Evaluation of a non-rebreathing circuit for small animal anaesthesia

Several new multi-purpose non-rebreathing anaesthetic systems have been developed for human anaesthesia. This study evaluated a New Zealand designed non-rebreathing circuit, the Palmerston Valve, in anaesthetised spontaneously breathing dogs and compared it to the widely used Lack coaxial circuit. Arterial blood gas measurements 60 minutes after induction demonstrated comparable slight increases in PaCO₂ in nearly all dogs maintained on the Palmerston Valve and Lack coaxial circuit with halothane and oxygen mixtures, and a fresh gas flow rate of 70 ml/kg/min.

Results suggest the Palmerston Valve is at least as efficient as the Lack coaxial circuit, while offering in the same unit the potential for economical controlled ventilation.     

Clinical evaluation of the Lack coaxial breathing circuit in small animal anaesthesia

The performance of the Lack co-axial breathing circuit was evaluated in 25 anaesthetized dogs breathing spontaneously. Fresh gas flows were adjusted until rebreathing started to occur as judged by capnography. Thus a critical fresh gas flow rate was determined for small (10–15 kg) and larger (15 + kg) dogs. These were 130.5 ± 31.2 and 95.9 ± 13-1 ml/kg/min respectively. In a further twenty dogs weighing over 15 kg a fresh gas flow rate of 120 ml/kg/min was used and was found to be sufficient to prevent rebreathing in all cases. In 11 dogs a direct comparison was made between the Lack and the Magill circuits with fresh gas flows of 120 ml/kg/min and it was found by capnography that while there was minimal or no rebreathing with the Lack system there was substantial rebreathing with the Magill.     

Survey on small animal anaesthesia

OBJECTIVE: To ascertain anaesthetic practices currently for dogs and cats in Australia. METHODS: A questionnaire was distributed to 4,800 veterinarians throughout Australia, seeking data on numbers of dogs and cats anaesthetised per week; drug preferences for anaesthetic premedication, induction and maintenance; use of tracheal intubation, supplemental nitrous oxide and anaesthetic antagonists; and types of vaporisers, breathing systems and anaesthetic monitoring devices used or available. Additional questions concerned proportions of different animal types seen in the practice, and the respondent's university and year of graduation. RESULTS: The response rate was 19%; 95% of respondents graduated from Australian universities, about half since 1985. Most responses (79%) came from mainly small animal practices. On average 16 dogs and 12 cats were anaesthetised each week. Premedication was used more often in dogs than cats, with acepromazine and atropine most favoured in both species. For anaesthetic induction, thiopentone was most preferred in dogs and alphaxalone/alphadolone in cats. Inhaled agents, especially halothane, were preferred for maintenance in both species. Most respondents usually employed tracheal intubation when using inhalational anaesthetic maintenance, but intubation rates were lower during injectable anaesthetic maintenance and a minority of respondents provided supplemental O2. Nitrous oxide was administered regularly by 13% of respondents. The agents most frequently used to speed recovery from anaesthesia were doxapram and yohimbine. The most widely used vaporisers were the Fluotec Mark III and the Stephens machine. Most (95%) respondents used a rebreathing circuit for large dogs and a non-rebreathing system was used for small dogs by 68% of respondents. Most respondents (93%) indicated some form of aid was available to monitor general anaesthesia: the three most mentioned were an apnoea alarm, oesophageal stethoscope and electrocardiogram. CONCLUSION: Diverse approaches were evident, but there appeared to be less variation in anaesthetising dogs: premedication was more frequent and less varied in type, while thiobarbituates dominated for induction and inhalants for maintenance. Injectable maintenance techniques had substantial use in cats, but little in dogs. Evident disparity between vaporisers available and circuits used suggested either confusion in terminology or incorrect use of some vaporisers in-circuit. While most respondents used monitoring equipment or a dedicated observer to invigilate anaesthesia, the common reliance on apnoea alarms is of concern, because of unproven reliability and accuracy.     

Perioperative mortality in small animal anaesthesia

Anaesthetic complications have been studied intermittently in small animal practice. Current estimates suggest that approximately 0.1–0.2% of healthy and 0.5–2% of sick dogs and cats die of an anaesthetic-related death. This is substantially greater than the risk of mortality reported in human anaesthesia. Recent work has identified the post-operative period as the highest risk period and has documented a number of risk factors for mortality. Knowledge of factors associated with anaesthetic-related death and high risk peri-operative periods could aid patient management and reduce complications.     

The EMO system in small animal anaesthesia

The EMO System was used to administer ether/air anaesthesia to dogs undergoing clinical surgical procedures. Anaesthesia with spontaneous breathing gave rise to normal oxygen tensions in arterial blood, a slight acidosis and a decrease in arterial carbon dioxide tension. When used with relaxant drugs and intermittent positive pressure ventilation of the lungs it was found that to maintain normal oxygen tensions in the arterial blood it was necessary to hyperventilate to low arterial carbon dioxide tensions. Ether/air anaesthesia with the EMO System was found to meet modern criteria for acceptability in general practice where the veterinary surgeon may be assisted in the operating theatre by a nurse or may be entirely alone.     

Recommended techniques in small animal anaesthesia: An update

A protocol for anaesthesia of healthy small animals (dogs and cats) is described with the emphasis on good technique. The anaesthetic period is considered in stages from pre-operative evaluation through to recovery.     

A survey of anaesthesia in small animal practice: AVA/BSAVA report

Over 150 veterinary surgeons from 53 small animal practices collaborated in a prospective survey of anaesthetic accidents and emergencies by recording all anaesthetics administered and detailing the problems they encountered. From these records it is estimated that 1 in 679 of the healthy dogs and cats died primarily as a result of anaesthesia; many of these deaths apparently occurred at a time when the animal was not under close observation. Anaesthetics involving the use of xylazine seemed to result in an exceptionally high mortality rate. Complications following endotracheal intubation appeared to be associated with several deaths in cats. The death rate in cats and dogs with pathological but not immediately life-threatening conditions was estimated to be 1 in 31. There was no evidence to suggest that some breeds (with the possible exception of the Pekingese) were more likely than others to die under anaesthesia.     

Evaluation of a modified exogenous creatinine clearance as a suitable renal function test for the small animal practice

A suitable method in the routine veterinary practice for the quantitative determination of the glomerular filtration rate (GFR) in dogs and cats has not been available until to date. Therefore, we modified the known plasma clearance model (=P-CL). The resulting P-CLterminal was assessed concerning its diagnostic value. P-CL of exogenous creatinine (P-CLcrea) and of inulin were determined in dogs (n=12, Beagle, 6 months of age) and cats (n=11, Domestic Short Hair, 14 months of age). The marker substances were administered as a bolus injection. In fasted dogs, P-CLcrea was 84.3 +/- 14.85 ml/min/m2 after a creatinine dose of 2.4 g/m2. An electrolyte infusion during the clearance determination did not alter the resulting values (p>0.05). In fasted cats, P-CLcrea was 54.7 +/- 5.8 ml/min/m2 (creatinine dose 2.0 g/m2). The inulin clearance, determined at the same time, was 104.5 +/- 19.81 ml/min/m2. Feeding the cats just before and during the test increased P-CL of both markers significantly (p<0.05). In order to adapt the clearance method for diagnostic assessment of GFR in the small animal practice, we aimed at minimizing the number of required blood samples (3 instead of 7 or more) and introduced the modified exogenous creatinine clearance (P-CLterminal). These values determined were 108.4 +/- 20.81 ml/min/m2 in fasted dogs and 66.3 +/- 11.81 ml/min/m2 in fasted cats. An electrolyte infusion (dogs) and feeding (cats) had the same effect on P-CLterminal values as described above for P-CL. In conclusion,the modified exogenous creatinine clearance is a suitable renal function test for the early diagnosis of renal disease in dogs and cats presented in small animal practices.     

动物麻醉监测的研究进展

麻醉监测是应用人的感观、电子、声、光学等技术及时发现动物机体各种生理指标的变化,将感官监测与仪器监测相结合,更好的判断麻醉深度,是保障麻醉安全和提高麻醉质量的诊断手段.麻醉深度过浅会使动物感到疼痛,在手术中产生未预料到的活动,对手术不利;麻醉过深则对动物生命安全造成威胁.通过麻醉监测,才能了解动物麻醉的深浅程度、麻醉动物的生理功能是否在它的耐受范围之内,这样才能保证诊疗和外科手术的顺利进行,保证动物的安全及康复痊愈.     

Assessment of the variation in American Society of Anaesthesiologists Physical Status Classification assignment in small animal anaesthesia

ObjectiveTo evaluate the interobserver variability in the assignment of the American Society of Anesthesiologists Physical Status Classification (ASA-PSC) to compromised small animal patients amongst a group of veterinary anaesthetists.Study designAnonymous internet survey.AnimalsHypothetical case presentations.MethodsSixteen hypothetical small animal cases with differing degrees of physiological or patho-physiological compromise were presented as part of an internet survey. Respondents were asked to assign a single ASA-PSC to each case and also to answer a number of demographic questions. ASA-PSC scores were considered separately and then grouped as scores of I–II and III–V. Agreement was analysed using the modified kappa statistic for multiple observers. Data were then sorted into various demographic groups for further analysis.ResultsThere were 144 respondents of which 60 (～42%) were anaesthesia diplomates, 24 (～17%) were post-residency (nondiploma holders), 24 (～17%) were current anaesthesia residents, 21 (～15%) were general practitioners, 12 (～8%) were veterinary nurses or technicians, and 3 (～2%) were interns. Although there was a majority agreement (>50% in a single category) in 15 of the 16 cases, ASA-PSC were spread over at least three ASA-PS classifications for every case. Overall agreement was considered only fair (κ = 0.24, mean ± SD agreement 46 ± 7%). When comparing grouped data (ASA-PSC I–II versus III-V) overall agreement remained fair (κ = 0.36, mean ± SD agreement 69 ± 19%). There was no difference in ASA-PSC assignment between any of the demographic groups investigated.Conclusions and clinical relevanceThis study suggests major discrepancies can occur between observers given identical information when using the ASA-PSC to categorise health status in compromised small animal patients. The significant potential for interobserver variability in classification allocation should be borne in mind when the ASA-PSC is used for clinical, scientific and statistical purposes.