Effect of rate of administration of propofol or alfaxalone on induction dose requirements and occurrence of apnea in dogs.

Objective To evaluate the effect of rate of administration of propofol or alfaxalone on induction dose requirements and incidence of postinduction apnea (PIA) in dogs following premedication with methadone and dexmedetomidine. Study design Prospective, randomized clinical trial. Animals Thirty-two healthy American Society of Anesthesiologists class I client-owned dogs (seven females, 25 males), aged between 5 and 54 months, weighing between 2.0 and 48.2 kg. Methods Dogs were premedicated intramuscularly with 0.5 mg kg(-1) methadone and 5 mg kg(-1) dexmedetomidine. Thirty minutes after premedication, dogs were preoxygenated for 5 minutes before the induction agent was administered intravenously via a syringe driver until orotracheal intubation was achieved. Dogs were randomized to receive alfaxalone 0.5 mg kg(-1) minute(-1) (ASlow), alfaxalone 2 mg kg(-1) minute(-1) (A-Fast), propofol 1 mg kg(-1) minute(-1) (P-Slow), or propofol 4 mg kg(-1) minute(-1) (P-Fast). Oxygen saturation of hemoglobin (SpO(2)), end-tidal carbon dioxide and respiratory rate were monitored. If PIA (>= 30 seconds without a breath) occurred, the time to the first spontaneous breath was measured. If SpO(2) decreased below 90%, the experiment was stopped and manual ventilation initiated. Results The mean +/- standard deviation induction doses of alfaxalone and propofol were lower in the A-Slow [A-Slow 0.9 +/- 0.3 mg kg(-1), A-Fast 2.2 +/- 0.5 mg kg(-1) (p = 0.001)] and P-Slow [P-Slow 1.8 +/- 0.6 mg kg(-1), P-Fast 4.1 +/- 0.7 mg kg(-1) (p = 0.001)] groups, respectively. The incidence of PIA was 25% for the A-Slow and P-Slow groups and 100% for the A-Fast and P-Fast groups (p = 0.007). Conclusions and clinical relevance Both propofol and alfaxalone following methadone and dexmedetomidine premedication caused PIA. Induction dose requirement and incidence of PIA were affected by the rate of administration of both drugs. When possible, propofol and alfaxalone doses should be reduced and administered slowly to reduce PIA.