A comparison in dogs of medetomidine, with or without MK-467, and the combination acepromazine-butorphanol as premedication prior to anaesthesia induced by propofol and maintained with isoflurane

Abstract

Objective: To compare the haemodynamic effects of three premedicant regimens during propofol-induced isoflurane anaesthesia.

Study design: Prospective, randomized cross-over study.

Animals: Eight healthy purpose-bred beagles aged 4 years and weighing mean 13.6 ± SD 1.9 kg.

Methods: The dogs were instrumented whilst under isoflurane anaesthesia prior to each experiment, then allowed to recover for 60 minutes. Each dog was treated with three different premedications given intravenously (IV): medetomidine 10 μg kg⁻¹ (MED), medetomidine 10 μg kg⁻¹ with MK-467 250 μg kg⁻¹ (MMK), or acepromazine 0.01 mg kg⁻¹ with butorphanol 0.3 mg kg⁻¹ (AB). Anaesthesia was induced 20 minutes later with propofol and maintained with isoflurane in oxygen for 60 minutes. Heart rate (HR), cardiac output, arterial blood pressures (ABP), central venous pressure (CVP), respiratory rate, inspired oxygen fraction, rectal temperature (RT) and bispectral index (BIS) were measured and arterial and venous blood gases analyzed. Cardiac index (CI), systemic vascular resistance index (SVRI), oxygen delivery index (DO₂ I), systemic oxygen consumption index (VO₂ I) and oxygen extraction (EO₂) were calculated. Times to extubation, righting, sternal recumbency and walking were recorded. The differences between treatment groups were evaluated with repeated measures analysis of covariance.

Results: HR, CI, DO₂ I and BIS were significantly lower with MED than with MMK. ABP, CVP, SVRI, EO₂, RT and arterial lactate were significantly higher with MED than with MMK and AB. HR and ABP were significantly higher with MMK than with AB. However, CVP, CI, SVRI, DO₂ I, VO₂ I, EO₂, T, BIS and blood lactate did not differ significantly between MMK and AB. The times to extubation, righting, sternal recumbency and walking were significantly shorter with MMK than with MED and AB.

Conclusions and clinical relevance: MK-467 attenuates certain cardiovascular effects of medetomidine in dogs anaesthetized with isoflurane. The cardiovascular effects of MMK are very similar to those of AB.

Keywords: MK-467; acepromazine; dog; general anaesthesia; haemodynamics; medetomidine.