Postinduction apnoea in dogs premedicated with acepromazine or dexmedetomidine and anaesthetized with alfaxalone or propofol.

Objective: To compare incidence and duration of postinduction apnoea in dogs after premedication with methadone and acepromazine (MA) or methadone and dexmedetomidine (MD) followed by induction with propofol (P) or alfaxalone (A).

Study Design: Prospective, randomized clinical trial.

Animals: A total of 32 American Society of Anesthesiologists class I dogs (15 females, 17 males), aged between 4 months and 4 years, weighing between 3 and 46 kg.

Methods: Dogs were randomly allocated to be administered MA+P, MA+A, MD+P or MD+A (methadone 0.5 mg kg and acepromazine 0.05 mg kg or dexmedetomidine 5 μg kg). Induction agents were administered intravenously via syringe driver (P at 4 mg kg minute or A at 2 mg kg minute) until successful endotracheal intubation and the endotracheal tube connected to a circle system with oxygen flow at 2 L minute. Oxygen saturation of haemoglobin (SpO), end tidal partial pressure of carbon dioxide and respiratory rate were monitored continuously. If apnoea (≥ 30 seconds without breathing) occurred, the duration until first spontaneous breath was measured. If SpO decreased below 90% the experiment was stopped and manual ventilation initiated. Data were analysed with general linear models with significance set at p ≤ 0.05.

Results: There was no statistical difference in the incidence (11 of 16 dogs in A groups and 12 of 16 dogs in P groups), or mean ± standard deviation duration (A groups 125 ± 113 seconds, P groups 119 ± 109 seconds) of apnoea. The SpO of one dog in the MD+P group decreased below 90% during the apnoeic period.

Conclusions And Clinical Relevance: Propofol and alfaxalone both cause postinduction apnoea and the incidence and duration of apnoea is not influenced by the use of acepromazine or dexmedetomidine in premedication. Monitoring of respiration is recommended when using these premedication and induction agent combinations.