Effects of propofol on isoflurane minimum alveolar concentration and cardiovascular function in mechanically ventilated goats

Abstract

OBJECTIVE: To evaluate the effects of propofol, on isoflurane minimum alveolar concentration (MAC) and cardiovascular function in mechanically ventilated goats. STUDY DESIGN: Prospective, randomized, crossover experimental study. ANIMALS: Six goats, three does and three wethers. METHODS: General anaesthesia was induced with isoflurane in oxygen. Following endotracheal intubation, anaesthesia was maintained with isoflurane in oxygen. Intermittent positive pressure ventilation was applied. Baseline isoflurane MAC was determined, the noxious stimulus used being clamping a claw. The goats then received, on separate occasions, three propofol treatments intravenously: bolus of 0.5 mg kg-1 followed by a constant rate infusion (CRI) of 0.05 mg kg-1 minute-1 (Treatment LPROP); bolus of 1.0 mg kg-1 followed by a CRI of 0.1 mg kg-1 minute-1 (Treatment MPROP), bolus of 2.0 mg kg-1 followed by a CRI of 0.2 mg kg-1 minute-1 (Treatment HPROP). Isoflurane MAC was re-determined following propofol treatments. Plasma propofol concentrations at the time of MAC confirmation were measured. Cardiopulmonary parameters were monitored throughout the anaesthetic period. Quality of recovery was scored. The Friedman test was used to test for differences between isoflurane MACs. Medians of repeatedly measured cardiovascular parameters were tested for differences between and within treatments using repeated ANOVA by ranks. (P < 0.05 for statistical significance). RESULTS: Isoflurane MAC [median (interquartile range)] was 1.37 (1.36-1.37) vol%. Propofol CRI significantly reduced the isoflurane MAC, to 1.15 (1.08-1.15), 0.90 (0.87-0.93) and 0.55 (0.49-0.58) vol% following LPROP, MPROP and HPROP treatment, respectively. Increasing plasma propofol concentrations strongly correlated (Spearman rank correlation) with decrease in MAC (Rho = 0.91). Cardiovascular function was not affected significantly by propofol treatment. Quality of recovery was satisfactory. CONCLUSIONS AND CLINICAL RELEVANCE: In goats, propofol reduces isoflurane MAC in a dose-dependent manner with minimal cardiovascular effects.