Objective Propofol may cause adverse effects (e.g. apnoea, hypotension) at induction of anaesthesia. Co-induction of anaesthesia may reduce propofol requirements. The effect of fentanyl or midazolam on propofol dose requirements and cardiorespiratory parameters was studied.
Study design Randomized, controlled, blinded clinical study.
Animals Sixty-six client owned dogs (35 male, 31 female, ASA I-II, age 6–120 months, body mass 4.7–48.0 kg) were selected.
Methods Pre-medication with acepromazine (0.025 mg kg−1) and morphine (0.25 mg kg−1) was administered by intramuscular injection. After 30 minutes group fentanyl-propofol (FP) received fentanyl (2 μg kg−1), group midazolam-propofol (MP) midazolam (0.2 mg kg−1) injected over 30 seconds via a cephalic catheter and in a third group, control-propofol (CP), the IV catheter was flushed with an equivalent volume of heparinized saline. Anaesthesia was induced 2 minutes later, with propofol (4 mg kg−1minute−1) administered to effect. After endotracheal intubation anaesthesia was maintained with a standardized anaesthetic protocol. Pulse rate, respiratory rate (RR) and mean arterial pressure (MAP) were recorded before the co-induction agent, before induction, and 0, 2 and 5 minutes after intubation. Apnoea ≥30 seconds was recorded and treated. Sedation after pre-medication, activity after the co-induction agent, quality of anaesthetic induction and endotracheal intubation were scored.
Results Propofol dose requirement was significantly reduced in FP [2.90 mg kg−1(0.57)] compared to CP [3.51 mg kg−1 (0.74)] and MP [3.58 mg kg−1(0.49)]. Mean pulse rate was higher in MP than in CP or FP (p = 0.003). No statistically significant difference was found between groups in mean RR, MAP or incidence of apnoea. Activity score was significantly higher (i.e. more excited) (p = 0.0001), and quality of induction score was significantly poorer (p = 0.0001) in MP compared to CP or FP. Intubation score was similar in all groups.
Conclusions and clinical relevance Fentanyl decreased propofol requirement but did not significantly alter cardiovascular parameters. Midazolam did not reduce propofol requirements and caused excitement in some animals.