R. E. Clutton

Post anaesthetic colic in horses: a preventable complication?

REASONS FOR PERFORMING STUDY There is little information on the prevalence of, and risk factors associated with, post anaesthetic colic (PAC) in horses undergoing nonabdominal operations. OBJECTIVES To undertake the first prospective study of prevalence of PAC and identify risk factors in its development in nonabdominal procedures. METHODS A multicentre prospective case-control study was conducted, on every horse undergoing anaesthesia for a nonabdominal procedure between April 2004 and June 2005. Colic cases were defined as any horse with recognised signs of abdominal pain within 72 h of general anaesthesia that could not be attributed to any concurrent disease. Five control horses per case were selected randomly from the study population at all hospitals. Multivariable logistic regression analysis was used to examine the relationship between predictor variables and the risk of developing PAC. RESULTS The estimated mean prevalence of PAC in the study population was 5.2% (95% CI, 2.8, 8.0). However, the prevalence of colic varied between each centre. The most commonly diagnosed cause of colic was impaction. Multivariable analyses showed that the centre involved and the type of surgery performed were associated with an increased risk of PAC. Preoperative food deprivation and the use of opioid drugs were confounding factors. CONCLUSIONS Prevalence of PAC varied significantly between the 4 hospitals studied; there may be hospital-related covariates that account for this. The type of surgery performed influenced the risk of PAC. POTENTIAL RELEVANCE Identifying the risk factors for PAC is a prerequisite for its prevention. This study indicates horses at increased risk of PAC that might benefit from a more critical evaluation of post anaesthetic gastrointestinal function and/or the provision of preventative measures. Further investigation is required to explain the variation in prevalence of PAC between centres.

Comparison of three injectable anaesthetic techniques in pigs

Forty-six near-adult pigs (mean age 10 months, mean weight 156 kg) were anaesthetised for laparoscopy. After intramuscular azaperone (1.0 mg/kg) and ketamine (2.5 mg/kg), 14 of the pigs received intravenous etomidate (200 μg/kg) and midazolam (100 μg/kg) and 17 were given ketamine (2 mg/kg) and midazolam (100 μg/kg). The other 15 pigs were anaesthetised with pentobarbitone (15 to 20 mg/kg) without pre-anaesthetic medication. The duration and adequacy of anaesthesia, recovery rate, and seven physiological variables (ECG, heart rate, indirect arterial blood pressure, respiratory rate, minute volume, mean end-tidal carbon dioxide concentration and percentage oxygen saturation of haemoglobin) were compared. Repeated injections were needed in 29 of the 46 cases. Pentobarbitone was the least satisfactory drug because although the haemodynamic variables were greater, it caused more respiratory depression and a higher overall complication rate than the other methods. Apnoea occurred in two pigs, and was fatal in one, and positive pressure ventilation with oxygen was needed in three others. Intubation conditions were poorer and the times to standing, walking and rooting were longer in the pigs anaesthetised with pentobarbitone.

Effect of muscle injection site on preanaesthetic sedation in dogs

The demeanour of 122 dogs was assessed, and a mixture of 0.025 mg/kg acepromazine and 03 mg/kg morphine was injected intramuscularly into one of four randomly assigned muscle sites (cervical epaxial, triceps brachii, middle gluteal and quadriceps femoris) and the dogs’ reactions to the injections were assessed. The development of sedation and the occurrence of side effects were assessed after 10, 20 and 30 minutes, and each dog’s reaction to venous catheterisation was scored. All the dogs became similarly sedated after 30 minutes. The degree of sedation and the incidence of side effects were independent of the injection site, but the dogs receiving intragluteal injections had lower sedation scores after 10 minutes. The dogs’ demeanour had no effect on their response to venous catheterisation. The dogs receiving an injection into the postural quadriceps and triceps muscles showed more marked reactions than those injected into the non-postural cervical epaxial and gluteal muscles.

Anaesthesia for lambs undergoing spinal surgery: a case series

Six 1-month-old lambs were anaesthetized for cervical spinal cord surgery. Anaesthesia was induced with intravenous midazolam (0.5 mg/kg) then halothane delivered by mask in an O2–N2O mixture. After endotracheal intubation, the lungs were ventilated mechanically and anaesthesia maintained with halothane and nitrous oxide. Buprenorphine and flunixin were given before and after surgery, and the wound margin was infiltrated with 0.5% bupivacaine solution. Neuromuscular block was produced with repeated injections of atracurium; neuromuscular transmission was restored with edrophonium. Lambs made a rapid recovery without obvious signs of discomfort, sedation, or weakness after operations lasting up to 156 min. Anaesthesia was induced in a seventh lamb using etomidate, which probably contributed to death during recovery from anaesthesia.

Spontaneous electroencephalographic changes in a castration model as an indicator of nociception: A comparison between donkeys and ponies

REASONS FOR PERFORMING STUDY Donkeys are believed to be less demonstrative of pain than ponies. Research into comparative sensory processing between these species is required to elucidate these behavioural differences. OBJECTIVES To compare changes in the electroencephalogram (EEG) recorded during castration between donkeys and ponies. STUDY DESIGN Prospective clinical study. METHODS Six ponies and 6 donkeys were castrated under halothane anaesthesia after acepromazine premedication and thiopental anaesthetic induction. Markers were inserted into the EEG recording at the time of skin incision (skin) and emasculation (emasc) for both testicles (T1 and T2) during a closed castration. Raw EEG data were analysed and the EEG variables median frequency (F50 ), total power (Ptot ) and spectral edge frequency (F95 ) derived using standard techniques. Baseline values of F50 , Ptot and F95 for each animal were used to calculate the percentage change from baseline at T1skin, T2skin, T1emasc and T2emasc. RESULTS Decreased F50 values relative to baseline were observed in 4 ponies and 2 donkeys across all castration time points. In the remaining animals, the F50 value increased compared with baseline. Both donkey and pony groups showed an overall decrease in Ptot values compared with baseline at T1skin, but the magnitude of the decrease was significantly less (P = 0.004) in ponies than in donkeys. Donkeys demonstrated an overall greater increase (P = 0.05) in F95 values at T1skin relative to baseline compared with ponies. CONCLUSIONS Electroencephalographic responses to the noxious stimulus of castration were noted in both donkeys and ponies. Donkeys demonstrated a greater change in Ptot in response to castration than ponies; thus, donkeys appear to demonstrate a cerebral cortical response to a noxious stimulus that is similar to or greater than that in ponies, suggesting that their subtle behavioural expression of pain is not due to a difference in cortical processing of noxious sensory stimuli.

A comparison of the neuromuscular and cardiovascular effects of vecuronium, atracurium and mivacurium in sheep

Neuromuscular and cardiovascular effects of vecuronium, atracurium and mivacurium were compared in 45 sheep. The onset and duration of neuromuscular block produced with loading doses of vecuronium (25 microg kg(-1)), atracurium (500 microg kg(-1)) and mivacurium (200 microg kg(-1)) and maintained with incremental doses (7, 170 and 70 microg kg(-1), respectively) were monitored using train-of-four stimulation of the n. facialis-m. levator nasolabialis unit. The electrocardiogram, heart rate and arterial blood pressure were recorded during onset of neuromuscular blockade. Mean loading dose onset times for atracurium (98 seconds) and mivacurium (86 seconds) were significantly shorter than vecuronium (203 seconds). Vecuronium produced significantly longer block (40 minutes) than atracurium (28 minutes) and mivacurium (15 minutes). There was no evidence of drug cumulation with atracurium or mivacurium. Cardiac dysrrhythmias were not observed in any group. Atracurium and mivacurium produced intermediate- and short-duration neuromuscular blockade, respectively. Vecuronium produced a prolonged effect after a slow onset.

A model describing the use of a bronchial blocking device and a sheathed bronchoscope for pulmonary aspiration studies in the Göttingen minipig

The administration of test substances into a single lung, or lung lobe, allows the remaining untreated lung to act as an experimental control and effectively halves the number of animals required in a given experiment. It reduces the likelihood of early fatal pulmonary failure when noxious substances are studied which may lessen the need for replacement animals. However, the ease of substance administration and the subsequent analysis of its effects, for example by bronchoalveolar lavage or bronchoscopy, depend critically on the size of the animal model. The advantages of using minipigs; ease of handling, reduced housing requirements, genetic homogeneity, etc. are reduced if their diminutive size makes lung studies difficult. This article describes the use of a bronchial blocking device and a sheathed bronchoscope which enabled sterile endobronchial substance administration in Göttingen minipigs, and allowed pulmonary aspiration studies to be conducted with each animal acting as its own control.

Reducing the oxygen concentration of gases delivered from anaesthetic machines unadapted for medical air.

High fractional concentrations of inspired oxygen (FiO2) delivered over prolonged periods produce characteristic histological changes in the lungs and airway of exposed animals. Modern medical anaesthetic machines are adapted to deliver medical air (FiO2=0.21) for the purpose of reducing FiO2; anaesthetic machines designed for the veterinary market have not been so adapted. Two inexpensive modifications that allow medical air to be added to the gas flow from veterinary anaesthetic machines are described. The advantages and disadvantages of each modification are discussed.

An Experimental Evaluation of a new Intraparenchymal Continuous Compliance Probe: Preliminary Studies

The Spiegelberg automated compliance device offers practical benefits over the standard manual injection techniques for assessing volume-pressure status. Currently, however, the system relies on the insertion of an intraventricular catheter. If automated continuous measurement of intraparenchymal compliance could be achieved, then this would be a further practical advance. Automated measurements of compliance using a prototype intraparenchymal probe were assessed in comparison with the current intraventricular probe in a sheep model of diffusely raised ICP. The results show poor correlation between intraventricular compliance (IVC) and intraparenchymal compliance (IPC) at low levels of cerebral perfusion pressure (CPP). The IPC response to decreasing CPP beyond probable levels of blood flow autoregulation suggest that IPC is more dependent on local tissue perfusion factors, rather than overall physical compliance. Further evaluation of compliance in the intraparenchymal compartment versus intraventricular compliance will be needed before adaptation of the automated system for clinical application.

Spontaneous electroencephalographic changes in a castration model as an indicator of nociception: A comparison between donkeys and ponies: Electroencephalographic response to nociception in donkeys and ponies

REASONS FOR PERFORMING STUDY Donkeys are believed to be less demonstrative of pain than ponies. Research into comparative sensory processing between these species is required to elucidate these behavioural differences. OBJECTIVES To compare changes in the electroencephalogram (EEG) recorded during castration between donkeys and ponies. STUDY DESIGN Prospective clinical study. METHODS Six ponies and 6 donkeys were castrated under halothane anaesthesia after acepromazine premedication and thiopental anaesthetic induction. Markers were inserted into the EEG recording at the time of skin incision (skin) and emasculation (emasc) for both testicles (T1 and T2) during a closed castration. Raw EEG data were analysed and the EEG variables median frequency (F50 ), total power (Ptot ) and spectral edge frequency (F95 ) derived using standard techniques. Baseline values of F50 , Ptot and F95 for each animal were used to calculate the percentage change from baseline at T1skin, T2skin, T1emasc and T2emasc. RESULTS Decreased F50 values relative to baseline were observed in 4 ponies and 2 donkeys across all castration time points. In the remaining animals, the F50 value increased compared with baseline. Both donkey and pony groups showed an overall decrease in Ptot values compared with baseline at T1skin, but the magnitude of the decrease was significantly less (P = 0.004) in ponies than in donkeys. Donkeys demonstrated an overall greater increase (P = 0.05) in F95 values at T1skin relative to baseline compared with ponies. CONCLUSIONS Electroencephalographic responses to the noxious stimulus of castration were noted in both donkeys and ponies. Donkeys demonstrated a greater change in Ptot in response to castration than ponies; thus, donkeys appear to demonstrate a cerebral cortical response to a noxious stimulus that is similar to or greater than that in ponies, suggesting that their subtle behavioural expression of pain is not due to a difference in cortical processing of noxious sensory stimuli.