Hatim Alibhai

Cardiopulmonary effects of combinations of medetomidine hydrochloride and atropine sulphate in dogs

Medetomidine and xylazine are alpha 2 adrenoceptor agonists which are used as sedatives and premedicants in small animals. However, bradycardia is a side effect and the use of atropine sulphate has been recommended to counteract it. This study investigated the effects of combining medetomidine (40 μg/kg) and atropine (30 μg/kg) on the cardiopulmonary function of six dogs. Medetomidine administered alone caused severe bradycardia, but hypertension was mild and transient. Medetomidine and atropine administered together caused an initial bradycardia, but within 15 minutes there was tachycardia accompanied by a mean arterial blood pressure of 210 mm Hg. When atropine was administered 30 minutes before medetomidine, tachycardia and hypertension were observed within five minutes of the medetomidine injection. Thus, although atropine will counteract medetomidineinduced bradycardia, its use results in prolonged and severe hypertension, in association with the tachycardia. Although atropine may be life-saving when bradycardia is profound, its indiscriminate use in combination with alpha 2 adrenoceptor agonists may be disadvantageous.

Cardiopulmonary effects of desflurane in the dog during spontaneous and artificial ventilation.

The cardiopulmonary effects of desflurane at end tidal concentrations of 10.3, 12.9 and 15.5 per cent during either spontaneous or artificial ventilation were studied in five beagle dogs. Desflurane anaesthesia resulted in tachycardia and a decrease in arterial blood pressure which were not significantly related to the end tidal desflurane concentrations or the mode of ventilation. At an end tidal desflurane concentration of 15.5 per cent there was a significant increase in central venous and pulmonary arterial wedge pressures and, with artificial ventilation, a reduction in cardiac output and stroke volume when compared with similar measurements at an end tidal desflurane concentration of 10.3 per cent. When allowed to breathe spontaneously, the dogs panted at times when they were lightly anaesthetised, but their respiration was depressed to a varying extent at the highest end tidal desflurane concentration. The induction of anaesthesia with desflurane was smooth, and the quality of anaesthesia during maintenance was excellent. There was one episode of a transient tachyarrhythmia associated with the measurement of cardiac output, but no other side effects were observed.

Clinical efficacy and cardiorespiratory effects of alfaxalone, or diazepam/fentanyl for induction of anaesthesia in dogs that are a poor anaesthetic risk

OBJECTIVE To evaluate the clinical efficacy and cardiorespiratory effects of alfaxalone as an anaesthetic induction agent in dogs with moderate to severe systemic disease. STUDY DESIGN Randomized prospective clinical study. ANIMALS Forty dogs of physical status ASA III-V referred for various surgical procedures. METHODS Dogs were pre-medicated with intramuscular methadone (0.2 mg kg(-1) ) and allocated randomly to one of two treatment groups for induction of anaesthesia: alfaxalone (ALF) 1-2 mg kg(-1) administered intravenously (IV) over 60 seconds or fentanyl 5 μg kg(-1) with diazepam 0.2 mg kg(-1) ± propofol 1-2 mg kg(-1) (FDP) IV to allow endotracheal intubation. Anaesthesia was maintained with isoflurane in oxygen and fentanyl infusion following both treatments. All dogs were mechanically ventilated to maintain normocapnia. Systolic blood pressure (SAP) was measured by Doppler ultrasound before and immediately after anaesthetic induction, but before isoflurane administration. Parameters recorded every 5 minutes throughout subsequent anaesthesia were heart and respiratory rates, end-tidal partial pressure of carbon dioxide and isoflurane, oxygen saturation of haemoglobin and invasive systolic, diastolic and mean arterial blood pressure. Quality of anaesthetic induction and recovery were recorded. Continuous variables were assessed for normality and analyzed with the Mann Whitney U test. Repeated measures were log transformed and analyzed with repeated measures anova (p<0.05). RESULTS Treatment groups were similar for continuous and categorical data. Anaesthetic induction quality was good following both treatments. Pre-induction and post-induction systolic blood pressure did not differ between treatments and there was no significant change after induction. The parameters measured throughout the subsequent anaesthetic procedures did not differ between treatments. Quality of recovery was very, quite or moderately smooth. CONCLUSIONS AND CLINICAL RELEVANCE Induction of anaesthesia with alfaxalone resulted in similar cardiorespiratory effects when compared to the fentanyl-diazepam-propofol combination and is a clinically acceptable induction agent in sick dogs.

CARDIOPULMONARY EFFECTS OF DESFLURANE IN PONIES, AFTER INDUCTION OF ANAESTHESIA WITH XYLAZINE AND KETAMINE

Cardiopulmonary parameters were measured in 12 ponies (small horses) before anaesthesia and, following induction with xylazine and ketamine, during maintenance of anaesthesia with desflurane. In six of the ponies (group A) anaesthesia was maintained for three hours with desflurane at an endtidal concentration of 7.4 per cent. In the other six ponies (group B), anaesthesia was maintained in the same way for one hour and then the effects of end-tidal desflurane concentrations of 7.4 per cent and 9.6 per cent with and without artificial ventilation were investigated. In group A ponies the arterial blood pressure and the systemic vascular resistance index (sviu) decreased significantly during the first 45 minutes of anaesthesia but recovered with time. The cardiac index and heart rates were unchanged throughout the measurement period but arterial carbon dioxide tensions increased significantly. In group B ponies, with either mode of ventilation, increasing desflurane concentration resulted in decreases in arterial blood pressure, cardiac index and mixed venous oxygen tension, although the changes were not always statistically significant. There were marked individual differences in the cardiovascular responses to the high desflurane concentrations, the minimum mean arterial blood pressure ranging from 35 to 62 mm Hg, and the cardiac index from 23 to 50 ml/kg/min. The study concludes that during maintenance of anaesthesia with end tidal concentrations of desflurane of 7.4 per cent, cardiac index is well maintained and the initial fall in arterial blood pressures results from a fall in svRi. However, increasing the concentration of desflurane causes a fall in blood pressure due to cardiac depression.

Evaluation of the quality of the recovery after administration of propofol or alfaxalone for induction of anaesthesia in dogs anaesthetized for magnetic resonance imaging.

OBJECTIVE To compare the quality of the recovery when propofol or alfaxalone were administered for the induction of anaesthesia in dogs undergoing neurological diagnostic procedures. EXPERIMENTAL DESIGN Prospective, randomized clinical trial. ANIMALS Forty two client-owned dogs, 21 females and 21 males, weighing between 5.7 and 55 kg. METHODS Each dog was sedated with methadone (0.2 mg kg(-1) intramuscularly or 0.1 mg kg(-1) intravenously). Sedation was scored after 30 minutes. Anaesthesia was induced either with propofol or alfaxalone, administered to enable orotracheal intubation, after which anaesthesia was maintained with sevoflurane in oxygen. At the end of the procedure, the animals recovered in the clinical area. Quality of recovery was scored (early recovery) using simple descriptive and visual analogue scales (SDS and VAS). When sternal recumbency was achieved, dogs were moved to the recovery room and recovery was scored again (late recovery). Quantitative data were assessed with the Mann-Whitney U test, Kruskal-Wallis test, Spearmans rank correlation and Bland Altman plots as appropriate, whilst categorical data were analysed with the Chi square test and weighted kappa. RESULTS Sex, behaviour and duration of anaesthesia did not influence recovery scores. Dogs had poorer late recovery scores in the alfaxalone group compared to the propofol group (SDS, p = 0.014; VAS, p = 0.017). Degree of sedation after premedication influenced assessed SDS scores during early (p = 0.038) and late recovery (p = 0.008) (dogs more heavily sedated recovered better). However by VAS scores, sedation did not statistically influence early recovery (p = 0.299) but did affect late recovery (p = 0.013). Rescue sedation (medetomidine) was required only in two dogs in the alfaxalone group. CONCLUSIONS Induction of anaesthesia with alfaxalone was associated with poorer recovery than with propofol in animals receiving premedication with methadone. CLINICAL RELEVANCE Greater attention to the recovery environment may be advisable when using alfaxalone for induction of anaesthesia where minimal premedication has been used. Further sedation in recovery may be required.

Comparison of quality of recovery from anaesthesia in cats induced with propofol or alfaxalone

OBJECTIVE To assess the quality and length of recovery from anaesthesia induced with either propofol or alfaxalone and maintained with isoflurane, in cats undergoing short procedures in private veterinary practice. STUDY DESIGN Prospective, blinded, randomized study. ANIMALS Ninety-three healthy mixed breed cats. METHODS After premedication with intramuscular acepromazine (0.05 mg kg(-1)) and buprenorphine (0.01 mg kg(-1)), cats were randomly allocated to receive either propofol (Group P) or alfaxalone (Group A) for induction of anaesthesia. Following endotracheal intubation, anaesthesia was maintained with isoflurane vaporized in oxygen. The quality of induction, physiological parameters throughout anaesthesia and the duration of both surgery and anaesthesia were recorded. The level of ambient noise, recovery times, number of attempts to stand, reaction of the cat to touch 15 minutes after extubation, and other relevant characteristics of the recovery period were noted and a video recording of the recovery was made. The videos were assessed by a second, blinded anaesthetist, using simple descriptive and visual analogue scales. RESULTS No statistically significant differences between groups with respect to preoperative data, premedication, surgery, anaesthesia and recovery times and scores were observed. There was a statistically significant difference in the number of patients paddling and trembling on recovery in Group A (p = 0.032) even though there was no statistically significant difference in the level of ambient noise in the recovery ward or in the overall quality of recovery. CONCLUSIONS Both propofol and alfaxalone provide good recovery characteristics in premedicated cats undergoing short procedures in clinical settings. Alfaxalone induction was associated with more episodes of paddling and trembling during recovery. CLINICAL RELEVANCE Both agents would appear appropriate for induction of anaesthesia in cats for short procedures.

Extracorporeal liver assist device to exchange albumin and remove endotoxin in acute liver failure: Results of a pivotal pre-clinical study

Background & Aims In acute liver failure, severity of liver injury and clinical progression of disease are in part consequent upon activation of the innate immune system. Endotoxaemia contributes to innate immune system activation and the detoxifying function of albumin, critical to recovery from liver injury, is irreversibly destroyed in acute liver failure. University College London-Liver Dialysis Device is a novel artificial extracorporeal liver assist device, which is used with albumin infusion, to achieve removal and replacement of dysfunctional albumin and reduction in endotoxaemia. We aimed to test the effect of this device on survival in a pig model of acetaminophen-induced acute liver failure. Methods Pigs were randomised to three groups: Acetaminophen plus University College London-Liver Dialysis Device (n = 9); Acetaminophen plus Control Device (n = 7); and Control plus Control Device (n = 4). Device treatment was initiated two h after onset of irreversible acute liver failure. Results The Liver Dialysis Device resulted in 67% reduced risk of death in acetaminophen-induced acute liver failure compared to Control Device (hazard ratio = 0.33, p = 0.0439). This was associated with 27% decrease in circulating irreversibly oxidised human non-mercaptalbumin-2 throughout treatment (p = 0.046); 54% reduction in overall severity of endotoxaemia (p = 0.024); delay in development of vasoplegia and acute lung injury; and delay in systemic activation of the TLR4 signalling pathway. Liver Dialysis Device-associated adverse clinical effects were not seen. Conclusions The survival benefit and lack of adverse effects would support clinical trials of University College London-Liver Dialysis Device in acute liver failure patients.

A reproducible, clinically relevant, intensively managed, pig model of acute liver failure for testing of therapies aimed to prolong survival

A clinically relevant, translational large animal model of acute liver failure (ALF) is required for testing of novel therapies to prolong survival in acute liver failure, to permit spontaneous liver recovery or to act as a bridge to transplantation.

The risk of passive regurgitation during general anaesthesia in a population of referred dogs in the UK.

OBJECTIVE To evaluate the risk of passive regurgitation during anaesthesia, and to identify major factors associated with this in dogs attending the Queen Mother Hospital for Animals (QMHA), the Royal Veterinary College. STUDY DESIGN A case-control study nested within the cohort of dogs undergoing anaesthesia with inhalation agents. ANIMAL POPULATION All dogs undergoing general anaesthesia at the referral hospital between October 2006 and September 2008 (4271 cases). METHODS All dogs anaesthetized at the QMHA during the study period were included. Regurgitating cases were defined as dogs for which reflux material was observed at the external nares or in the mouth, either during anaesthesia or before return to normal consciousness immediately after general anaesthesia. The risk of regurgitation was estimated and risk factors for regurgitation were evaluated with multivariable logistic regression (p < 0.05). RESULTS The overall risk of regurgitation was 0.96% (41 cases out of 4271 anaesthetics, 95% confidence interval [95% CI] 0.67-1.25%). Exclusion of animals where pre-existing disease was considered a contributing factor to regurgitation (n = 14) resulted in a risk of passive regurgitation of 0.63% (27 cases of 4257 anaesthetics, 95% CI 0.40-0.87%). In the multivariable logistic regression model, procedure and patient weight were significantly associated with regurgitation. Dogs undergoing orthopaedic surgery were 26.7 times more likely to regurgitate compared to dogs undergoing only diagnostic procedures. Dogs weighing more than 40 kg were approximately five times more likely to regurgitate than those weighing <20 kg. CONCLUSIONS AND CLINICAL RELEVANCE This study highlights the rare but important occurrence of perioperative regurgitation and identifies that dogs undergoing orthopaedic procedures, and those weighing more than 40 kg, are particularly at risk. Further work is required to evaluate the reasons for these observations.

The effects of ephedrine on intramuscular blood flow and other cardiopulmonary parameters in halothane‐anesthetized ponies

OBJECTIVE To evaluate the effect of ephedrine on intramuscular blood flow and hemodynamic parameters during equine anesthesia. STUDY DESIGN Prospective experimental study. ANIMALS Six healthy adult Welsh Mountain ponies (five males, one female, mean weight: 267 kg, range: 213-347 kg). METHODS Halothane-anesthetized ponies received an IV bolus of ephedrine (0.1 mg kg-1), followed 30 minutes later by a second IV ephedrine injection (0.2 mg kg-1). Changes in intramuscular blood flows (IMBF) in upper and lower triceps brachii were measured by laser Doppler flowmetry. Cardiopulmonary measurements were made at intervals for 30 minutes following each injection. Results were compared with values from a control group, similarly anesthetized but given saline in an earlier study. RESULTS Ephedrine at either dose increased heart rate, arterial blood pressure (AP), cardiac index (CI) and intramuscular blood flow (IMBF), the effects on these parameters being significant and long-lasting following the higher dose. Systemic vascular resistance remained unchanged, and was significantly lower than in the control saline group. PaO2 decreased significantly immediately following the first injection of ephedrine, then remained unchanged for the remainder of the experiment. PaCO2 increased slowly throughout the anesthetic period. One pony developed supraventricular premature complexes following the second injection. No other side effects were seen. CONCLUSION Ephedrine at dose rates of 0.2 mg kg-1 IV consistently increased in CI, AP, and IMBF in both forelimbs. CLINICAL RELEVANCE Ephedrine may be of use to improve AP, CI and IMBF during halothane anesthesia, although the occurrence of an arrhythmia in one pony is of concern.