Effects of midazolam on isoflurane minimum alveolar concentration in goats

Abstract

The effects of midazolam on the minimum alveolar concentration (MAC) of isoflurane in mechanically ventilated goats were evaluated. Six healthy goats (3 does and 3 wethers) were used in a randomized crossover design. General anaesthesia was induced with isoflurane. Endotracheal intubation was performed after which anaesthesia was maintained with isoflurane. Baseline isoflurane MAC was determined. The goats then received, on separate occasions, one of three midazolam treatments intravenously: bolus dose of 0.1 mg/kg followed by a maintenance dose of 0.1 mg/kg/h (Treatment LMID), bolus dose of 0.3 mg/kg followed by a maintenance dose of 0.3 mg/kg/h (Treatment MMID), bolus dose of 0.9 mg/kg followed by a maintenance dose of 0.9 mg/kg/h (Treatment HMID) intravenously. Isoflurane MAC was then re-determined for each midazolam treatment. The baseline [median (inter-quartile range)] isoflurane MAC in goats was 1.40 (1.38–1.41)%. Baseline isoflurane MAC was statistically significantly reduced (P < 0.05) following Treatment LMID, Treatment MMID and Treatment HMID by 16.8%, 35.1% and 54.7%, respectively. Quality of recovery from anaesthesia was good following all midazolam treatments. Midazolam, administered by constant rate infusion, significantly reduces isoflurane MAC in goats.