Co-induction of anaesthesia with alfaxalone and midazolam in dogs: a randomized, blinded clinical trial

Abstract

Objective: To qualitatively assess the co-induction of anaesthesia with midazolam and alfaxalone and to determine cardiovascular or respiratory alterations compared with alfaxalone alone.

Study design: A randomized, blinded, clinical trial.

Animals: A total of 29 American Society of Anesthesiologists grade I or II, client-owned dogs undergoing elective orthopaedic or soft tissue surgery.

Methods: All dogs received 0.02 mg kg^-1 acepromazine and 0.3 mg kg^-1 methadone intramuscularly 30 minutes prior to anaesthesia. Measurements of heart rate (HR), respiratory frequency and blood pressure (BP) were assessed pre-induction and at 0, 2 and 5 minutes post-induction. Anaesthesia was induced with 0.5 mg kg^-1 alfaxalone followed by either 0.4 mg kg^-1 midazolam intravenously (group M) or an equal volume of saline (group S). Conditions were assessed for intubation and further boluses of 0.25 mg kg^-1 alfaxalone were given as required. Response to co-induction, ease of intubation and quality of induction were scored, and total dose of alfaxalone required for intubation was recorded. Repeated measures one-way analysis of variance with post hoc Tukey's test was used to assess within group changes over time and Student t tests were used to compare between groups. Incidence of apnoea was assessed using a Fisher's exact test. Data are shown as mean ± standard deviation.

Results: Group M included 14 dogs and group S 15 dogs. There was a significant difference in the total dose of alfaxalone required for intubation, 0.65 ± 0.20 mg kg^-1 group M and 0.94 ± 0.26 mg kg^-1 group S (p = 0.002). Apnoea occurred significantly more frequently in group M (p = 0.007). There were no clinically significant differences in HR or BP at the measured time points between groups.

Conclusions and clinical relevance: Co-induction with midazolam had significant alfaxalone-sparing effects with no clinically detectable cardiovascular changes. Apnoea is common after co-induction.

Keywords: alfaxalone; apnoea; co-induction; dogs; midazolam.