Effects of fentanyl on isoflurane minimum alveolar concentration and cardiovascular function in mechanicallly ventilated goats

Abstract

Effects of fentanyl on minimum alveolar concentration (MAC) of isoflurane and cardiovascular function in mechanically-ventilated goats were evaluated using six healthy goats (3 does and 3 wethers). Following induction of general anaesthesia with isoflurane, endotracheal intubation was performed and anaesthesia maintained with isoflurane. Baseline isoflurane MAC in response to clamping a claw with a Vulsellum forceps was determined. Immediately after baseline isoflurane MAC determination, the goats then received, on separate occasions, one of three fentanyl treatments intravenously: bolus of 0.005 mg/kg followed by constant rate infusion (CRI) of 0.005 mg/kg/hour (Treatment LFENT), bolus of 0.015 mg/kg followed by CRI of 0.015 mg/kg/hour (Treatment MFENT), bolus of 0.03 mg/kg followed by CRI of 0.03 mg/kg/hour (Treatment HFENT). Isoflurane MAC was re-determined during fentanyl CRI treatments. Cardiopulmonary parameters were monitored. Quality of recovery was scored. A four-week washout period was allowed between treatments. The observed baseline isoflurane MAC was 1.32 (1.29-1.36)%. Isoflurane MAC decreased to 0.98 (0.92-1.01)%, 0.75 (0.69-0.79)% and 0.58 (0.51- 0.65)% following LFENT, MFENT and HFENT respectively. Cardiovascular function was not adversely affected. Quality of recovery from general anaesthesia was good, although exaggerated tail-wagging was observed on some goats following MFENT and HFENT. Fentanyl reduces isoflurane MAC in a dosedependent manner with minimal adverse cardiovascular effects in healthy, mechanically-ventilated goats.