A comparison of cardiopulmonary effects and anaesthetic requirements of two dexmedetomidine continuous rate infusions in alfaxalone-anaesthetized Greyhounds.

OBJECTIVE: To determine the effects of two dexmedetomidine continuous rate infusions on the minimum infusion rate of alfaxalone for total intravenous anaesthesia (TIVA), and subsequent haemodynamic and recovery effects in Greyhounds undergoing laparoscopic ovariohysterectomy. STUDY DESIGN: Prospective, randomized and blinded clinical study. ANIMALS: Twenty-four female Greyhounds. METHODS: Dogs were premedicated with dexmedetomidine 3 µg kg-1 and methadone 0.3 mg kg-1 intramuscularly. Anaesthesia was induced with IV alfaxalone to effect and maintained with a TIVA mixture of alfaxalone in combination with two different doses of dexmedetomidine (0.5 µg kg-1 hour-1 or 1 µg kg-1 hour-1; groups DEX0.5 and DEX1, respectively). The alfaxalone starting dose rate was 0.07 mg kg-1 minute-1 and was adjusted (± 0.02 mg kg-1 minute-1) every 5 minutes to maintain a suitable depth of anaesthesia. A rescue alfaxalone bolus (0.5 mg kg-1 IV) was administered if dogs moved or swallowed. The number of rescue boluses was recorded. Heart rate, arterial blood pressure and arterial blood gas were monitored. Qualities of sedation, induction and recovery were scored. Differences between groups were tested for statistical significance using a Student's t test or Mann-Whitney U test as appropriate. RESULTS: There were no differences between groups in sedation, induction and recovery quality, the median (range) induction dose of alfaxalone [DEX0.5: 2.2 (1.9-2.5) mg kg-1; DEX1: 1.8 (1.2-2.9) mg kg-1], total dose of alfaxalone rescue boluses [DEX0.5: 21.0 (12.5-38.8) mg; DEX1: 22.5 (15.5-30.6) mg] or rate of alfaxalone (DEX0.5: 0.12±0.04 mg kg-1 minute-1; DEX1: 0.12±0.03 mg kg-1 minute-1). CONCLUSIONS AND CLINICAL RELEVANCE: Co-administration of dexmedetomidine 1 µg kg-1 hour-1 failed to reduce the dose rate of alfaxalone compared with dexmedetomidine 0.5 µg kg-1 hour-1 in Greyhounds undergoing laparoscopic ovariohysterectomy. The authors recommend an alfaxalone starting dose rate of 0.1 mg kg-1 minute-1. Recovery quality was good in the majority of dogs.