Effects of midazolam before or after alfaxalone for co-induction of anaesthesia in healthy dogs

Objective To study the effect of alternating the order of midazolam and alfaxalone administration on the incidence of behavioural changes, alfaxalone induction dose and some cardiorespiratory variables in healthy dogs. Study design Prospective, randomized, controlled, clinical trial. Animals A total of 33 client-owned dogs undergoing elective procedures. Methods Following intramuscular acepromazine (0.02 mg kg(-1)) and morphine (0.4 mg kg(-1)) premedication, anaesthesia was induced intravenously (IV) with a co-induction of either midazolam (0.25 mg kg(-1)) prior to alfaxalone (0.5 mg kg(-1); group MA), or alfaxalone followed by midazolam at identical doses (group AM). The control group (CA) was administered normal saline IV prior to alfaxalone administration. Additional alfaxalone (0.25 mg kg(-1) increments) was administered as required in all groups until orotracheal intubation was possible. Changes in behaviour, quality of induction, ease of intubation and incidence of adverse events at induction were recorded. Heart rate (HR), respiratory rate (f(R)) and systolic arterial blood pressure (SAP) were measured before treatments (baseline values), 30 minutes after premedication and at 0, 2, 5 and 10 minutes postintubation. Results The incidence of excitement was higher in group MA compared with groups CA (p = 0.005) and AM (p = 0.013). The mean induction dose of alfaxalone was lower in group AM compared with group CA (p = 0.003). Quality of induction and ease of intubation were similar among groups. Mean HR values decreased after premedication and increased after alfaxalone administration in all groups. Mean SAP values were similar between groups. The number of animals that required manual ventilation was higher in the MA group. Conclusions and clinical relevance Despite a lower occurrence of adverse events at induction in group AM compared with group MA and a reduction of alfaxalone dose requirement in group AM compared with group CA, the use of an alfaxalonee midazolam co-induction does not seem to produce any cardiovascular or respiratory benefits in healthy dogs.