Sight hounds, including Greyhounds, are known to clear some anaesthetics at a slower rate than other dog breeds and, therefore, a decrease in the dose rate may be necessary to maintain safety. This two period cross-over study was designed to determine the cardiorespiratory safety and anaesthetic effects of the upper end recommended dose rate of Alfaxan®-CD RTU when combined with or without acepromazine and morphine in Greyhound dogs. Eight, intact Greyhound dogs were used in the study (4M/4F) ranging from 15 to 30 months of age and 24 to 34.5 kg body weight. Dogs were blocked by weight and gender and randomized to treatment group and study day. Acepromazine (0.03 mg/kg) and morphine (0.3 mg/kg) were administered intramuscularly 20 min before Alfaxan®-CD RTU administration at 2 mg/kg body weight intravenously over 60 seconds. On the day of study, data were collected immediately before premedication, 10 minutes after premedication, immediately after anaesthetic induction, during anaesthesia and at recovery. Pulse rate (min^-1), respiratory rate (min^-1), haemoglobin oxygen saturation (SpO₂%), end tidal CO₂ (mm Hg), body temperature (°C) and mucous membrane colour were recorded. Anaesthetic times calculated for each dog included time to onset of anaesthesia (intubation), duration of anaesthesia, time to head lift, time to sternal recumbency and time to standing without aid. Quality of induction anaesthesia, anaesthesia and recovery were also scored using an ordinal system of 4, 3, 2 and 1 (i.e., excellent, good, fair and poor respectively). Dogs were intubated upon anaesthetic induction and breathed room air during anaesthesia.

Alfaxan®-CD-RTU produced good to excellent anaesthesia in both unpremedicated and premedicated Greyhound dogs at 2 mg/kg intravenously over a period of 60 seconds. The longest period of induction apnoea (one dog) was 60 seconds. Transition from consciousness to unconsciousness (i.e., lateral recumbency) was uneventful and without incident. Cardiovascular, respiratory and body temperature data are presented in Table 1:

Table 1. Average (±SD) physiological parameters in Greyhounds (± premedication) anaesthetised with Alfaxan-CD RTU.

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Durations of anaesthesia* are presented in Table 2:

Table 2. Average (± SD) quality and time parameters in Greyhounds (± premedication) anaesthetised with Alfaxan-CD RTU.

* Time zero was the point at which Alfaxan-CD RTU administration was initiated in the patient.

Anaesthetic quality scores (i.e., frequencies) observed during anaesthesia are presented in Table 3:

Table 3. Quality scores for Greyhounds (± premedication) anaesthetized with Alfaxan-CD RTU.

Anaesthesia produced by Alfaxan®-CD-RTU in Greyhound dogs with and without premedication was typified by excellent muscle relaxation. Cardiovascular and respiratory data were within normal ranges for clinical anaesthesia in dogs. As expected, durations of anaesthesia were longer for premedicated dogs than unpremedicated dogs. The duration of anaesthesia in unpremedicated Greyhound dogs (7.13 ± 1.70 min) observed in this study was similar to Beagle dogs (6.4 ± 2.9 min) observed in a previous study¹. Quality scores for anaesthesia were similar for the two treatment groups except during recovery where the premedicated group had better quality scores.

In conclusion, Alfaxan®-CD RTU when administered to Greyhound dogs at 2 mg/kg IV over 60 seconds can be used safely to produce good to excellent short term anaesthesia. The duration of anaesthesia observed is similar to that of other dogs. Premedication of Greyhound dogs with acepromazine and morphine provides better recovery from anaesthesia than without premedication.

References

1.  Ferre PJ, Pasloske K, Whittem T, et al. Plasma pharmacokinetics of alfaxalone in dogs after an intravenous bolus of Alfaxan-CD RTU. Veterinary Anaesthesia and Analgesia 2006;33:229-236.