolemia may remain clinically undetected, with impending consequences owing to impaired oxygen delivery and tissue perfusion. Concurrent processes related to comorbidities, hypothermia, inflammation, trauma, sepsis, or other causes of hemodynamic or metabolic compromise, may further exacerbate the condition. Despite scientific and technological advances, clinical monitoring and treatment of relative hypovolemia still pose relevant challenges to the anesthesiologist. This short perspective seeks to define relative hypovolemia, describe the venous system’s role in supporting normal cardiovascular function, characterize effects of anesthetic drugs on venous physiology, and address current considerations and challenges for monitoring and treatment of relative hypovolemia, with focus on insights for future therapies.
Measurement of arterial blood pressure (ABP) has a wide range of indications and is considered the “fourth vital sign” in critical care settings. It is responsible for tissue oxygenation, energy substrate delivery, and removal of metabolic byproducts. The pulsatile blood flow during ventricular contraction and relaxation results in two arterial blood pressure measurements: systolic and diastolic pressures. Direct ABP (dABP) monitoring is considered to be the “gold standard” for ABP measurement and indirect arterial blood pressure monitoring, also known as noninvasive blood pressure (NIBP) monitoring, is preferred when cardiovascular status is stable and large fluctuations in ABP are unlikely to occur. Many cardiac and vascular factors, as well as humoral and microcirculatory components, will affect the blood pressure. Low blood pressure (hypotension) is a frequent and often rectifiable cause of poor tissue perfusion in this setting. Tissues that are particularly sensitive to increased blood pressure (hypertension) include the ocular, cardiac, renal, and central nervous systems.
The peritoneum covers all walls of the abdominal cavity and all viscera within the abdominal cavity. Peritonitis, or inflammation of the peritoneum, may be classified as primary or secondary, localized or generalized, and aseptic or septic. Secondary generalized septic (bacterial) peritonitis is the most common form of peritonitis in small animals. Abdominal radiography and ultrasonography are useful diagnostic tools in cases of suspected peritonitis. Dogs and cats with septic peritonitis present with historical and physical examination findings similar to patients with acute abdominal disease of other causes. Many of the same challenges in the care of patients with septic peritonitis occur preoperatively and postoperatively, including hypotension, hypoalbuminemia, and altered coagulation. Surgery should be performed as soon as adequate efforts have been made to stabilize the patient's cardiovascular status and fluid balance. Principles of surgical therapy for septic peritonitis include source control, peritoneal lavage, and peritoneal drainage.
This study aimed to compare two methods of indirect measurement of blood pressure Doppler ultrasonic and oscillometric (PetMap), the direct method (arterial catheterization), relating them to the members and assessed which of these methods is most advisable for routine veterinary clinic. The left femoral artery was cannulated for measurement of mean arterial pressure by direct method. The right and left foreleg, right pelvic and tail were used to measure pressure by two indirect methods were evaluated for mean arterial pressure, systolic and diastolic.
Current literature suggests that severe anemia in dogs and cats increases plasma lactate (PL) levels. The aim of this prospective pilot study was to test the hypothesis that PL levels are increased in clinical patients (dogs and cats) presented with symptoms of anemia. Furthermore the correlations between PL, PCV and clinical symptoms were studied. 20 dogs and cats with a history of anemia (PCV < 0.2 l/l) were included. To exclude hypovolemia and dehydration as a potential reason for hyperlactatemia all patients were rehydrated intravenously with a nonlactate electrolyte solution Following rehydration pulse rate, respiration rate, body temperature, PCV, total solids and PL were recorded. 13 dogs aged from 3-14 years (M: 8 years), weight from 2.5-32 kg (M: 25 kg) and 7 cats aged from 1.513 years (M: 6 years), weight 3.4-7 kg (M: 5 kg) were included in the study. The duration of the clinical symptoms of anemia was 1-7 days (M: 4 days) in dogs and 1-35 days (M: 4 days) in cats. After rehydration laboratory parameters were: PCV 0.07-0.20 l/l (M: 0.16 l/l), TS 44-66 g/l (M: 56 g/l), PL 1.34.74 mmol/l (M: 2.83 mmol/l) in dogs and PCV0.08-0.18 l/l (M: 0.14 l/l), TS 46-84 g/l (M 6.4 g/l) and PL 1.28-6.42 mmoUl (M: 1.93 mmol/l) in cats. PL was elevated in 3 cats (43%) and 7 dogs (54 %). The correlation coefficient (r) of PL with heart rate and respiration rate was -0.006 and 0.102 in dogs and 0.376 and 0.663 in cats. PCV correlated with PL in dogs (r = -0.217) and in cats (r = 0.475). Thus, half of the dogs and cats had increased PL levels which did not correlate with PCV level. An increase in respiration rate is the most common clinical sign in animals with anemia and increased lactate. The resuits suggest an insufficient oxygen supply to the tissue, which should be remedied by oxygen application.
This chapter provides an overview of cardiovascular physiology and pathophysiology; anesthetic agents; and cardiovascular patient evaluation, monitoring, and support during anesthesia to help the clinician prepare anesthetic plans for patients with mild to significant cardiovascular disease. It explains the relationship between mean arterial pressure (MAP) and cardiac output (CO). When considering the relationship of measured blood pressure (BP) to the definition of oxygen delivery, one must understand the components that derive a measured BP. The presence of underlying cardiac disease necessitates a more extensive patient evaluation compared to noncardiac patients. Specific comments regarding positive inotropes and vasopressors are included in the chapter for each type of heart disease. The chapter lists the general strategies intended to be specific to a patient presenting with heart failure. It presents appropriate information for the clinician to prepare an individually tailored anesthesia plan for each patient presenting with cardiac disease.
The aim of this study was to report the anaesthetic management and peri-anaesthetic complications of 57 dogs undergoing pacemaker implantation at a referral institution over 10 years (2002-2012). The median duration of the procedure was 135 minutes (range 25-260 minutes). Patients were classified as American Society of Anaesthesiologist (ASA) III (42 cases) and ASA IV (15 cases). Forty-three patients had third-degree atrioventricular block, and 14 patients had sick sinus syndrome. The anaesthetic protocol most frequently chosen was pethidine (41 cases), etomidate-midazolam (43 cases) and isoflurane in oxygen for maintenance (57 cases). Transthoracic external pacing was used (43 cases) until the internal pacing lead was implanted. Atracurium was administered (48 cases) and intermittent positive pressure ventilation was applied in 52 cases. Complications observed included hypothermia (19 cases) and hypotension (5 cases). Three patients died (5.8%, 95% CI 1.1% to 14.6%) within the first 48 hours after termination of anaesthesia. The outcome for this procedure in sick animals appeared generally good though a number of complications were documented.
Osteosarcoma in dogs and humans share many similarities and the dog has been described as an excellent model to study this disease. The median survival in dogs has not improved in the last 25 years. Taurolidine has been shown to be cytotoxic to canine and human osteosarcoma in vitro. The goals of this study were to determine the pharmacokinetics and safety of taurolidine in healthy dogs and the safety of taurolidine in combination with doxorubicin or carboplatin in dogs with osteosarcoma.
Two percent taurolidine was infused into six healthy dogs (150 mg/kg) over a period of two hours and blood samples were taken periodically. One dog received taurolidine with polyvinylpyrrolidone (PVP) as its carrier and later received PVP-free taurolidine as did all other dogs in this study. Serum taurolidine concentrations were determined using high-performance liquid chromatography (HPLC) online coupled to ESI-MS/MS in the multiple reaction monitoring mode. Subsequently, the same dose of taurolidine was infused to seven dogs with osteosarcoma also treated with doxorubicin or carboplatin.
Taurolidine infusion was safe in 6 healthy dogs and there were no significant side effects. Maximum taurolidine serum concentrations ranged between 229 to 646 μM. The dog that received taurolidine with PVP had an immediate allergic reaction but recovered fully after the infusion was stopped. Three additional dogs with osteosarcoma received doxorubicin and taurolidine without PVP. Toxicities included dilated cardiomyopathy, protein-losing nephropathy, renal insufficiency and vasculopathy at the injection site. One dog was switched to carboplatin instead of doxorubicin and an additional 4 dogs with osteosarcoma received taurolidine-carboplatin combination. One incidence of ototoxicity occurred with the taurolidine- carboplatin combination. Bone marrow and gastro-intestinal toxicity did not appear increased with taurolidine over doxorubicin or carboplatin alone.
Taurolidine did not substantially exacerbate bone marrow or gastro-intestinal toxicity however, it is possible that taurolidine increased other toxicities of doxorubicin and carboplatin. Administering taurolidine in combination with 30 mg/m2 doxorubicin in dogs is not recommended but taurolidine in combination with carboplatin (300 mg/m2) appears safe.
To compare high definition oscillometry (HDO) to invasive blood pressure measurement in anaesthetized dogs.
Prospective, clinical trial.
Fifty dogs weighing 1.95–79 kg (mean 23.5 kg).
Anaesthetic and peri-anaesthetic management was chosen according to each dog's physical status and anaesthetist's preference. Direct arterial blood pressure measurements were performed using a catheter placed in the dorsal pedal artery and an electronic pressure transducer connected to a multiparameter monitor. Non-invasive blood pressure measurements were performed using an appropriately sized cuff placed around the tail base. Comparisons between the two methods were made using Bland and Altman plots. The data are reported as mean bias (lower, upper limits of agreement). Further analysis was performed after separating the data into the following categories based on invasive mean arterial blood pressure (MAP): high (MAP > 100 mmHg), medium (70 mmHg < MAP < 100 mmHg) and low (MAP < 70 mmHg) blood pressure (BP). The two methods were compared as used clinically.
Eight hundred measurement pairs for invasive and HDO BP readings were compared. Overall, the HDO measured lower values for SAP and DAP but higher for MAP than the invasive method. The lowest bias (upper, lower limits of agreement) were obtained for MAP, −1 (−22, 19) mmHg. The biggest discrepancy between the methods was reflected by a large bias (limits of agreement) 5 (−34, 45) mmHg, was for SAP. The results for DAP were between those for SAP and MAP with a bias (limits of agreement) of 3 (−20, 27) mmHg. When the values were separated into the pressure range categories the HDO measured higher in the high, medium and low BP groups, with the exception of SAP in the low BP group.
When considering the mean bias, the accuracy of HDO compared well with direct arterial blood pressure, but the precision was poor, as determined by wide limits of agreement.
Using trends and serial measurements rather than a single measurement for clinical decision making is recommended with both methods, when used as reported here.
Objective To evaluate quality of anaesthetic induction and cardiorespiratory effects following rapid intravenous (IV) injection of propofol or alfaxalone.
Study design Prospective, randomised, blinded clinical study.
Animals Sixty healthy dogs (ASA I/II) anaesthetized for elective surgery or diagnostic procedures.
Methods Premedication was intramuscular acepromazine (0.03 mg kg−1) and meperidine (pethidine) (3 mg kg−1). For anaesthetic induction dogs received either 3 mg kg−1 propofol (Group P) or 1.5 mg kg−1 alfaxalone (Group A) by rapid IV injection. Heart rate (HR), respiratory rate (fR) and oscillometric arterial pressures were recorded prior to induction, at endotracheal intubation and at 3 and 5 minutes post-intubation. The occurrence of post-induction apnoea or hypotension was recorded. Pre-induction sedation and aspects of induction quality were scored using 4 point scales. Data were analysed using Chi-squared tests, two sample t-tests and general linear model mixed effect anova (p < 0.05).
Results There were no significant differences between groups with respect to sex, age, body weight, fR, post-induction apnoea, arterial pressures, hypotension, SpO2, sedation score or quality of induction scores. Groups behaved differently over time with respect to HR. On induction HR decreased in Group P (−2 ± 28 beats minute−1) but increased in Group A (14 ± 33 beats minute−1) the difference being significant (p = 0.047). However HR change following premedication also differed between groups (p = 0.006). Arterial pressures decreased significantly over time in both groups and transient hypotension occurred in eight dogs (five in Group P, three in Group A). Post-induction apnoea occurred in 31 dogs (17 in Group P, 14 in Group A). Additional drug was required to achieve endotracheal intubation in two dogs.
Conclusions and Clinical relevance Rapid IV injection of propofol or alfaxalone provided suitable conditions for endotracheal intubation in healthy dogs but post-induction apnoea was observed commonly.
To assess the effects of dopamine and dobutamine on the blood pressure of isoflurane-anesthetized Hispaniolan Amazon parrots (Amazona ventralis).
8 Hispaniolan Amazon parrots.
A randomized crossover study was conducted. Each bird was anesthetized (anesthesia maintained by administration of 2.5% isoflurane in oxygen) and received 3 doses of each drug during a treatment period of 20 min/dose. Treatments were constant rate infusions (CRIs) of dobutamine (5, 10, and 15 μg/kg/min) and dopamine (5, 7, and 10 μg/kg/min). Direct systolic, diastolic, and mean arterial pressure measurements, heart rate, esophageal temperature, and end-tidal partial pressure of CO(2) were recorded throughout the treatment periods.
Mean ± SD of the systolic, mean, and diastolic arterial blood pressures at time 0 (initiation of a CRI) were 132.9 ± 22.1 mm Hg, 116.9 ± 20.5 mm Hg, and 101.9 ± 22.0 mm Hg, respectively. Dopamine resulted in significantly higher values than did dobutamine for the measured variables, except for end-tidal partial pressure of CO(2). Post hoc multiple comparisons revealed that the changes in arterial blood pressure were significantly different 4 to 7 minutes after initiation of a CRI. Overall, dopamine at rates of 7 and 10 μg/kg/min and dobutamine at a rate of 15 μg/kg/min caused the greatest increases in arterial blood pressure.
Dobutamine CRI at 5, 10, and 15 μg/kg/min and dopamine CRI at 5, 7, and 10 μg/kg/min may be useful in correcting severe hypotension in Hispaniolan Amazon parrots caused by anesthesia maintained with 2.5% isoflurane.
Objective – To determine the accuracy and precision of an oscillometric noninvasive blood pressure device as a predictor of invasive direct blood pressure in healthy anesthetized hypotensive and normotensive dogs.
Design – Prospective observational study.
Setting – University teaching hospital.
Animals – Eight crossbred adult dogs.
Interventions – Anesthesia was induced with propofol and maintained with isoflurane. A catheter was placed in the dorsal pedal artery to record systolic, mean, and diastolic arterial blood pressures (aSAP, aMAP, and aDAP, respectively). The noninvasive blood pressure device cuff was placed around the contralateral front limb to record noninvasive systolic, mean, and diastolic blood pressure (nSAP, nMAP, and nDAP). Two states of blood pressure (BP) were studied: baseline state was established by keeping end-tidal isoflurane concentration at 1.2±0.1%. The hypotensive state was achieved by maintaining the same isoflurane concentration while withdrawing approximately 40% of the animal's blood volume until aMAP was stable at approximately 40 mm Hg. At the end of the study, blood was returned to the animal and it was allowed to recover from anesthesia.
Measurements and Main Results – Agreement between the direct and indirect BP measurements was determined by the Bland-Altman method. The SAP and MAP but not DAP bias varied significantly between each BP state. Normotensive absolute biases (mean [SD]) for SAP, MAP, and DAP were −14.7 mm Hg (15.5 mm Hg), −16.4 mm Hg (12.1 mm Hg), and −14.1 mm Hg (15.8 mm Hg), respectively. Absolute biases during the hypotensive state for SAP, MAP, and DAP were −32 mm Hg (22.6 mm Hg), −24.2 mm Hg (19.5 mm Hg), and −16.8 mm Hg (17.2 mm Hg), respectively.
Conclusion – The oscillometric device was not reliably predictive of intra-arterial BP during hypotension associated with acute hemorrhage.
The medical records of 20 cats with post-anesthetic cortical blindness were reviewed. Information collected included signalment and health status, reason for anesthesia, anesthetic protocols and adverse events, post-anesthetic visual and neurological abnormalities, clinical outcome, and risk factors. The vascular anatomy of the cat brain was reviewed by cadaver dissections. Thirteen cats were anaesthetised for dentistry, four for endoscopy, two for neutering procedures and one for urethral obstruction. A mouth gag was used in 16/20 cats. Three cats had had cardiac arrest, whereas in the remaining 17 cases, no specific cause of blindness was identified. Seventeen cats (85%) had neurological deficits in addition to blindness. Fourteen of 20 cats (70%) had documented recovery of vision, whereas four (20%) remained blind. Two cats (10%) were lost to follow up while still blind. Ten of 17 cats (59%) with neurological deficits had full recovery from neurological disease, two (12%) had mild persistent deficits and one (6%) was euthanased as it failed to recover. Four cats (23%) without documented resolution of neurological signs were lost to follow up. Mouth gags were identified as a potential risk factor for cerebral ischemia and blindness in cats.
Two digital oscillometric human blood pressure measuring devices were modified and evaluated as blood pressure monitors in 12 healthy anesthetized dogs. Direct arterial pressures were measured via cannulation of the dorsal pedal artery and were correlated with indirect measurements through an inflatable cuff placed over the dorsal pedal artery below the hock joint of the contralateral limb. Direct and indirect measurements were compared for systolic, diastolic, and calculated mean arterial pressures. Blood pressure ranges between 215/145 mm of Hg and 65/30 mm of Hg were obtained, using combinations of halothane, phenylephrine, calcium, and IV administered fluids. Machine A was found to be insufficient for clinical application, on the basis of correlation coefficients between direct and indirect pressures of 0.78, 0.65, and 0.74 for systolic, diastolic, and mean arterial pressures, respectively. Higher correlation coefficients between direct and indirect pressures (0.77, 0.87, and 0.87, respectively) were obtained with machine B. The results of the study reported here suggest machine B may be an effective blood pressure monitoring device in anesthetized dogs.
The cardiopulmonary effects of a halothane/oxygen combination were studied in eight cats subjected to a 25% whole blood volume loss. Test parameters included cardiac output measured via thermodilution, heart rate, respiratory rate, arterial blood pressure (systolic, diastolic and mean) and blood gas analysis. Values for cardiac index, stroke volume and systemic vascular resistance were calculated from these data. Posthemorrhage cardiac output, cardiac index, stroke volume and measurements of arterial blood pressure were significantly decreased (p less than 0.05). Heart rate remained unchanged. Following induction of halothane anesthesia the above parameters experienced a further significant decline (p less than 0.05) from their immediate preanesthetic (i.e. posthemorrhage) values. Heart rate also significantly decreased (p less than 0.05). Thirty minutes following the cessation of halothane anesthesia these values returned to near-hemorrhage levels, being above their respective preanesthetic values. Systemic vascular resistance initially rose, peaking ten minutes into halothane anesthesia, before gradually falling to prehemorrhage values at the end of halothane anesthesia. Following hemorrhage, respiratory rate demonstrated a transient increase, associated with an arterial CO2 tension fall, before returning to initial values at the preanesthetic time. During halothane anesthesia respiratory rate remained unchanged whereas arterial CO2 tension rose significantly (p less than 0.05) and pH declined slightly from preanesthetic readings. These returned to prehemorrhage values 30 minutes following the cessation of halothane anesthesia.
The cardiopulmonary effects of a ketamine/ acepromazine combination was studied in ten cats subjected to a 25% whole blood volume loss. Test parameters included cardiac output, measured via thermodilution, heart rate, respiratory rate, arterial blood pressure (systolic, diastolic and mean) and blood gas analysis. Values for cardiac index, stroke volume and systemic vascular resistance were calculated from these data. Posthemorrhage, cardiac output, cardiac index, stroke volume, heart rate and measurements of arterial blood pressure were significantly decreased (p less than 0.05). Following the induction of ketamine/ acepromazine anesthesia, cardiac output, cardiac index, stroke volume and heart rate showed mild but statistically insignificant declines and were above their respective posthemorrhage values 120 min into ketamine/ acepromazine anesthesia. Measurements of arterial blood pressure showed further declines from their respective posthemorrhage values that were statistically significant (p less than 0.05). Following hemorrhage, respiratory rate increased significantly (p less than 0.05), associated with a fall in arterial CO2 tension. During ketamine/ acepromazine anesthesia, respiratory rate showed a dramatic and significant decline (p less than 0.05) with arterial CO2 tension rising to prehemorrhage values. Systemic vascular resistance, arterial O2 tension and pH remained essentially unchanged throughout the experimental period.
Cardiopulmonary function was assessed in healthy cats premedicated with intramuscular acepromazine, meperidine, atropine combination (premix), followed by induction and maintenance with intravenous thiopental for 30 min. Cardiac output by thermodilution, heart rate, blood pressure and blood gas analysis were evaluated over 120 min. A minor degree of respiratory depression was noted in the cats. Cardiac index (cardiac output/kg) was significantly depressed following thiopental induction and for the entire 120 min studied. Stroke volume was significantly reduced after premix administration and for 90 min posthiopental induction. No significant change in heart rate, systemic vascular resistance or blood pressure was observed. Significant cardiovascular depression was produced by the premedicant, and this persisted following thiopental anesthesia.
The effects of dobutamine ([+/-]-4-[2-[[3-(p-hydroxyphenyl)-1-methyl propyl] amino] ethyl] pyrocatechol hydrochloride), a new synthetic cardioactive sympathomimetic amine, were examined on direct and continuous measurements of left ventricular (LV) diameter (D), pressures (P), velocity of shortening (V), dP/dt, dP/dt/P, arterial pressure, cardiac output, and regional blood flows in the left circumflex coronary, mesenteric, renal, and iliac beds in healthy, conscious dogs. At the highest dose of dobutamine examined, 40 mug/kg/min, the drug increased dP/dt/P from 65+/-3 to 128+/-4 s(-1) and isolength velocity from 72+/-4 to 120+/-7 mm/s without affecting LV end diastolic D significantly. Mean arterial P rose from 92+/-2 to 104+/-3 mm Hg and heart rate from 78+/-3 to 111+/-7 beats/min, while LV end systolic D fell from 24.1+/-1.4 to 19.9+/-1.8 mm, reflecting a rise in stroke volume from 30+/-4 to 42+/-3 ml. Cardiac output rose from 2.41+/-0.23 to 4.35+/-0.28 liter/min, while calculated total peripheral resistance declined from 0.042+/-0.005 to 0.028+/-0.003 mm Hg/ml/min. The greatest increases in flow and decreases in calculated resistance occurred in the iliac and coronary beds, and the least occurred in the renal bed. Propranolol blocked the inotropic and beta(2) dilator responses while vasoconstricting effects mediated by alpha adrenergic stimulation remained in each of the beds studied. When dobutamine was infused after a combination of practolol and phentolamine, dilatation occurred in each of the beds studied. These observations indicate that dobutamine is a potent positive inotropic agent with relatively slight effects on preload, afterload, or heart rate, and thus may be a potentially useful clinical agent. The one property of this drug which is not ideal is its tendency to cause a redistribution of cardiac output favoring the muscular beds at the expense of the kidney and visceral beds.
An important consideration in the evaluation of pharmacologic agents used in low-cardiac-output states is the relative effect of these agents on myocardial oxidative demands. To date, it is not known whether any of the catecholamines possess a relative advantage or disadvantage due to differences in myocardial oxygen consumption (ṀVo2) in the ejecting heart, independent of differences in the hemodynamic correlates of ṀVo2 In this study, the ṀVo2 effects of epinephrine, isoproterenol, dopamine, norepinephrine, and dobutamine were examined at both high- and low-dosage levels under conditions of controlled hemodynamics; the studies were performed in nonfailing canine hearts with low initial left ventricular end-diastolic pressures. In high doses, dobutamine was found to increase ṀVo2 significantly more than epinephrine and isoproterenol, and epinephrine increased ṀVo2 more than isoproternol, but these observations could be explained by the effects of dobutamine and epinephrine on the hemodynamic corelates of ṀVo2. Otherwise, for comparable changes in the hemodynamic correlates of ṀVo2, the changes in ṀVo2 were similar irrespective of the catecholamine under study. These ata lend support to the thesis that cardiac-active catecholamines administered for inotropic support cause similar increases in the consumption of oxygen by the myocardium; thus, selection of a given catecholamine for inotropic support should include other criteria than just the direct effect of the agent on myocardial oxidative metabolism.
Objective —To determine the accuracy of three indirect blood pressure monitoring techniques (oscillometric technique [OS], Doppler [DOP], and optical plethysmography [OP] [blood pressure determined with a pulse oximeter waveform]) when compared with direct arterial pressure measurement in cats.
Study Design —Prospective study.
Animal Population —Eight healthy (five female, three male), domestic short‐hair cats, weighing 3.5 ± 0.8 kg
Methods —Cats were anesthetized with isoflurane. The inspired concentration of isoflurane was adjusted to produce mild hypotension (80 to 100 mm Hg direct systolic), moderate hypotension (60 to 80 mm Hg direct systolic), and severe hypotension (<60 mm Hg direct systolic). Indirect pressure measurements were obtained from the thoracic limb and compared with concurrent direct measurement using regression analysis and a modification of Bland and Altman's technique.
Results —All three techniques underestimated systolic pressure. OS produced the best prediction of systolic pressure with a bias ± precision of ‐15.9 ± 8.1 mm Hg. DOP and OP were relatively inaccurate with a bias ± precision of ‐25 ± 7.4 mm Hg and ‐25 ± 7.5 mm Hg. All three techniques correlated well with direct pressure with r values of 0.81, 0.88, and 0.88 for OS, DOP, and OP. DOP and OP provided an accurate prediction of direct mean arterial pressure with a bias ± precision of ‐0.8 ± 6 mm Hg and 0.6 ± 5.5 mm Hg. Correlation was good between DOP and mean arterial pressure with r = 0.89. Correlation was also good between OP and mean arterial pressure with r = 0.90.
Conclusions —OS provided the most accurate prediction of direct systolic pressure. DOP and OP provided a good prediction of mean arterial pressure in the cat.
Clinical Relevance —All three of these techniques are useful for detecting trends. Direct monitoring of blood pressure should be considered if accurate blood pressure measurement is required.
The data from this study document that dobutamine is a powerful inotropic agent in anesthetized dogs with acute myocardial ischemia and in awake, unsedated ones with chronic myocardial infarction. Dobutamine significantly increases heart rate at relatively small doses in anesthetized dogs with acute myocardial ischemia but considerably larger amounts of dobutamine are required to significantly increase heart rate in awake, unsedated dogs with myocardial infarction. Dobutamine also significantly increases regional myocardial blood flow to all areas of the heart at 20mug/kg/min in both anesthetized dogs with acute myocardial ischemia and awake, unsedated ones with myocardial infarction. However, in anesthetized dogs 20mug/kg/min of dobutamine significantly increases epicardial ST-segment elevation during acute myocardial ischemia. Propranolol prevents the inotropic and chronotropic effects of dobutamine in both anesthetized and awake, unsedated dogs. This study suggests that during experimental acute myocardial ischemia dobutamine given at doses that significantly increase heart rate and contractility may increase the extent of myocardial damage. The data also suggest that this agent should be of value in the setting of severe myocardial depression without associated severe coronary artery disease to increase cardiac contractility at doses that do not markedly alter heart rate. The hemodynamic and coronary blood flow effects of dobutamine in patients with and without severe coronary artery disease should be evaluated.
The systemic and coronary hemodynamic effects of desflurane were compared to those of isoflurane, halothane, and enflurane in chronically instrumented dogs. Since autonomic nervous system function may significantly influence the hemodynamic actions of anesthetics in vivo, a series of experiments also was performed in the presence of pharmacologic blockade of the autonomic nervous system. Eight groups comprising a total of 80 experiments were performed on 10 dogs instrumented for measurement of aortic and left ventricular pressure, the peak rate of increase of left ventricular pressure (dP/dt), subendocardial segment length, coronary blood flow velocity, and cardiac output. Systemic and coronary hemodynamics were recorded in the conscious state and after 30 min equilibration at 1.25 and 1.75 MAC desflurane, isoflurane, halothane, and enflurane. Desflurane (+79 +/- 12% change from control) produced greater increases in heart rate than did halothane (+44 +/- 12% change from control) or enflurane (+44 +/- 9% change from control) at 1.75 MAC. Desflurane preserved mean arterial pressure to a greater degree than did equianesthetic concentrations of isoflurane. This result was attributed to a smaller effect on peripheral vascular resistance as compared to isoflurane and greater preservation of myocardial contractility as evaluated by peak positive left ventricular dP/dt and the rate of increase of ventricular pressure at 50 mmHg (dP/dt50) compared to other volatile anesthetics. Increases in diastolic coronary blood flow velocity (+19 +/- 6 and +35 +/- 12% change from control at 1.75 MAC, respectively) and concomitant decreases in diastolic coronary vascular resistance (-41 +/- 12 and -58 +/- 6% change from control at 1.75 MAC, respectively) were produced by desflurane and isoflurane. In the presence of autonomic nervous system blockade, the actions of desflurane and isoflurane were nearly identical with the exception of coronary vasodilation. After autonomic nervous system blockade, isoflurane increased coronary blood flow velocity, but desflurane did not. Furthermore, both desflurane and isoflurane continued to produce less depression of myocardial contractility than did halothane and enflurane. In summary, at equianesthetic concentrations, desflurane and isoflurane produced similar hemodynamic effects; however, in the absence of drugs that inhibit autonomic reflexes, desflurane had less negative inotropic activity and produced less decrease in arterial pressure. The coronary vasodilator actions of desflurane and isoflurane within the limitations of this model were not similar. When the increase in heart rate and rate-pressure product produced by desflurane were prevented in dogs with autonomic nervous system blockade, desflurane produced no change in coronary blood flow velocity.
Cardiovascular, pulmonary, and behavioral effects of multiple doses of oxymorphone in 10 nonanesthetized, spontaneously breathing, healthy dogs were studied, Oxymorphone (0.4 mg/kg of body weight) was administered iv , and at 20, 40, and 60 minutes after the first injection was given, 0.2 mg of oxymorphone/kg was administered. Cardiovascular and pulmonary variables were measured before (base line) and at 5, 15, 35, 55, 75, 100, 120, 150, 180, 210, 240, 270, and 300 minutes after the first oxymorphone injection. Degree of sedation and behavioral effects also were recorded. Naloxone (0.04 mg/kg, iv ) was administered 4.5 hours after the 4th oxymorphone injection, and behavioral changes were recorded.
Oxymorphone induced mild respiratory depression. After transient apnea developed, respiratory rate increased to a pant, tidal volume decreased, and minute ventilation increased, but these values were not significantly ( P =0.05) different from base line. The Pa CO 2 , physiologic dead space, and base deficit increased; alveolar tidal volume decreased; and alveolar minute ventilation did not change. The Pa O 2 decreased, hemoglobin and arterial O 2 content increased, and O 2 transport did not change. Venous admixture transiently increased.
Oxymorphone induced minimal cardiovascular depression. Mean arterial blood pressure, stroke volume, central venous pressure, pulmonary artery pressure, and pulmonary wedge pressure increased. Heart rate decreased, systemic vascular resistance transiently increased, and cardiac output transiently decreased. Because the dogs moved spontaneously, responded to sound with sudden, vigorous movements, and breathed with excessive effort, oxymorphone alone was considered inadequate as a general anesthetic.
Exogenously administered vasopressors (sympathomimetics) were evaluated in halothane-anesthetized dogs to determine the effects of these drugs on cardiovascular function before and after hemorrhage.
Six dogs were anesthetized with thiamylal sodium (20 mg/kg of body weight) and halothane (1.25 minimal alveolar concentration) in 100% oxygen. After instrumentation, cardiac output, systemic arterial blood pressure ( sap ), heart rate ( hr ), left ventricular pressure, pulmonary arterial pressure, and an index of cardiac contractility (dP/dT) were measured. Stroke volume, cardiac index ( ci ), stroke index ( si ), rate-pressure product, and systemic vascular resistance ( svr ) were calculated. Epinephrine (0.1, 0.3. and 0,5 μg/kg/min (low, medium, and high doses respectively]) and dobutamine (1, 5, and 10 μg/kg/min [low, medium, and high doses, respectively]) were infused. Methoxamine was given in a bolus of 0.22 mg/kg, iv . All measurements were taken at 2.5 minutes after infusion, and were repeated after removal of 40% of the estimated blood volume.
Dobutamine administered at the low dose before hemorrhage increased sap and dP/dT. At the high and medium dose, dobutamine significantly increased ci , si dP/dT, and sap , with no significant change in hr or svr . The nedium dose of epinephrine was the most effective dose of epinephrine at increasing key variables ( ci , si , dP/dT). The response of ci and si to this dose was not significantly different from the changes seen with high-dose administration of dobutamine. The dP/dT was significantly lower with epinephrine than with dobutamine, and svr and hr were unchanged with epinephrine, except at the low dose, which decreased svr . Methoxamine significantly deceased ci , si and hr , whereas svr and sap were increased significantly.
After hemorrhage, the only variables that had a signficant change in the absolute magnitude of the response, to a drug, relative to the response before hemorrhage, were a significantly reduced ability of dobutamine and nethoxamine to increase sap , and a significantly debased ability of methoxamine to decrease ci .
We concluded that dobutamine and epinephrine provide beneficial short-term support of the cardiovascular system in the halothane-anesthetized dog during acute hypovolemia.
The effects of iv dobutamine and dopamine infusions were studied at six incremental doses (range 5 to 160 micrograms/kg.min) in two groups of five dogs. Dobutamine decreased the systemic vascular resistance (SVR), without significant changes in mean arterial pressure (MAP), or pulmonary vascular resistance (PVR). Dopamine increased MAP, SVR, and PVR, except for a decrease at 10 micrograms/kg.min. Both drugs produced dose-related increases in cardiac output and venous admixture; however, with dopamine the dose-response curve reached a plateau at doses greater than 40 micrograms/kg.min. While the oxygen consumption (VO2) increased progressively in both groups, the oxygen availability ratio (DO2/VO2) and arteriovenous oxygen content difference (CaO2 - CvO2) were maintained mainly by increased cardiac output in the dobutamine group and hemoglobin concentration in the dopamine group. Thirty minutes after termination of drug infusions, the DO2/VO2 dropped, and CaO2 - CvO2 increased significantly in both groups. These changes were mainly due to sustained high VO2; however, in the dopamine group, a larger imbalance resulted from further decreases in cardiac output to levels below the control value.
The arrhythmogenicity of epinephrine, dopamine, and dobutamine, administered by constant-rate infusion, was determined in vagotomized and nonvagotomized thiamylal-halothane anesthetized dogs. Electrocardiograms and atrioventricular bundle electrograms revealed the development of atrial, junctional, and ventricular arrhythmias. The 3 drugs produced atrial arrhythmias at dosages smaller than those required to produce ventricular arrhythmias. The mean dosages (microgram/kg-1/min-1) required to produce ventricular arrhythmias on duplicate trials in vagotomized dogs were for epinephrine, 0.6 +/- 0.2; dopamine, 22.8 +/- 14.8; and dobutamine, 11.6 +/- 5.2. The corresponding doses for nonvagotomized dogs were for epinephrine, 0.8 +/- 0.3; dopamine, 35.3 +/- 13.5; and dobutamine, 21.9 +/- 13.9. Most ventricular arrhythmias originated from a single focus in the left ventricle. Heart rate and blood pressure were significantly increased immediately before ventricular arrhythmia appeared. We conclude that epinephrine, dopamine, and dobutamine are capable of producing cardiac arrhythmias in vagotomized and nonvagotomized thiamylal-halothane anesthetized dogs and that bilateral vagotomy decreases the dosage of epinephrine, dopamine, and dobutamine required to produce cardiac arrhythmias.
Cardiovascular effects of iv administered ketamine (10 mg/kg) and midazolam (0.5 mg/kg) were determined in 12 healthy isoflurane-anesthetized (1.7% end-tidal concentration) dogs. Six dogs received a ketamine-midazolam combination ( k-m ) as a bolus over 30 seconds and 6 dogs received k-m as an infusion over 15 minutes. Ketamine-midazolam combination as a bolus and an infusion caused early significant ( P < 0.05) reductions in mean systemic blood pressure, cardiac index, and stroke index, which returned to baseline values near the end of the study. Heart rate decreased significantly ( P < 0.05) in dogs of the infusion group and returned to the baseline value near the end of the study. One dog died after k-m bolus administration. Mean maximal decreases from baseline for systemic blood pressure, cardiac index, and stroke index were significantly ( P < 0.05) greater in dogs of the bolus group than in dogs of the infusion group; therefore, cardiovascular effects of k-m after infusion were less severe than those after bolus. Base excess and pHa decreased significantly ( P < 0.05) in the infusion group, although similar changes occurred in both groups.
Four dogs were maintained with 1.7% end-tidal isoflurane to determine temporal effects of isoflurane; these dogs did not receive k-m . Increases in heart rate, cardiac index, stroke index, and left and right ventricular stroke work indexes were significant ( P < 0.05) at various sample collection intervals, particularly during the later stages of the study.
Isoflurane anesthesia effectively blocked the cardiostimulatory properties of k-m . Ketamine-midazolam combination should be used cautiously during isoflurane anesthesia, and administration by slow infusion may be safer than by rapid bolus administration.
Twelve healthy dogs were used to determine the cardiorespiratory effects of i.v. administered ketamine (10 mg/kg of body weight) and midazolam (0.5 mg/kg). Half the dogs received a ketamine-midazolam combination (K-M) as a bolus over 30 seconds and the other half received the K-M as an infusion over 15 minutes. Induction of anesthesia by use of K-M was good in all dogs. Ketamine-midazolam combination as a bolus or infusion induced minimal cardiorespiratory effects, except for significant (P < 0.05) increases in mean heart rate and rate-pressure product. The increase in heart rate was greater in dogs of the infusion group. Mild and transient respiratory depression was observed in dogs of both groups immediately after administration of K-M, but was greater in dogs of the bolus group than in dogs of the infusion group. Duration of action of K-M for chemical restraint was short. Salivation and defecation were observed in a few dogs. Extreme muscular tone developed in 1 dog after K-M bolus administration.
The hemodynamic effects of 2 dosages of ephedrine were studied in 6 dogs anesthetized with isoflurane only (end-tidal concentration equivalent to 1.5 times minimum alveolar concentration). Following instrumentation, baseline (time 0) measurements included heart rate (HR), respiratory rate, mean arterial blood pressure (MAP), cardiac output, and blood gas tensions. Cardiac index (CI), stroke volume (SV), systemic vascular resistance (SVR), arterial oxygen content (CaO2), and oxygen delivery and consumption (DO2 and VO2, respectively) were calculated. Three dogs were given ephedrine IV at a dosage of 0.1 mg/kg of body weight, and 3 dogs were given ephedrine IV at a dosage of 0.25 mg/kg. Measurements were recorded at 5, 10, 15, 30, and 60 minutes. Each dog then received the alternate dosage of ephedrine, and measurements were again recorded at the same intervals. Effects of ephedrine varied with dosage. Neither dosage was associated with significant changes in pH, PaO2, PaCO2, VO2, or respiratory rate. Ephedrine at a dosage of 0.1 mg/kg caused transient significant increases in MAP, CI, SV, CaO2, and DO2, significant decreases in HR and SVR, and a late, slight decrease in CaO2. Ephedrine at a dosage of 0.25 mg/kg caused a greater and more prolonged increase in MAP, as well as increases in CI, SV, and SVR, and a decrease in HR. The higher dosage of ephedrine also caused a pronounced increase in hemoglobin concentration and CaO2, resulting in a 20 to 35% increase in DO2 throughout the 60-minute experiment.
To characterize the hemodynamic effects of medetomidine administered intravenously at doses ranging from 1 to 20 microg/kg, and to determine whether these effects are dose dependent.
Prospective randomized multidose trial.
Twenty-five clinically normal male beagles (5 groups of 5), aged 1 to 4 years and weighing 13.5 +/- 1.7 kg.
Medetomidine, at a dose of 1, 2, 5, 10, or 20 microg/kg, was administered intravenously at time 0. Heart rate, arterial pressure, central venous pressure, mean pulmonary arterial pressure, pulmonary capillary wedge pressure, body temperature, cardiac output, and packed cell volume were measured immediately before and at selected times after medetomidine administration (3, 7, 10, 20, 30, 40, 50, and 60 minutes in all groups, at 90 minutes for the 10 and 20 microg/kg groups, and at 120 minutes for the highest dose). Cardiac index, stroke index, rate-pressure product, systemic vascular resistance index, pulmonary vascular resistance index, and left and right ventricular stroke work indices were calculated. The degree of sedation was subjectively scored by an observer who was blinded to the treatment used.
Heart rate, rate-pressure product, cardiac index, and left and right ventricular stroke work indices decreased below baseline values. Central venous pressure and systemic vascular resistance index increased above baseline measurements. Except in the 2 microg/kg group, after an initial and short lasting increase, a prolonged decrease in arterial pressure was observed.
Hemodynamic changes were observed with the intravenous (IV) administration of medetomidine, at any dose. However, the two lowest doses (1 and 2 microg/kg) produced less cardiovascular depression.
Medetomidine is an alpha-2 adrenoceptor agonist widely used in dogs, producing sedation, analgesia and cardiovascular depression. When using IV medetomidine, a reduction of the recommended dosage (ie, +/-30 to 40 microg/kg) by up to 6 times did not significantly influence the cardiovascular effects.
Veterinary care has continued to advance by implementing more of the equipment and techniques that are commonly used in human medicine. This includes the placement of arterial catheters and pulmonary artery catheters and continuous monitoring of arterial pressure, central venous pressure, and pulmonary artery pressure. This article describes the technique for placement of appropriate catheters, the equipment that is needed, and the waveforms that are obtained when measuring direct arterial pressures, central venous pressures, and pulmonary arterial pressures.