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.
