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Sonographic evaluation of epidural and intrathecal injections in cats
Abstract
Objectives:
To describe the ultrasonographic anatomy of the caudal lumbar spine in cats and to detect ultrasound (US) signs associated with epidural or intrathecal injection.
Study design:
Prospective, clinical study.
Animals:
Twenty-six client-owned cats.
Methods:
Transverse (position 1) and parasagittal (position 2) two-dimensional US scanning was performed over the caudal lumbar spine in all cats. Midline distances between the identified structures were measured. Cats assigned to epidural injection (group E, n = 16) were administered a bupivacaine-morphine combination confirmed by electrical stimulation. Cats assigned to intrathecal injection (group I, n = 10) were administered a morphine-iohexol combination injected at the lumbosacral level and confirmed by lateral radiography. The total volume injected (0.3 mL kg(-1) ) was divided into two equal aliquots that were injected without needle repositioning, with the US probe in positions 1 and 2, respectively. The presence or absence of a burst of color [color flow Doppler test (CFDT)], dural sac collapse and epidural space enlargement were registered during and after both injections.
Results:
US scanning allowed measurement of the distances between the highly visible structures inside the spinal canal. CFDT was positive for all animals in group E. In group I, intrathecal injection was confirmed in only two animals, for which the CFDT was negative; seven cats inadvertently and simultaneously were administered an epidural injection and showed a positive CFDT during the second aliquot injection, and the remaining animal was administered epidural anesthesia and was excluded from the CFDT data analysis. Dural sac collapse and epidural space enlargement were present in all animals in which an epidural injection was confirmed.
Conclusions and clinical relevance:
US examination allowed an anatomical description of the caudal lumbar spine and real-time confirmation of epidural injection by observation of a positive CFDT, dural sac collapse and epidural space enlargement.
... The ultrasound visualisation of the structures was very similar to the one observed in cats. 32 In cats, the use of 22-G spinal needles to perform epidural injections may lead to an unsuccessful epidural block, dural laceration or inadvertent intrathecal injection as the eye of the spinal needle is wider than the dorsal epidural space. 32 Since the dorsal epidural space in rabbits may be smaller than that in cats, a flat angulation of the needle when approaching the epidural space and an orientation of the needle bevel (angle of the cut in the metal) towards the spinal canal may effectively reduce the aforementioned risks. ...
... 32 In cats, the use of 22-G spinal needles to perform epidural injections may lead to an unsuccessful epidural block, dural laceration or inadvertent intrathecal injection as the eye of the spinal needle is wider than the dorsal epidural space. 32 Since the dorsal epidural space in rabbits may be smaller than that in cats, a flat angulation of the needle when approaching the epidural space and an orientation of the needle bevel (angle of the cut in the metal) towards the spinal canal may effectively reduce the aforementioned risks. The collapse of the dural sac and epidural space enlargement during injection were considered a positive sign of epidural administration of the drugs according to the previous study. ...
... The collapse of the dural sac and epidural space enlargement during injection were considered a positive sign of epidural administration of the drugs according to the previous study. 32 Postoperative gastrointestinal ileus is more likely to be secondary to pain than morphine in rabbits. 12 If ileus is present, early detection and treatment should not be delayed. ...
A healthy 2‐year‐old entire female domestic dwarf rabbit (Oryctolagus cuniculus) was referred for ovariohysterectomy. The premedication included subcutaneous 3 mg/kg ketamine, 1 mg/kg midazolam and 0.05 mg/kg medetomidine. A CT scan was performed under sedation to assess the lumbosacral region. Anaesthesia was induced with propofol (total dose of 10 mg/kg) and maintained with isoflurane in a mixture of oxygen and medical air administered through a supraglottic airway device. Under anaesthesia and prior to the ovariohysterectomy, an ultrasound‐guided epidural was performed administering 0.1 mg/kg preservative free morphine and 0.35 per cent (2.4 mg/kg) bupivacaine as part of the multimodal analgesic approach. Haemodynamic stability with no signs of hypotension, bradycardia or hypoventilation were observed under anaesthesia. Meloxicam (0.5 mg/kg) and buprenorphine (0.03 mg/kg) were administered during the postoperative period. A smooth and uneventful anaesthesia, recovery and hospitalisation period were achieved. Ultrasound‐guided epidural administration of drugs could be applied in similar cases.
... Epidural and spinal anaesthesia are commonly used to control nociception and postoperative pain (OTERO et al., 2016). In veterinary medicine, spinal anaesthesia is still rarely performed, especially in cats. ...
... During puncture, the need traverses the skin and the yellow ligament, and a loss of resistance is perceived. There is risk of inadvertent subarachnoid injection, leading to severe hypotension, cardiovascular collapse, and death (OTERO et al., 2016). The purpose our study was to evaluate the lumbosacral region using ultrasonography (US) and to describe the epidural and subarachnoid spaces to provide a better understanding of neuraxial anaesthesia in cats. ...
... The anatomy of the lumbosacral region in felines is well described in the literature (CAMPOY; READ, 2013). However, ultrasonographic guidance for neuroaxial blocks is a recent development in veterinary medicine (OTERO et al., 2016;CREDIE;LUNA, 2018). ...
... This contrasts with the high proportion of grade IIb breaches at L6 and even more at L7, which are more likely to be associated with neurological problems (Samer et al. 2021). In grade IIb breaches, the entire diameter of the screw is within the vertebral canal and the narrow epidural space, and in this region in the cat (0.04-0.2 mm) is likely insufficient to protect the spinal cord against damage by the screw (Otero et al. 2016). ...
Aims:
To assess the feasibility and safety of a locking cortical pearl plate system for the repair of lumbar vertebral fractures and luxation in cats using an ex vivo feline model.
Methods:
This cadaveric study of the lumbar vertebral column (L1–L7) involved 28 Domestic Short-hair cats without vertebral column pathology. Surrounding soft tissue was removed, except for the paravertebral musculature, joint capsules, and ligaments associated with the L1–L7 vertebrae. To determine whether the application of a 2.0-mm, 69-mm-long, 12-hole locking cortical pearl plate (LCPP) and screws was feasible, the dimensions of the feline lumbar vertebral bodies (length, width, and height) were measured using CT imaging. Width and height were evaluated at five locations along the length of the vertebrae with implant corridors (cor 1–cor4) located in between. Following CT, plates were applied to the vertebral columns. After implantation, another CT scan was performed to evaluate plate positions, screw trajectories, screw implantation angles, and vertebral canal breaching. Implantation was classified according to the modified Zdichavsky scoring system for vertebral canal penetration and grade I and IIa defined as acceptable.
Results:
A total of 371 screws were inserted into the lumbar vertebral bodies, and breaching occurred in 32 cases (8.6%), of which 29 (90.6%) were at L6 and L7. The median angle of inserted screws was 61.6° (min 53.4°, max 76.3°). Aside from one location, no significant angle deviations were observed between breaching (median 62.8°; min 53.4°, max 76.3°) and non-breaching (median 61.2°; min 53.8°, max 74.7°) screws. All 267 screws implanted in L1–L5 were graded I or IIa (acceptable). In contrast, low rates of acceptable implantation were achieved for L6 (52/60; 86.7%) and L7 (24/44; 54.4%), caused by clustering of breachings in corridor 3 of the two vertebrae.
Conclusions:
Application of the LCPP immediately proximal to the transverse processes and ventral to the pedicles with a screw implantation angle of 60° is feasible and appears safe for L1–L5, resulting in a low number of vertebral canal breaches and a high rate of acceptable implantations.
Clinical relevance:
The 2.0-mm, 69-mm-long, 12-hole LCPP can be considered an acceptable option for treating feline vertebral fractures and luxations of L1–L5. It cannot be recommended for use in corridor 3 of L6 or L7 due to the high risk of breaching the vertebral canal.
... Confirmation of the correct execution of the technique is not solely based on the absence of needle resistance. Other methodologies such as ultrasound, neurolocators, contrast administration in the epidural space, and the absence of cerebrospinal fluid in the epidural needle have been employed for verification [17][18][19]. Owing to the unavailability of a neurolocator and the inadequacy of the ultrasound device probe for the size of the animals, the last two techniques were utilized to identify the epidural space and confirm the deposition of the drug and contrast agent, thereby including the animals in our study. ...
Simple Summary
We evaluated the analgesic and postoperative effects of epidurally administered opioids and local anesthetics in 20 cats that underwent elective ovariohysterectomy (OH). Propofol was used as the general anesthetic. The animals were divided into three groups according to the dose of the epidurally administered morphine. Therefore, it was necessary to use fentanyl to complement analgesia in all groups. Postoperatively, 83%, 28%, and 7% of the animals without morphine administration, with a lower dose of morphine, and with a higher dose of morphine, respectively, required additional analgesia. In conclusion, in cats undergoing OH, epidural morphine at the doses used did not eliminate the need for intraoperative rescue analgesia but did reduce the need for postoperative analgesia.
Abstract
Opioids are administered epidurally (PV) to provide trans- and postoperative analgesia. Twenty healthy female cats aged between 6 and 24 months and weighing between 2 and 3.7 kg, undergoing elective ovariohysterectomy (OVH), were induced with propofol (8 mg/kg), followed by continuous infusion (0.1–0.4 mg/kg/min). Three groups were defined: CG (0.1 mL/kg of iodinated contrast, n = 6), G0.1 (0.1 mg/kg of morphine, n = 7), and G0.2 (0.2 mg/kg of morphine, n = 7) per VP. All received 0.1 mL/kg of iodinated contrast per VP and injection water to obtain a total of 0.3 mL/kg. Heart rate (HR), systolic blood pressure (SBP), temperature, expired CO2, oxygen saturation, and number of rescue analgesics were monitored. Postoperatively, a multidimensional scale was used to assess acute pain in cats for 12 h. The mean HR and SBP in the CG were higher at the time of maximum noxious stimulation and required fentanyl in all groups. Postoperatively, 83%, 28%, and 7% of the animals in CG, G0.1, and G0.2, respectively, received rescue analgesia. In cats undergoing OVH, epidural morphine at doses of 0.1 and 0.2 mg/kg did not prevent the need for intraoperative rescue analgesia but reduced the postoperative analgesic needed.
... This anatomical feature contributes to a greater complication rate with lumbosacral epidural procedures [17], including issues such as meningeal piercing or inadvertent subarachnoid injection [17]. Given that the spinal cord in cats does not extend to the sacrococcygeal space, opting for a sacrococcygeal epidural injection may present a potentially safer alternative to the lumbosacral epidural approach [24,27]. ...
This study aimed to provide information about the conus medullaris (CM) and dural sac (DS) termination points in sheep. Thirteen adult Merino-mixed sheep were anaesthetised and underwent lumbosacral computed tomography (CT) myelography. A spinal injection was administered using a Tuohy needle while the sheep were in sternal recumbency. After confirming the presence of cerebrospinal fluid, 0.4 ml kg-1 iodinated contrast media was injected, and a CT scan was conducted. The analysis focused on determining the vertebrae at which the CM and DS ended. The results showed that in eight cases, the conus ended at the first sacral vertebra, while in five sheep, the termination point was identified at the level of the second sacral vertebra. DS termination occurred in the 3rd sacral vertebra in one animal, the 4th sacral vertebra in another sheep, the 1st caudal vertebra in six cases, and the 2nd caudal vertebra in five cases. The findings highlight the need for caution during lumbosacral injections in sheep, as the CM concludes caudally to this space. It is also essential to be aware that the DS persists caudal to the sacrococcygeal space for safe epidural injections in this region.
... As an important channel, the influence of the dura mater in epidural anesthesia is worthy of further study. Although ultrasound imaging of the lumbar spine cannot be used to determine the volume of CSF, it does allow the assessment of certain dimensions of the lumbar dural sac [7]. ...
Background:
The anatomical dimensions of the lumbar dural sac determine the sensory block level of spinal anesthesia; however, whether they show the same predictive value during continuous epidural anesthesia (CEA) remains undetermined. We designed the present study to verify the efficacy of the anatomical dimensions of the lumbar dural sac in predicting the sensory block level during labor analgesia.
Methods:
A total of 122 parturients with singleton pregnancies requesting labor analgesia were included in this study. The lumbar dural sac diameter (DSD), lumbar dural sac length (DSL), lumbar dural sac surface area (DSA), and lumbar dural sac volume (DSV) were measured with an ultrasound color Doppler diagnostic apparatus. CEA was performed at the L2-L3 interspace. After epidural cannulation, an electronic infusion pump containing 0.08% ropivacaine and sufentanil 0.4 μg/ml was connected. The sensory block level was determined with alcohol-soaked cotton, a cotton swab, and a pinprick. The analgesic efficacy of CEA was determined with a visual analog scale (VAS). The parturients were divided into two groups, "ideal analgesia" and "nonideal analgesia," and the groups were compared by t test. Pearson's correlation was performed to evaluate the association between the anatomical dimensions of the lumbar dural sac and sensory block level. Multiple linear regression analysis was used to create a model for predicting the sensory block level.
Results:
In the ideal analgesia group, the height, DSL, DSA, DSV and DSD were significantly smaller, and the body mass index (BMI) was significantly larger (P < 0.05). In addition, the DSL demonstrated the strongest correlation with the peak level of pain block (r = - 0.816, P < 0.0001; Fig. 2A), temperature block (r = - 0.874, P < 0.0001; Fig. 3A) and tactile block (r = - 0.727, P < 0.0001; Fig. 4A). Finally, the multiple linear regression analysis revealed that DSL and BMI contributed to predicting the peak sensory block level.
Conclusion:
In conclusion, our study shows that the sensory block level of CEA is higher when the DSL, DSA, DSV and DSD of puerperae are lower. DSL and BMI can be treated as predictors of the peak sensory block level in CEA during labor analgesia.
... The nerve stimulation test (NS) has been used to identify the epidural space at the SCo intervertebral space in cats (Otero et al. 2015(Otero et al. , 2016 and dogs (Otero & Campoy 2013). This test relies on the electrical stimulation of the plexus caudalis [coccygeus] dorsalis and ventralis giving a characteristic lateral twitch of the tail without perineal or tail base involvement (Otero et al. 2015). ...
Objectives
To evaluate the use of 0.7 mA as a fixed electrical current to indicate epidural needle placement and to confirm that 0.7 mA is greater than the upper limit of the minimal electrical threshold (MET) for sacrococcygeal epidural needle placement in dogs.
Study design
Prospective clinical study.
Animals
A group of 20 client-owned dogs.
Methods
During general anaesthesia and with standard monitoring, the presence of the patellar reflex was confirmed in all dogs. An insulated needle was inserted through the sacrococcygeal intervertebral junction and absence of tail movement was confirmed when a fixed electrical current of 0.7 mA was applied. Then, the needle was further advanced towards the epidural space until the expected motor response was obtained – the 'nerve stimulation test' (NST). The NST was considered positive when a motor response of the muscles of the tail was elicited but not the perineal muscles, whereas it was considered negative when no movement of the tail was evoked. The electrical current was turned to 0 mA and then increased by 0.01 mA increments until tail movement was evoked, this was recorded as the MET. In the positive NST cases, 0.05 mL cm⁻¹ occipitococcygeal length of 2% lidocaine or 0.25-0.5% bupivacaine was administered. Epidural blockade was confirmed by the loss of patellar reflex. Descriptive statistics were used to present data.
Results
Sacrococcygeal epidural needle placement, corroborated by loss of the patellar reflex, was correctly predicted in 89.5% (95% confidence interval: 68.6%-97.1%) of the cases. The MET was 0.22 mA (0.11-0.36).
Conclusions
and clinical relevance A current of 0.7 mA is approximately twice the upper limit of the MET for epidural placement. Therefore, this study demonstrates, with a success rate of 89.5%, the adequacy of using 0.7 mA as the fixed electrical current to detect sacrococcygeal epidural needle placement in dogs.
Correctly identifying the puncture site and needle position in obese dogs can be challenging to achieve epidural anaesthesia. The current study aimed to evaluate a real-time ultrasound-guided technique, to perform epidural anaesthesia in obese or appropriate body condition score dogs, based on visualization of local anaesthetic flow during its injection, compared to the traditional method of palpation of anatomical landmarks. Seventy-two client-owned dogs were evaluated in a prospective, comparative, randomized clinical trial, allocated into four groups of 18 dogs. For the Palpation-guided 1 (PG1) and 2 (PG2) groups, epidural anaesthesia was based on palpating anatomical landmarks. Dogs with a body condition score (BCS) 1-5/9 were included in the PG1 (non-obese), and those with a BCS 6-9/9 in PG2 (obese) groups. In the Ultrasound-guided 1 (USG1 - BCS 1-5/9) and 2 (USG2 – BCS 6-9/9) groups, epidural anaesthesia was guided by ultrasound (US).
The flow of anaesthetic through the epidural canal was observed in all dogs by US. There were fewer needle-to-bone contacts in the US-guided groups when performing epidural anaesthesia; this only occurred on the vertebral laminae, never in the vertebral canal. Ultrasound guidance enabled local anaesthetic injection into the epidural space without the need for palpation of anatomical landmarks to guide needle placement. Blood reflux occurred in 11.1% (PG1), 22.2% (PG2), 5.5% (USG1), and 0% (USG2) of the dogs. Ultrasound-guided punctures led to fewer vascular punctures. Epidural anaesthesia was effective in all animals, and no complications were observed.
Objectives
The aim of this study was to determine the occurrence of dural puncture, indicated by cerebrospinal fluid (CSF) outflow, in cats receiving neuraxial anesthesia through a lumbosacral injection guided by a pop sensation method.
Methods
This was an observational, retrospective study. Cats that were scheduled for lumbosacral neuraxial anesthesia were included. Medical records were analyzed to investigate: (1) demographic data; (2) neuraxial anesthesia performed (epidural/spinal); (3) type of needle used, including gauge and length; (4) presence of CSF (yes/no) and/or blood (yes/no) in the hub of the needle; and (5) flicking of the tail during needle advancement (yes/no).
Results
A total of 94 medical records were analyzed. A 22 G 50 mm Tuohy needle was used in all cats scheduled for an epidural injection (n = 60), whereas a 22 G 40 mm Quincke needle was used in all cats scheduled for an intrathecal injection (n = 34). CSF outflow was detected in 55/60 (91.7%) cats in which a Tuohy needle was used, and 34/34 (100%) of the cats in which a Quincke needle was used ( P = 0.15). Flicking of the tail was detected in 41/60 (68.3%) and in 24/34 (70.6%) injections with Tuohy and Quincke needles, respectively ( P >0.99). Traces of blood, but not active blood outflow, were detected via staining of the first drops of CSF in 2/34 cats in which Quincke needles were used and in none of the cats in which Tuohy needles were used ( P = 0.12).
Conclusions and relevance
This study shows that the lumbosacral approach for neuraxial anesthesia in cats may result in a dural sac puncture when 22 G Quincke or Tuohy needles are used. The pop sensation method should be deemed effective in predicting intrathecal but not epidural needle placement.
Background: The anatomical dimensions of the lumbar dural sac determine the sensory block level of spinal anesthesia; however, whether they show the same predictive value during continuous epidural anesthesia (CEA) remains undetermined. We designed the present study to verify the efficacy of the anatomical dimensions of the lumbar dural sac in predicting the sensory block level during labor analgesia.
Methods: A total of 122 parturients with singleton pregnancies requesting labor analgesia were included in this study. The lumbar dural sac diameter (DSD), lumbar dural sac length (DSL), lumbar dural sac surface area (DSA) , and lumbar dural sac volume (DSV) were measured with an ultrasound color Doppler diagnostic apparatus. CEA was performed at the L2-L3 interspace. After epidural cannulation, an electronic infusion pump containing 0.08% ropivacaine and sufentanil 0.4 µg/ml was connected. The sensory block level was determined with alcohol-soaked cotton, a cotton swab, and a pinprick. The analgesic efficacy of CEA was determined with a visual analog scale (VAS). Divided the parturients into two groups: "ideal analgesia" and "non-ideal analgesia", and compared the groups by t test. Pearson's correlation was performed to evaluate the association between the anatomical dimensions of the lumbar dural sac and sensory block level. Multiple linear regression analysis was used to create a model for predicting the sensory block level.
Results: In the "ideal analgesia" group, the height, DSL, DSA, DSV and DSD were significantly smaller, and the BMI was significantly larger (P<0.05) (Table 1). In addition, the DSL demonstrated the strongest correlation with the peak level of pain block (r=-0.816, P<0.0001; Figure 2A), temperature block (r=-0.874, P<0.0001; Figure 3A) and tactile block (r=-0.727, P<0.0001; Figure 4A). Finally, multiple linear regression analysis revealed that the DSL and BMI contributed to predicting the peak sensory block level.
Conclusion: In conclusion, our study shows that the sensory block level of CEA is higher when the DSL, DSA, DSV and DSD of puerpera are lower. The DSL and BMI can be treated as predictors of the peak sensory block level in CEA during labor analgesia.
Ultrasound allows differentiation of the bony structures and the contents of the spinal canal, such as ligaments, meninges, spinal cord, and nerve roots. Additionally, it is useful to determine the path and depth of needle introduction. This chapter identifies regional anatomy of the vertebral column and also identifies the contents of the spinal canal. In order to obtain an adequate ultrasound image of the vertebral canal, the ultrasound beam needs to reach the vertebral canal from dorsal to ventral, regardless of the probe position. This approach allows the identification of two parallel hyperechoic (bright white) lines flanked by an acoustic shadow produced by the high impedance of the surrounding bones. A longitudinal ultrasound scan of the vertebral column allows identification of the intervertebral level and direction of the needle when an in‐plane neuraxial blockade is performed.
Objective
To investigate the efficacy and safety of the caudal epidural technique in cats with urethral obstruction (UO).
Design
Prospective, double‐blinded, randomized, sham‐controlled study.
Animals
Eighty‐eight male cats with UO.
Interventions
Thirty cats randomized to bupivacaine epidural (BUP), 28 cats to bupivacaine‐morphine epidural (BUP/MOR), and 30 cats to sham epidural (SHAM).
Measurements and Main Results
Time to perform the epidural and efficacy of the epidural was assessed by evaluation of tail and perineal responses. The amount of propofol for urinary catheterization and time to administration of rescue analgesia (buprenorphine) was recorded. Cats were monitored for epidural complications. The median time to perform the epidural was 2 min (range, 0.2‐13 min and range, 0.5‐13 min), with an epidural success rate of 70%. The median amount of propofol administered for urinary catheterization was significantly less in the BUP (2.1 mg/kg; range, 0‐7.5 mg/kg) and MOR/BUP cats (1.85 mg/kg; range, 0‐8.6 mg/kg) as compared to SHAM cats (4 mg/kg; range, 0‐12.7 mg/kg) (P = 0.006, P = 0.0008, respectively). The median time to administration of rescue analgesia was also significantly longer in the BUP (10 h; range, 2‐32 h) and MOR/BUP cats (10 h; range, 4‐45 h) as compared to SHAM cats (4 h; range, 2‐36 h) (P = 0.0026, P = 0.0004, respectively). There were no recognized complications related to the epidural.
Conclusion
Caudal epidural appears to be safe, may reduce the amount of IV anesthesia needed to facilitate urinary catheterization, and can be used to provide long‐term analgesia in the hospital.
Objective
To compare between the nerve stimulation test (group NS) and running-drip method (group RUN) for successful identification of the sacrococcygeal (SCo) epidural space prior to drug administration in dogs.
Animals
A total of 62 dogs.
Study design
A randomized clinical study.
Methods
Dogs requiring an epidural block as part of the multimodal anaesthetic plan were randomly allocated to one of the two study groups. In group NS, the epidural space was located using an insulated needle connected to a nerve stimulator; in group RUN, the epidural space was identified using a Tuohy needle connected to a fluid bag elevated 60 cm above the spine via an administration set. The success of the technique was assessed 5 minutes after epidural injection by the disappearance of the patella reflex. Data were checked for normality, nonparametric data was analysed using a Mann–Whitney U test and success rate was analysed using a Fisher’s exact test. The significance level was set at p < 0.05, and the results are presented in absolute values, percentage (95% confident interval) and median (range).
Results
The success in identification of the epidural space did not differ between groups NS and RUN [87.1% (70.2%–96.4%) versus 90.3% (74.2%–98%); p = 1.000]. The time required for identification of the epidural space was shorter in group RUN [26 (15–53) seconds] than in group NS [40 (19–137) seconds] (p = 0.0225). No other differences were found in any studied variables.
Conclusion
and clinical relevance In this study, both RUN and NS techniques were successful in identifying the epidural space at the SCo intervertebral space. RUN requires no specialised equipment, can be performed rapidly and offers an alternative to the NS for use in general veterinary practice.
Epidural anaesthesia-analgesia (EAA) is a technique employed commonly in human anaesthesia to provide optimum conditions for invasive orthopaedic and soft tissue surgery. Its current use in veterinary practice is comparatively less frequent. Cited reasons for its limited use include lack of confidence in performing the procedure, limited information on the benefits, and limited information on potential complications. The EAA technique, while initially challenging, is an acquirable skill with limited equipment requirements. Use of EAA reduces the degree of surgical stimulation perceived by the patient; this reduction in painful stimulus reduces the required depth of anaesthesia and reduces the quantity of analgesia needed to provide stable anaesthesia. The side-effects of anaesthesia are, as a result, also reduced. In addition to stable intraoperative anaesthesia, EAA provides postoperative patient comfort, which directly reduces systemic analgesia requirements and thus length of hospitalisation. Furthermore, improvement in wound healing and attenuation of cancer progression are reported benefits of EAA. Epidural anaesthesia-analgesia is a minimally invasive technique, despite which number of complications may occur; however, these events are treatable and should not prevent clinicians from incorporating EAA in their perioperative pain management plans. The purpose of this review is to explain the technique, detail the considerations surrounding the practice and summarise the complications reported to date in the literature.
Ultrasonography of the lumbosacral and sacrococcygeal spine is described in cats to confirm effective distribution of local anesthetics injected in the sacrococcygeal epidural space. Ultrasound was used to identify the structures of the spinal canal, local anesthetic flow, and to measure the distances between skin and ligamentum flavum.
Despite caudal blockade being the most widely used regional anaesthetic procedure for infants and children undergoing subumbilical surgery, the question whether the injection velocity of the local anaesthetic itself affects its spread in the epidural space has not yet been investigated. Thus, the aim of the present study was to measure the cranial spread of caudally administered local anaesthetics in infants and children by means of real-time ultrasonography, with a special focus on comparing the effect of using two different speeds of injection.
Fifty ASA I-II infants and children, aged up to 6 yr, weighing up to 25 kg, undergoing subumbilical surgery, were enrolled in this prospective, randomized, observer-blinded study. Caudal blockade was performed under ultrasound observation using ropivacaine 1 ml kg(-1) 0.2% or 0.35% and an injection given at either 0.25 ml s(-1) or 0.5 ml s(-1), respectively.
Ultrasound observation of the local anaesthetic flow and the extent of cranial spread was possible in all patients. All caudal blocks were considered successful, and all surgical procedures could be completed without any indications of insufficient analgesia. No statistically significant difference could be observed between the two injection speeds regarding the cranial spread of the local anaesthetic in the epidural space.
The main finding of the present study is that the speed of injection of the local anaesthetic does not affect its cranial spread during caudal blockade in infants and children. Therefore, the prediction of the cranial spread of the local anaesthetic, depending on the injection speed, is not possible.
Redistribution and secondary spread after the initial injection of local anaesthetics (LAs) are important factors that contribute to the final spread of caudal block in children. However, to date, these phenomena have yet not been studied in detail. Thus, the aim of this observational study was to define patterns of secondary spread and redistribution of a caudal block by means of real-time ultrasonography scanning and cutaneous testing.
Ultrasound assessment of LA spread within the caudal-epidural space and epidural pressure was followed during 15 min after initial injection (1.5 ml kg(-1), ropivacaine 0.2%) in 16 infants. At 15 min post-injection, cutaneous testing was also performed to assess the cranial dermatomal level of the block (at end-tidal sevoflurane 2.5%).
The median ultrasound-assessed cranial spread was Th10 and Th8 at 0 and 15 min, respectively, and the sensory level at 15 min was Th4. The caudal injection was initially found to compress the terminal part of the dural sac, later followed by a partial re-expansion as epidural pressure was returning towards pre-injection values. An intrasegmental redistribution from the dorsal to the ventral compartment of the epidural space was also observed.
Two separate patterns of secondary spread of caudal block could be observed, being horizontal intrasegmental redistribution and longitudinal cranial spread. The observed bi-directional movement of cerebrospinal fluid (coined 'the CSF rebound mechanism') does explain a major part of the difference between the initial ultrasound-assessed cranial level and the final level determined by cutaneous testing.
Current methods of locating the epidural space rely on surface anatomical landmarks and loss-of-resistance (LOR). We are not aware of any data describing real-time ultrasound (US)-guided epidural access in adults.
We evaluated the feasibility of performing real-time US-guided paramedian epidural access with the epidural needle inserted in the plane of the US beam in 15 adults who were undergoing groin or lower limb surgery under an epidural or combined spinal-epidural anaesthesia.
The epidural space was successfully identified in 14 of 15 (93.3%) patients in 1 (1-3) attempt using the technique described. There was a failure to locate the epidural space in one elderly man. In 8 of 15 (53.3%) patients, studied neuraxial changes, that is, anterior displacement of the posterior dura and widening of the posterior epidural space, were seen immediately after entry of the Tuohy needle and expulsion of the pressurized saline from the LOR syringe into the epidural space at the level of needle insertion. Compression of the thecal sac was also seen in two of these patients. There were no inadvertent dural punctures or complications directly related to the technique described. Anaesthesia adequate for surgery developed in all patients after the initial spinal or epidural injection and recovery from the epidural or spinal anaesthesia was also uneventful.
We have demonstrated the successful use of real-time US guidance in combination with LOR to saline for paramedian epidural access with the epidural needle inserted in the plane of the US beam.
Correct caudal cannula placement is essential for block success and the avoidance of complications. The aim of this study was to assess the use of a saline injection test bolus with ultrasound (US) imaging to identify correct cannula placement for caudal anesthesia.
A prospective observational study of 60 children undergoing caudal anesthesia. A Sonosite 180 Plus (Sonosite Inc., Bothwell, WA) was used to image the spine and look for caudal space expansion secondary to saline injection.
Saline test bolus correctly identified position in 96.5% of all subjects, and was 100% successful in children under 2 years of age.
These preliminary results suggest saline test bolus under US imaging is a reliable indicator of correct cannula position for caudal block. We found it safe, quick to perform, and provided additional useful information.
Drug access to the site of action is largely dependent on the drug's physical and chemical properties and its interaction with the different membranes that cover and protect the nervous tissue. Sound anatomic knowledge and an understanding of the effects of drug selection are essential for the safe implementation of these techniques. The degree of sympathetic nerve blockade caused by spinal or epidural anesthesia is directly related to the anatomic extent of the block. Surgical trauma typically produces a localized inflammatory response, a systemic neuroendocrine response, and activation of somatic and visceral afferent nerve fibers. To perform an epidural injection, the animal may be placed in either sternal or lateral recumbency, depending on the patient's medical condition and the clinician's preference. Several methods have been developed for confirming needle placement in the epidural space including: loss of resistance (LOR), use of a 'hanging drop,' and electrostimulation.
A 16-year-old castrated male cat underwent general anaesthesia twice within three weeks for perineal urethrostomy and its surgical revision. The cat was affected by compensated hyperthrophic cardiomyopathy. The first anaesthesia was uneventful; in the second anaesthesia a lumbosacral spinal injection of bupivacaine 0.5 per cent was carried out during inhalant anaesthesia. Immediately after completion of injection, respiratory arrest, bilateral mydriasis and cardiovascular collapse occurred. Supportive measures restored normotension and normal cardiac rhythm. Inhalation of isoflurane was immediately interrupted after respiratory arrest. Nevertheless, the cat remained comatose for two hours and it was transferred to the intensive care unit under oxygen supplementation by mask once responsive to visual stimuli. Twenty-four hours later, neurological exam did not reveal any deficit and the cat recovered completely.
Epidural injections are commonly performed blindly in veterinary medicine. The aims of this study were to describe the lumbosacral ultrasonographic anatomy and to assess the feasibility of an ultrasound-guided epidural injection technique in dogs. A cross sectional anatomic atlas of the lumbosacral region and ex vivo ultrasound images were obtained in two cadavers to describe the ultrasound anatomy and to identify the landmarks. Sixteen normal weight canine cadavers were used to establish two variations of the technique for direct ultrasound-guided injection, using spinal needles or epidural catheters. The technique was finally performed in two normal weight cadavers, in two overweight cadavers and in five live dogs with radiographic abnormalities resulting of the lumbosacral spine. Contrast medium was injected and CT was used to assess the success of the injection. The anatomic landmarks to carry out the procedure were the seventh lumbar vertebra, the iliac wings, and the first sacral vertebra. The target for directing the needle was the trapezoid-shaped echogenic zone between the contiguous articular facets of the lumbosacral vertebral canal visualized in a parasagittal plane. The spinal needle or epidural catheter was inserted in a 45° craniodorsal–caudoventral direction through the subcutaneous tissue and the interarcuate ligament until reaching the epidural space. CT examination confirmed the presence of contrast medium in the epidural space in 25/25 dogs, although a variable contamination of the subarachnoid space was also noted. Findings indicated that this ultrasound-guided epidural injection technique is feasible for normal weight and overweight dogs, with and without radiographic abnormalities of the spine.
Sacrococcygeal epidural anaesthesia allows selective desensitisation of the sacral plexus. Ultrasound is used for guidance in human anaesthesia to facilitate sacrococcygeal epidural injections. The aims of this study were to describe the sonographic appearance of the sacrococcygeal region in dogs and a technique for performing epidural injection at this location under ultrasound guidance. In the preliminary part of the study four cadavers were used to describe the sonoanatomy of the sacrococcygeal space and to develop the ultrasound-guided puncture technique. In the second phase of the study this technique was repeated in four dogs under general anaesthesia. In all dogs the sacrococcygeal space appeared as a circular hypoechoic region, located caudal to the sacral caudal articular processes, delimited by bony hyperechoic structures such as body and arch of the first caudal vertebra. Ultrasound guidance allowed the operator to visualise and position the spinal needle into the sacrococcygeal epidural space. No complications were reported during this procedure. Preliminary results indicate that ultrasound-guided sacrococcygeal epidural anaesthesia may be considered as an alternative to a blind approach technique.
Objective
To determine if a nerve stimulation test (NST) could act as a monitoring technique to confirm sacrococcygeal epidural needle placement in cats.Study designProspective experimental trial in a clinical setting.AnimalsTwenty-four adult cats, scheduled for a therapeutic procedure where epidural anesthesia was indicated.Methods
Under general anesthesia, an insulated needle was inserted through the S3-Cd1 intervertebral space guided by the application of a fixed electrical current (0.7 mA) until a motor response was obtained. The NST was considered positive when the epidural nerve stimulation produced a motor response of the muscles of the tail, whereas it was considered negative when no motor response was evoked. In the NST positive cases, 0.3 mL kg−1 of 0.5% bupivacaine was administrated before needle withdrawal. Ten minutes after injection, epidural blockade was confirmed by the loss of perineal (anal), and pelvic limbs reflexes (patellar and withdrawal).ResultsThe use of a fixed electrical stimulation current of 0.7 mA resulted in correct prediction of sacrococcygeal epidural injection, corroborated by post bupivacaine loss of perineal and pelvic limb reflexes, in 95.8% of the cases.Conclusion and clinical relevanceThis study demonstrates the feasibility of using, in a clinical setting, an electrical stimulation test as an objective and in real-time method to confirm sacrococcygeal epidural needle placement in cats.
Objective
To determine the minimal electrical threshold (MET) necessary to elicit muscle contraction of the pelvic limb or tail when an insulated needle is positioned outside (METout) and inside (METin) the lumbosacral epidural space in cats. Study designProspective, blinded study. AnimalsTwelve mixed-breed healthy adult cats, scheduled for a therapeutic procedure where lumbosacral epidural administration was indicated. Methods
Under general anesthesia, an insulated needle was advanced through tissues of the lumbosacral interspace until its tip was thought to be just dorsal to the interarcuate ligament. An increasing electrical current (0.1 ms, 2 Hz) was applied through the stimulating needle in order to determine the MET necessary to obtain a muscle contraction of the pelvic limb or tail (METout), and then 0.05 mL kg−1 of iohexol was injected. The needle was further advanced until its tip was thought to be in the epidural space. The MET was determined again (METin) and 0.2 mL kg−1 of iohexol was injected. The cats were maintained in sternal position. Contrast medium spread was determined through lateral radiographic projections. ResultsThe radiographic study confirmed the correct needle placement dorsal to the interarcuate ligament in all cats. When the needle was placed ventrally to the interarcuate ligament, iohexol was injected epidurally in ten and intrathecally in two cats. The METout and METin was 1.76 ± 0.34 mA and 0.34 ± 0.07 mA, respectively (p < 0.0001). Conclusion and clinical relevanceNerve stimulation can be employed as a tool to determine penetration of the interarcuate ligament but not the piercing of the dura mater at the lumbosacral space in cats.
Background:
Color flow Doppler ultrasonography has been used to confirm caudal epidural injection, but its ability to detect accidental intrathecal injection is unknown. We hypothesized that, when using color flow Doppler, the injection of fluid into the epidural space would result in turbulent flow which would appear as a burst of color while intrathecal injection would show an absence of a color flow Doppler signal.
Methods:
Two groups of pediatric patients (up to 6 years of age) were prospectively enrolled for this observational study during a 2-month period. One group (group E) consisted of patients suitable for elective surgery using caudal epidural analgesia, and the other (group I) included patients receiving lumbar puncture for intrathecal chemotherapeutic injection. After induction of general anesthesia and placement of the patient in the lateral position, an 8 MHz curved array probe (Sonosite TITAN, Bothell, WA) was applied to obtain a transverse image of the lumbar region (L1-L3). Real-time images using color flow Doppler were obtained and recorded during initial injections of 2 consecutive (20 seconds apart) aliquots of 0.1 mL/kg medication of local anesthetic (0.25% bupivacaine) or chemotherapy drugs (mixture of methotrexate, cytarabine, and hydrocortisone) at a rate of 0.5 to 1.0 mL/s. After obtaining the study images, the rest of the medication was injected in standard fashion. A blinded anesthesiologist later evaluated the recorded images to determine a positive or negative result (positive = presence of turbulence as illustrated by a medley of color; negative = no turbulence or color). Sensitivity, specificity, and positive and negative predictive values were calculated for those patients who had successful analgesia (group E) and intrathecal (group I) injections.
Results:
Forty recorded images from 41 patients (group E, n = 21; group I, n = 20) were included in the analysis. The observed sensitivity, specificity, positive predictive value, and negative predictive values were all 100%. The lower 95% confidence limits were 0.832.
Conclusion:
In the context of this study, color flow Doppler could differentiate epidural from intrathecal injection into the caudal space of children up to 6 years of age using a 0.1 mL/kg injection volume and injection rate of 0.5 to 1.0 mL/s.
The role of ultrasound in central neuraxial blockade has been underappreciated, partly because of the relative efficacy of the landmark-guided technique and partly because of the perceived difficulty in imaging through the narrow acoustic windows produced by the bony framework of the spine. However, this also is the basis for the utility of ultrasound: an interlaminar window that permits passage of sound waves into the vertebral canal also will permit passage of a needle. In addition, ultrasound aids in identification of intervertebral levels, estimation of the depth to epidural and intrathecal spaces, and location of important landmarks, including the midline and interlaminar spaces. This can facilitate neuraxial blockade, particularly in patients with difficult surface anatomic landmarks. In this review article, the authors summarize the current literature, describe the key ultrasonographic views, and propose a systematic approach to ultrasound imaging for the performance of spinal and epidural anesthesia in the adult patient.
To refine and test construct validity and reliability of a composite pain scale for use in assessing acute postoperative pain in cats undergoing ovariohysterectomy.
40 cats that underwent ovariohysterectomy in a previous study.
In a previous randomized, double-blind, placebo-controlled study, a composite pain scale was developed to assess postoperative pain in cats that received a placebo or an analgesic (tramadol, vedaprofen, or tramadol-vedaprofen combination). In the present study, the scale was refined via item analysis (distribution frequency and occurrence), a nonparametric ANOVA, and item-to-total score correlation. Construct validity was assessed via factor analysis and known-groups discrimination, and reliability was measured by assessing internal consistency.
Respiratory rate and respiratory pattern were rejected after item analysis. Factor analysis resulted in 5 dimensions (F1 [psychomotor change], posture, comfort, activity, mental status, and miscellaneous behaviors; F2 [protection of wound area], reaction to palpation of the surgical wound and palpation of the abdomen and flank; F3 [physiologic variables], systolic arterial blood pressure and appetite; F4 [vocal expression of pain], vocalization; and F5 [heart rate]). Internal consistency was excellent for the overall scale and for F1, F2, and F3; very good for F4; and unacceptable for F5. Except for heart rate, the identified factors and scale total score could be used to detect differences between the analgesic and placebo groups and differences among the analgesic treatments.
Results provided initial evidence of construct validity and reliability of a multidimensional composite tool for use in assessing acute postoperative pain in cats undergoing ovariohysterectomy.
Subarachnoid lumbar puncture is used commonly in the dog for cerebrospinal fluid collection and/or myelography. Here in we describe the percutaneous ultrasound anatomy of the lumbar region in the dog and a technique for ultrasound-guided lumbar puncture. Ultrasound images obtained ex vivo and in vivo were compared with anatomic sections and used to identify the landmarks for ultrasound-guided lumbar puncture. The ultrasound-guided procedure was established in cadavers and then applied in vivo in eight dogs. The anatomic landmarks for the ultrasound-guided puncture, which should be identified on the parasagittal oblique ultrasound image are the articular processes of the fifth and sixth lumbar vertebrae and the interarcuate space. The spinal needle is directed under ultrasound-guidance toward the triangular space located between the contiguous articular processes of the fifth and sixth lumbar vertebrae and then advanced to enter the vertebral canal. Using these precise ultrasound anatomic landmarks, an ultrasound-guided technique for lumbar puncture is applicable in the dog.
Current knowledge of drugs administered epidurally has allowed an effective way of providing analgesia for a wide variety of conditions in veterinary patients. Proper selection of drugs and dosages can result in analgesia of specific segments of the spinal cord with minimal side effects. Epidural anesthesia is an alternative to general anesthesia with inhalation anesthetics, although the combination of both techniques is more common and allows for reduced doses of drugs used with each technique. Epidural anesthesia and intravenous anesthetics can also be used without inhalation anesthetics in surgical procedures caudal to the diaphragm.
The aim of this work was to investigate the postnatal development of the feline spinal cord. Our study showed that the main period of growth leading to the cervical and lumbar enlargements begins after birth and is completed at the age of 5–6 months. Comparing the relationship between the length of the spinal cord and the vertebral column, we found that in contrast to the adult cat, in the newborn cat, length, area and volume of segments show similar values along the spinal cord. This also applied to the length of the vertebrae.
Due to a heterogeneous growth, not all segments of the spinal cord end up situated cranial to their corresponding vertebrae. As a consequence, the end of the conus medullaris is still located within the sacral canal in animals older than 2 months. These findings strongly propose that injections into the vertebral canal of the cat have to be performed caudal to the sacral vertebrae.
A brief outline of the history of epidural analgesia is followed by a review of the anatomy of the epidural space with particular reference to epidural block. The technique of epidural injection in the dog is described as are the indications for the technique. These include the provision of anaesthesia for such procedures as orthopaedic surgery of the hind limb and caesarian section. The cardiovascular effects of epidural block are discussed and suggestions are made for the prevention of hypotension. The various drugs and their combinations which may be used for epidural administration are outlined. The commonest used local anaesthetic agents are bupivacaine and lidocaine. Epidural administration of opioid drugs is a relatively new technique which is used to provide intra- and post-operative analgesia. Morphine is the drug of choice for this indication. The use of other classes of drugs, such as the alpha 2 agonists and ketamine, are also considered. A variety of side-effects, contra-indications and complications are described together with methods for reducing their incidence and effects.
The aim of the present study was to compare two confirmatory tests - the 'swoosh' test (auscultation during caudal injection) and real time ultrasound imaging (both transverse 2D imaging and color flow Doppler imaging) in pediatric patients receiving a caudal epidural block.
This was a retrospective observational study of caudal injections administered to 83 pediatric patients (0-11 years) presenting for elective surgery over a 4 month time period. While injecting small aliquots of local anesthetic, a standard stethoscope was placed over the lower lumbar spine to auscultate for the 'swoosh' test. An ultrasound machine (Sonosite Titan, Sonosite Inc., Bothell, WA, USA) was then utilized for real-time visualization of caudal injectate. Each test performed during the caudal injection (swoosh, turbulence on 2D imaging, or color flow on Doppler imaging) was recorded as positive, negative or equivocal.
Eighty out of 83 patients (96.4%) had a successful caudal block based on minimal or no perioperative narcotic use, minimal or no response to surgical stimulation, the presence of motor blockade and patient comfort in the PACU. Ultrasound was significantly superior to 'swoosh' for sensitivity (96.3% vs 57.5%), negative predictive (40% vs 5.6 value) % and likelihood ratio (2.89 vs 1.73). Specificity and positive predictive value were not different between 'swoosh' and ultrasound. Of the ultrasound tests, turbulence was more sensitive than color flow Doppler (95.0% vs 78.8%).
Ultrasonography is superior to the 'swoosh' test as an objective confirmatory technique during caudal block placement in children. We found the presence or absence of turbulence during injection within the caudal space to be the best single indicator of caudal success. We think ultrasonography should be used, if available, when teaching this technique.
Diagnostic Ultrasound – Physics and Equipment
- Dudley NJ
Small Animal Regional Anesthesia and Analgesia
- Otero PE
- Campoy L
Spinal Drug Delivery
- Fletcher TF
- Malkmus SA
Lumb & Jones' Veterinary Anaesthesia and Analgesia
- Skarda RT
- Tranquilli WJ
Local and regional anaesthetic and analgesic techniques: cats
- Skarda