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ABSTRACT: To describe the effects of alfaxalone on the canine electroencephalogram (EEG).
Experimental study.
Eight healthy adult Huntaway dogs.
Anaesthesia was induced with propofol and maintained with halothane (0.85-0.95 end-tidal volume %) in oxygen. Animals were ventilated to maintain stable end-tidal CO(2) and halothane concentrations. Following a 30 minute stabilisation period, alfaxalone (0.5 mg kg(-1) ) was infused intravenously over a 5 minute period. The electroencephalogram was recorded from the beginning of the stabilisation period until 60 minutes following the start of alfaxalone treatment. Data were subjected to fast Fourier transformation, and median frequency, 95% spectral edge frequency and total EEG power were calculated. Two-factorial repeated measures anova (time and EEG channels were factors) was used for statistical analysis (p < 0.05).
A shift in the dominant frequency band from beta to delta after alfaxalone treatment and occasional burst suppression were observed. Median frequency decreased significantly below baseline (9.2 ± 1.4 Hz) (mean ± SD) during alfaxalone infusion. The lowest value (4.8 ± 1.2 Hz) was recorded 5 minutes after the start of infusion. Spectral edge frequency also decreased below baseline (26.2 ± 1.5 Hz) and the lowest value (22.6 ± 1.5 Hz) also was detected at 5 minutes after the start of infusion. Total EEG power did not change significantly. In some frequencies EEG power increased soon after the start of alfaxalone infusion, then decreased below baseline later (biphasic pattern).
Alfaxalone induced biphasic changes on EEG and decreased F(50) and F(95) in halothane anaesthetized dogs.
Veterinary Anaesthesia and Analgesia 11/2011; 38(6):529-35. · 0.94 Impact Factor
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ABSTRACT: We investigated the hypothesis that lead poisoning was the cause of the clinical syndrome of clenched feet paralysis and leg paresis in wild raptors. Swamp Harriers (Circus approximans) are one of three extant native raptor species in New Zealand. Harriers with the syndrome were found to have statistically significantly higher blood lead concentrations than those without clenched feet (t-test; t=-4.06, df=5, P=0.01). However, elevated blood lead concentrations were also present in 60% of wild harriers without the clinical syndrome of clenched feet paralysis and leg paresis. There were features of the response to chelation treatment, electroneurodiagnostics, and pathology that were inconsistent with lead poisoning as reported in other birds of prey. We conclude that lead may be a factor in the expression of this clinical syndrome of clenched claw paralysis but that other factors not identified in our study play a role in the expression of the disease.
Journal of wildlife diseases 10/2011; 47(4):907-16. · 1.08 Impact Factor
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ABSTRACT: To report the severe metabolic acidosis identified in a group of 11 healthy mules anaesthetized with halothane for castration.
Data generated from a prospective study.
Eleven mules aged 2.5-8 years, weighing 230-315 kg and 11 horses aged 1.5-3.5 years, weighing 315-480 kg.
Animals were anaesthetized for castration as part of an electroencephalographic study. Preanaesthetic medication was acepromazine (0.03 mg kg(-1) ) administered through a preplaced jugular venous catheter. Anaesthesia was induced 30-90 minutes later with intravenous thiopental (10 mg kg(-1) ). After orotracheal intubation, anaesthesia was maintained with halothane vaporised in oxygen. The animals' lungs were ventilated to maintain the end-tidal CO(2) concentration between 3.9 and 4.5 kPa (29-34 mmHg). Anaesthetic monitoring included invasive blood pressure measurement via the auricular artery (mules) and submandibular branch of the facial artery (horses). Arterial blood gas samples were drawn from these catheters at three time points during surgery and pH, PaCO(2) , base excess (ecf) and were measured. Values were compared between groups using a Mann-Whitney test. p was taken as <0.05. Results are reported as median (range).
PaCO(2) did not differ between groups but pH was significantly lower in mules [7.178 (7.00-7.29)] compared to horses [7.367 (7.24-7.43)] (p=0.0002). values were significantly lower in the mules [16.6 (13.0-22.3) mM] compared to horses [23.7 (20.9-23.7) mM] (p=0.0001), whilst base excess (ecf) was significantly more negative in the mules [-11.4 (-1.27 to -16) mM] compared to horses [-1.3 (-5.8 to +2.4) mM] (p=0.0004).
This study demonstrated severe metabolic acidosis in healthy mules, which may have prompted intervention with drug therapies in a clinical arena. It is probable that the acidosis existed prior to anaesthesia and caused by diet, but other possible causes are considered.
Veterinary Anaesthesia and Analgesia 09/2011; 38(5):484-9. · 0.94 Impact Factor
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ABSTRACT: To investigate the effects of age at castration on the subsequent behavioural response to tail docking.
Randomised prospective blinded experimental study.
Forty-five male lambs were admitted to the study at birth.
The lambs were allocated into two groups for castration by rubber ring at 1 (1D, n = 20) or 10 (10D, n = 25) days of age. Following castration both groups of lambs were tail-docked by rubber ring at between 26 and 34 days of age. Their behavioural responses to tail docking were recorded by video for 30 minutes before (n = 11) and 30 minutes after (n = 45) tail docking. Statistical differences were tested using anova with Mann-Whitney post-hoc testing.
Two data sets were removed resulting in n = 19 and = 24 at 1D and 10D, respectively. A significant increase in the incidence of active and abnormal postural behaviour was seen in both groups after tail docking. Three behaviours were significantly different (p < 0.05) between the two groups. These behaviours were rolling, standing unsteadily and the total proportion of time standing with abnormal posture. These behaviours all had greater incidence in the lambs castrated at 1D of age.
Lambs castrated at 1D appeared to perceive a greater intensity of pain after subsequent tail docking than lambs castrated at 10D.
The timing of a single noxious stimulus in young animals can affect subsequent pain perception.
Veterinary Anaesthesia and Analgesia 07/2010; 37(4):375-81. · 0.94 Impact Factor
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ABSTRACT: To evaluate electroencephalographic (EEG) changes during ovariohysterectomy (OVH) in rats anaesthetized with halothane, and modification of the EEG changes by the co-administration of fentanyl, ketamine or thiopental.
Prospective, randomized, blinded controlled study.
Sixty adult female Sprague-Dawley rats.
Anaesthesia was induced and maintained with halothane [Fe'HAL 0.95 +/- 0.05%]. The electroencephalogram was recorded continuously from the left and right primary somatosensory cortices. Rats were randomly divided into four groups and a rapid IV infusion of physiological saline, thiopental, ketamine or fentanyl was administered. OVH started 10 minutes after drug administration. Blood samples, for assay of plasma drug concentrations, were collected 5 minutes after administration and at the end of surgery. Electroencephalograph descriptors median frequency (F50), spectral edge frequency 95% (F95) and total power (P(tot)), recorded during non-surgical baseline periods, were compared with those recorded during defined surgical periods; skin incision, right and left ovarian pedicle ligation; cervical ligation. Plasma drug concentrations were measured using high performance lipid chromatography.
Although a large number of statistical differences in EEG data were observed, these generally represented a reduction in F50 or F95 throughout the experimental recording period and were similar between groups. A significant reduction in P(tot) occurred during ligation of the ovaries and cervix in the control group compared with other recording periods. The co-administration of ketamine, fentanyl and thiopental obtunded the reduction in P(tot).
Electroencephalographic changes, in the control group, mimicked changes reported in other studies using the minimal anaesthesia model. However, the stability in F50 during the surgical period compared with the baseline period indicated that OVH is an unsuitable surgical stimulus to investigate EEG changes with noxious stimulation. This may be attributed to the relatively prolonged duration of this surgical procedure and the primarily visceral afferent sensory innervation of the genital tract.
Veterinary Anaesthesia and Analgesia 01/2010; 37(1):14-24. · 0.94 Impact Factor
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ABSTRACT: This study compared the efficacy of different classes of analgesics in preventing the changes in electroencephalographic (EEG) indices of nociception in anaesthetised dogs, subjected to a standard electrical stimulus. In a crossover study, eight dogs received morphine (0.5mg/kg) or tramadol (3mg/kg) or parecoxib (1mg/kg) or 0.9% saline subcutaneously (SC) at the time of pre-anaesthetic medication. After induction with intravenous propofol, anaesthesia was maintained with halothane at a stable concentration between 0.85% and 0.95%. EEG was recorded in a three electrode montage, using SC needle electrodes, before and after electrical stimulation of dogs during anaesthesia. Post-stimulation median frequency (a reliable indicator of nociception) of the EEG increased significantly in tramadol, parecoxib and saline groups compared to that of morphine. Total EEG power decreased in all treatment groups following stimulation. These results indicate that the changes in EEG responses to noxious stimulation can be used for evaluating anti-nociceptive efficacy of analgesics.
Research in Veterinary Science 07/2009; 88(1):127-33. · 1.65 Impact Factor
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ABSTRACT: To characterize changes in the cerebro-cortical response of lambs to rubber-ring castration during the first 6 weeks of postnatal life.
Coopworth-Texel cross ram lambs between 3 hours and 44 days of age.
The electroencephalogram (EEG) and heart rate responses to rubber ring castration were compared. Anaesthesia was induced via a face mask and maintained with halothane in oxygen (e'(Hal) = 1.2%). Once a stable plane of anaesthesia had been achieved, data collection of EEG and electrocardiogram (ECG) commenced, and the lambs were castrated 15 minutes later, using rubber rings. Heart rate was derived from the ECG and the median frequency (F(50)), spectral edge frequency (F(95)) and total power (p(tot)) were derived from the EEG.
Castration-induced changes in F(50) increased from 2 +/- 1.8% in the youngest lambs to a maximum of 33 +/- 8.9% in the 36 +/- 0.5 day-old lambs. Changes in F(95) increased from -7 +/- 3% in the youngest lambs to a maximum of 16 +/- 11% in the 36 +/- 0.5 day-old lambs. Linear regression analysis in lambs up to 10 days of age demonstrated a change in the response with age that was significantly different from zero for F(50) (r(2) = 0.28, p = 0.007) and F(95) (r(2) = 0.38, p = 0.001), but not for p(tot) or heart rate.
This study identified significant changes in the responsiveness of the lambs' cerebral cortex to the noxious stimulation of castration over the first 7-10 days of postnatal life. The results suggest that mechanisms that suppress responses of the fetus to noxious stimulation may still be active in the first few days after birth.
This study documents changes in central nociceptive processing which may reflect the ability of neonatal animals to perceive pain.
Veterinary Anaesthesia and Analgesia 06/2009; 36(3):273-9. · 0.94 Impact Factor
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ABSTRACT: To compare the effects of morphine, parecoxib, tramadol and a combination of parecoxib, tramadol and pindolol on nociceptive thresholds in awake animals and their effect on glomerular filtration rate (GFR) in dogs subjected to 30 minutes of anesthesia.
Eight adult mixed breed experimental dogs.
Randomized, controlled trial.
Dogs received 0.05 mg kg(-1) acepromazine subcutaneously (SC) as anaesthetic pre-medication. Thirty to sixty minutes later, they received either tramadol 3 mg kg(-1) intravenously, (IV), parecoxib (1 mg kg(-1) IV), a combination of tramadol 3 mg kg(-1) (IV), parecoxib 1 mg kg(-1) (IV) and pindolol 5 microg kg(-1) (SC), morphine (0.1 mg kg(-1) (IV) or 0.9% saline (2 mL). Anaesthesia was then induced with IV propofol to effect (2.9 +/- 0.8 mg kg(-1)) and maintained with halothane in oxygen for 30 minutes. Systolic arterial blood pressure was maintained above 90 mmHg with IV fluids and by adjusting the inspired halothane concentration. Post-treatment nociceptive thresholds to mechanical stimuli, expressed as percent of pre-treatment values, were compared between the treatments to assess the analgesic efficacy of the drugs. Plasma iohexol clearance (ICL), a measure of GFR, was estimated both before and 24 hours after induction of anaesthesia to study the drugs' effects on renal perfusion. Nociceptive threshold and GFR data were compared using mixed model analysis in SAS 9.1.
Both tramadol and parecoxib produced similar analgesia, which was less than that of morphine. Their combination with pindolol produced analgesia comparable with morphine. None of the test drugs, either alone or in combination, reduced GFR.
Tramadol and parecoxib (either alone or in combination) can increase nociceptive thresholds in awake dogs and have minimal effects on renal perfusion in normotensive dogs subjected to anaesthesia.
Veterinary Anaesthesia and Analgesia 02/2009; 36(1):86-94. · 0.94 Impact Factor
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ABSTRACT: Nonsteroidal antiinflammatory drugs and N-methyl-D-aspartate (NMDA) receptor antagonists reduce pain hypersensitivity when given by the intrathecal (i.t.) route, but their combined effects have hardly been studied. We assessed the effects of the nonsteroidal antiinflammatory drug ketoprofen and the NMDA receptor channel blocker ketamine, given alone and in combination, on mechanical nociceptive thresholds in sheep implanted with indwelling cervical i.t. catheters.
Sheep were given, by i.t. catheter, ketoprofen (200-3200 microM; 100 microL) and ketamine (25-400 microM; 100 microL) alone or in combination (837.95-3350.78 microM; 100 microL; 0.955:0.045 proportion). They also received NMDA (2 mM; 100 microL) preceded by the highest concentration of ketoprofen and ketamine alone or in combination. Saline solution (0.9%; 100 microL) and xylazine (1.95 mM; 100 microL) were used as negative and positive controls, respectively.
Xylazine significantly increased the area under the nociceptive threshold versus time curve values (AUC) for 30, 60, and 180 min posttreatment. Ketoprofen and ketamine, alone and in combination, produced no significant effect on AUC values. NMDA alone decreased the AUC value for 30 min posttreatment. This pain hypersensitivity was prevented by preadministering ketoprofen and ketamine alone and in combination.
In sheep, i.t. administration of ketoprofen and ketamine, alone or together, produced no hypoalgesia; however, they prevented NMDA-induced mechanical hypersensitivity. Ketoprofen and ketamine may have therapeutic potential in conditions associated with persistent pain.
Anesthesia and analgesia 01/2009; 107(6):2061-7. · 3.08 Impact Factor
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ABSTRACT: The study aim was to develop a model to generate cerebral evoked potentials (CEPs) by mechanical distention of the duodenum in rats. Twenty Sprague-Dawley rats were anaesthetized and the EEG recorded from the left and right somatosensory cortices (S1L, S1R). A balloon catheter was implanted into the duodenum. A pneumatic device, triggered by data acquisition software, inflated the balloon for 200 ms every 3s to deliver a repeatable noxious stimulus. EEG was recorded for 100 ms before and 500 ms after onset of inflation and the response to 512 stimuli averaged to generate a CEP. Two CEPs were generated in each animal and data summed to calculate a single CEP for each channel. Data were excluded when the signal to noise ratio was < 2, therefore data are presented from 11 animals. A repeatable CEP was identified in waveforms recorded from S1L. The mean (S.D.) CEP comprised a triphasic waveform (P1, N1, P2) with latencies of 246.0 (24.7), 289.3 (12.8) and 321.5 (13.2)ms, respectively. We are the first group to have generated and characterized a CEP following mechanical stimulation of the duodenum. This model can be applied to further elucidate the mechanisms leading to visceral pain perception.
Journal of Neuroscience Methods 06/2007; 162(1-2):215-21. · 1.98 Impact Factor
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ABSTRACT: To record the electroencephalographic changes during castration in ponies anaesthetized with halothane and given intravenous (IV) lidocaine by infusion. The hypothesis tested was that in ponies, IV lidocaine is antinociceptive and would therefore obtund EEG changes during castration.
Ten Welsh mountain ponies referred to the Department of Clinical Veterinary Medicine, Cambridge for castration under general anaesthesia.
Following pre-anaesthetic medication with intramuscular acepromazine (0.02 mg kg(-1)) anaesthesia was induced with IV guaiphenesin (60 mg kg(-1)) and thiopental (9 mg kg(-1)) and maintained with halothane at an end-tidal concentration (FE'HAL) of 1.2%. A constant rate infusion of IV lidocaine (100 microg kg(-1) minute(-1)) was administered throughout anaesthesia. The electroencephalogram (EEG) was recorded continuously using subcutaneous needle electrodes. All animals were castrated using a closed technique. The raw EEG signal was analysed after completion of each investigation, and the mean values of EEG variables (median frequency, spectral edge frequency, total amplitude) recorded during a baseline period (before surgery began) and the removal of each testicle were compared using anova for repeated measures.
Spectral edge frequency (SEF) 95% decreased during removal of the second testicle compared with baseline recordings. No other significant EEG changes during castration were measured.
Lidocaine obtunded the EEG changes identified during castration in a previous control study, providing indirect evidence that lidocaine administered peri-operatively was antinociceptive and contributed to anaesthesia during castration.
The antinociceptive effect of lidocaine combined with its minimal cardiovascular effects indicate a potential use for systemic lidocaine in clinical anaesthetic techniques.
Veterinary Anaesthesia and Analgesia 08/2005; 32(4):212-21. · 0.94 Impact Factor
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ABSTRACT: To provide evidence for an analgesic effect of antler pedicle compression or lidocaine 'ring block' by comparing changes in median and spectral edge frequencies and total electroencephalographic (EEG) power during the application of each technique followed by antler removal.
Twenty-nine 2-year-old red deer (Cervus elaphus) stags weighing 106-131 kg each were used in this study. Stags were carrying immature growing antler suitable for commercial harvest.
Anaesthesia was induced using propofol (8.25 +/- 1.28 mg kg(-1)) and ketamine (2.18 +/- 0.15 mg kg(-1)) and maintained with halothane in oxygen. End-tidal halothane (Fe'HAL), expired CO(2) tension (Pe'CO(2)), SpO(2), EEG, ECG, and direct arterial blood pressures were recorded continuously. Respiratory rate and somatic responses were recorded at specific time points. After stabilization of anaesthesia (Fe'HAL was approximately 0.8%) baseline data were recorded. Stags were randomly allocated to one of three treatment groups; control, local anaesthesia, or compression band. One antler was removed 4 minutes after the application of treatment. Electroencephalographic responses to application of treatment and antler removal were analysed using area under the curve (AUC) analysis. Mean AUC was compared between groups using anova, and when significant differences were found, groups were compared post hoc with two-tailed t-tests. Significance levels were set at p </= 0.05.
Median frequency (F(50)) was increased during antler removal in the control group and during both application and antler removal in the compression group. In the lidocaine group, F(50) was decreased during both application and antler removal. Spectral edge frequency (F(95)) was increased during the antler removal period in the control group and during both application and antler removal in the compression group. In the lidocaine group, F(95) was decreased in the application time period. Total EEG power (P(tot)) was decreased in the removal period in the control group. In the compression group, P(tot) was decreased in the removal period. In the lidocaine group, P(tot) was decreased in the application period. There were no significant differences in EEG variables between antler removal in the control group and application of compression (p = 0.19-0.96).
These data suggest that lidocaine 'ring block' of the antler pedicle provides adequate analgesia for velvet antler removal. The use of antler pedicle compression bands represents a noxious stimulus in its own right and is not as protective as lidocaine 'ring block' against the noxious stimulus of surgical antler removal.
Compression of the antler pedicle has been recommended as an alternative to lidocaine 'ring block' for velvet antler removal. The results of this study suggest that antler pedicle compression is noxious. In addition, antler pedicle compression offers less effective analgesia than lidocaine 'ring block'.
Veterinary Anaesthesia and Analgesia 03/2005; 32(2):61-71. · 0.94 Impact Factor
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ABSTRACT: To compare changes in heart rate and arterial pressures resulting from compression of the antler pedicle or lidocaine 'ring block' and during subsequent antler removal during minimal halothane anaesthesia.
Twenty-nine 2-year-old red deer (Cervus elaphus) stags, weighing 106-131 kg and carrying immature growing antler suitable for commercial harvest were studied.
Anaesthesia was induced using intravenous propofol (median dose 8.0 mg kg(-1), range 5.2-11.0) and ketamine (median dose 2.2 mg kg(-1), range 1.9-2.4) and maintained using halothane in oxygen. End-tidal halothane concentration (Fe'HAL) end-tidal CO(2) tension (Pe'CO(2)), SpO(2), EEG, ECG, and direct systolic (SAP) mean (MAP) and diastolic (DAP) arterial pressures were recorded continuously. Respiratory rate and somatic responses were recorded. Baseline data were recorded once anaesthesia (Fe'HAL approximately 0.8%) was stable. Stags were randomly allocated to control, lidocaine 'ring block' or compression band treatment groups. One antler was removed 4 minutes after treatment. Cardiovascular responses to the application of analgesia and antler removal were analysed using a general estimates equation for repeated measures or area under the curve (AUC) analysis. Mean AUC was compared between groups using anova, and when significant differences were found, groups were compared post hoc with two-tailed t-tests. Somatic response data were compared with Fisher's exact chi-square test. A value of p < 0.05 was considered significant.
Heart rate fell during observations in all groups with no significant differences between groups. Arterial pressures in the control and lidocaine groups during treatment and removal were not different from baseline values or from each other. Compression group pressures were significantly higher than baseline during both treatment and removal. Compression group DAP and MAP were significantly higher after antler removal than during treatment. In control and lidocaine groups, the AUC for SAP, DAP, and MAP over the combined baseline, treatment, and removal period did not differ. The compression group AUC for DAP and MAP were significantly greater over the experimental period than both the lidocaine group and control groups. Somatic responses occurred in one animal at lidocaine injection and three at compression application. Somatic responses occurred in eight control animals and two in the compression group at antler removal. More animals responded to antler removal in the control group than in the compression (p = 0.015) or lidocaine (p < 0.001) groups.
Compression of the antler pedicle appears to be noxious. Pedicular compression is a less effective analgesic technique for antler removal compared to 'ring blocks' with lidocaine.
This study suggests that lidocaine 'ring blocks' are the current technique of choice for antler removal in deer.
Veterinary Anaesthesia and Analgesia 03/2005; 32(2):72-82. · 0.94 Impact Factor
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ABSTRACT: To identify changes in the amplitude spectrum of the electroencephalogram (EEG) during a standardized surgical model of nociception in horses.
Thirteen entire male horses and ponies referred to Division of Clinical Veterinary Science, Bristol (n = 9) and Department of Clinical Veterinary Medicine (n = 4) for castration.
Following pre-anaesthetic medication with acepromazine, anaesthesia was induced with guaiphenesin and thiopental and maintained with halothane in oxygen. The EEG was recorded continuously using subcutaneous needle electrodes. Additional monitoring comprised ECG, arterial blood pressure, blood gas analysis, airway gases, and body temperature. All animals were castrated using a closed technique. The raw EEG was analysed after completion of each investigation and the EEG variables median frequency (F50), spectral edge frequency (SEF) 95% and total amplitude were derived from the spectra using standard techniques. The mean values of EEG variables recorded during a baseline time period (recorded before the start of surgery) and castration of each testicle were compared using analysis of variance for repeated measures.
Total amplitude (Atot) decreased and F50 increased during castration of each testicle compared to the baseline time period [(89.0 +/- 7.8% testicle 1, 87.0 +/- 7.8% testicle 2) and (110.0 +/- 15.0% testicle 1, 109.0 +/- 15.0% testicle 2), respectively]. Changes in SEF 95% were not significant.
De-synchronization was identified in the EEG during the nociceptive stimulus of castration. The results suggest that an increase in F50 may be a specific marker for nociception in the horse.
Studies investigating the efficacy of analgesic agents in horses are limited by difficulties in peri-operative pain assessment. This model, using EEG changes associated with nociceptive stimulation, can be used to investigate the anti-nociceptive efficacy of different anaesthetic agents in the horse.
Veterinary Anaesthesia and Analgesia 08/2003; 30(3):138-46. · 0.94 Impact Factor
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[show abstract]
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ABSTRACT: The study aim was to develop a model to generate cerebral evoked potentials (CEPs) by mechanical distention of the duodenum in rats. Twenty Sprague–Dawley rats were anaesthetized and the EEG recorded from the left and right somatosensory cortices (S1L, S1R). A balloon catheter was implanted into the duodenum. A pneumatic device, triggered by data acquisition software, inflated the balloon for 200 ms every 3 s to deliver a repeatable noxious stimulus. EEG was recorded for 100 ms before and 500 ms after onset of inflation and the response to 512 stimuli averaged to generate a CEP. Two CEPs were generated in each animal and data summed to calculate a single CEP for each channel.Data were excluded when the signal to noise ratio was <2, therefore data are presented from 11 animals. A repeatable CEP was identified in waveforms recorded from S1L. The mean (S.D.) CEP comprised a triphasic waveform (P1, N1, P2) with latencies of 246.0 (24.7), 289.3 (12.8) and 321.5 (13.2) ms, respectively. We are the first group to have generated and characterized a CEP following mechanical stimulation of the duodenum. This model can be applied to further elucidate the mechanisms leading to visceral pain perception.
Journal of Neuroscience Methods.
