Midazolam, as a co-induction agent, has propofol sparing effects but also decreases systolic blood pressure in healthy dogs

Objective: To evaluate the effects of the co-administration of midazolam on the dose requirement for propofol anesthesia induction, heart rate (HR), systolic arterial pressure (SAP) and the incidence of excitement. Study design: Prospective, randomized, controlled and blinded clinical study, with owner consent. Animals: Seventeen healthy, client owned dogs weighing 28 ± 18 kg and aged 4.9 ± 3.9 years old. Methods: Dogs were sedated with acepromazine 0.025 mg kg^-1 and morphine 0.25 mg kg^-1 intramuscularly (IM), 30 minutes prior to induction of anesthesia. Patients were randomly allocated to receive midazolam (MP; 0.2 mg kg^-1) or sterile normal saline (CP; 0.04 mL kg^-1) intravenously (IV) over 15 seconds. Propofol was administered IV immediately following test drug and delivered at 3 mg kg^-1 minute^-1 until intubation was possible. Scoring of pre-induction sedation, ease of intubation, quality of induction, and presence or absence of excitement following co-induction agent, was recorded. HR, SAP and respiratory rate (f_R) were obtained immediately prior to, immediately following, and 5 minutes following induction of anesthesia. Results: There were no significant differences between groups with regard to weight, age, gender, or sedation. Excitement occurred in 5/9 dogs following midazolam administration, with none noted in the control group. The dose of propofol administered to the midazolam group was significantly less than in the control group. Differences in HR were not significant between groups. SAP was significantly lower in the midazolam group compared with baseline values 5 minutes after its administration. However, values remained clinically acceptable. Conclusions and clinical relevance: The co-administration of midazolam with propofol decreased the total dose of propofol needed for induction of anesthesia in sedated healthy dogs, caused some excitement and a clinically unimportant decrease in SAP.