The effect of midazolam co-induction on cardiorespiratory variables, myoclonus and etomidate dose requirements in healthy cats

Objective: To evaluate dose requirements of etomidate for endotracheal intubation, with or without midazolam co-induction, and to describe induction quality and associated cardiorespiratory variables in healthy cats. Study design: Randomized prospective experimental study. Animals: A group of 24 adult neutered cats (17 females, seven males). Methods: Cats were premedicated with intramuscular butorphanol (0.4 mg kg^–1) and alfaxalone (2 mg kg^–1), and anesthesia was induced with etomidate following midazolam (0.3 mg kg^–1) or physiologic saline (0.06 mL kg^–1) intravenously. Heart rate, respiratory rate (f_R) and arterial blood pressure were measured following premedication, at co-induction, after etomidate administration, and after orotracheal intubation and compared using repeated-measures ANOVA. Pre- and post-etomidate blood samples were assessed for the presence of hemolysis. Etomidate dose requirements and prevalence of myoclonus were compared with Wilcoxon signed ranks test and Fisher's test. Values of p < 0.05 were considered significant. Results: Mean ± standard deviation etomidate doses required for orotracheal intubation were 0.84 ± 0.26 and 1.39 ± 0.33 mg kg^–1 for midazolam and saline co-induction, respectively (p = 0.001). The presence of myoclonus at sedated baseline, co-induction and etomidate was 6/12, 8/12 and 9/12 in the saline group, respectively, and 10/12, 2/12 and 0/12 in the midazolam group. The prevalence of myoclonus was lower in the midazolam group after co-induction and etomidate injection (p = 0.036 and p < 0.001, respectively). Cardiorespiratory variables did not differ between groups at any time point. Compared with baseline, f_R decreased in both groups after etomidate injection and intubation. Hemolysis was observed in all post-etomidate plasma samples. Conclusions and clinical relevance: Etomidate, with or without midazolam co-induction, provides acceptable cardiovascular function in premedicated healthy cats. Midazolam reduces etomidate requirements for orotracheal intubation and improves induction quality in cats premedicated with intramuscular butorphanol–alfaxalone.