Effect of fentanyl on the induction dose and minimum infusion rate of propofol preventing movement in dogs.

OBJECTIVE: To determine the effect of fentanyl on the induction dose of propofol and minimum infusion rate required to prevent movement in response to noxious stimulation (MIRNM ) in dogs.

STUDY DESIGN: Crossover experimental design.

ANIMALS: Six healthy, adult intact male Beagle dogs, mean±standard deviation 12.6±0.4 kg.

METHODS: Dogs were administered 0.9% saline (treatment P), fentanyl (5 μg kg-1 ) (treatment PLDF) or fentanyl (10 μg kg-1 ) (treatment PHDF) intravenously over 5 minutes. Five minutes later, anesthesia was induced with propofol (2 mg kg-1 , followed by 1 mg kg-1 every 15 seconds to achieve intubation) and maintained for 90 minutes by constant rate infusions (CRIs) of propofol alone or with fentanyl: P, propofol (0.5 mg kg-1  minute-1 ); PLDF, propofol (0.35 mg kg-1  minute-1 ) and fentanyl (0.1 μg kg-1  minute-1 ); PHDF, propofol (0.3 mg kg-1  minute-1 ) and fentanyl (0.2 μg kg-1  minute-1 ). Propofol CRI was increased or decreased based on the response to stimulation (50 V, 50 Hz, 10 mA), with 20 minutes between adjustments. Data were analyzed using a mixed-model anova and presented as mean±standard error.

RESULTS: ropofol induction doses were 6.16±0.31, 3.67±0.21 and 3.33±0.42 mg kg-1 for P, PLDF and PHDF, respectively. Doses for PLDF and PHDF were significantly decreased from P (p<0.05) but not different between treatments. Propofol MIRNM was 0.60±0.04, 0.29±0.02 and 0.22±0.02 mg kg-1  minute-1 for P, PLDF and PHDF, respectively. MIRNM in PLDF and PHDF was significantly decreased from P. MIRNM in PLDF and PHDF were not different, but their respective percent decreases of 51±3 and 63±2% differed (p=0.035).

CONCLUSIONS AND CLINICAL RELEVANCE: Fentanyl, at the doses studied, caused statistically significant and clinically important decreases in the propofol induction dose and MIRNM .