Determination of the minimum infusion rate of propofol required to prevent purposeful movement of the extremities in response to a standardized noxious stimulus in goats

Abstract

Objective: To determine the minimum infusion rate (MIR) of propofol required to prevent purposeful movement in response to a standardized stimulus in goats. Study design: Prospective, experimental study. Animals: Eight healthy goats (four does, four wethers). Methods: Anaesthesia was induced with 4 mg kg−1 propofol intravenously (IV). A continuous IV infusion of propofol at 0.6 mg kg−1 minute−1 was initiated immediately to maintain anaesthesia. Following endotracheal intubation, goats breathed spontaneously via a circle breathing system delivering supplementary oxygen. The initial propofol infusion rate was maintained for 30 minutes before responses to noxious stimulation provided by clamping the proximal part of the claw with a Vulsellum forceps for 60 seconds were tested. In the presence or absence of purposeful movements of the extremities, the infusion rate was increased or reduced by 0.1 mg kg−1 minute−1 and held constant for 30 minutes before claw clamping was repeated. The propofol MIR for each goat was calculated as the mean of the infusion rates that allowed and abolished movement. Basic cardiopulmonary parameters were monitored, recorded and tested for statistical significance using Wilcoxon's signed rank test with Bonferroni adjustment for multiple testing. The quality of recovery from anaesthesia was assessed and scored. Results: The median MIR of propofol was 0.45 mg kg−1 minute−1 (range: 0.45–0.55 mg kg−1 minute−1). Induction and recovery were free of adverse behaviour. No statistically significant cardiopulmonary changes in comparison with baseline were observed, but clinically relevant hypoxaemia at 2 minutes after induction of anaesthesia was consistently observed. Chewing during anaesthesia was observed in three goats. Median times to extubation and standing were 3 minutes (range: 2–6 minutes) and 10 minutes (range: 7–21 minutes), respectively. Conclusions and clinical relevance: Propofol induction and maintenance of general anaesthesia minimally compromise cardiopulmonary function when oxygen is supplemented in goats.