Determining an optimum propofol infusion rate for induction of anaesthesia in healthy dogs: a randomized clinical trial.

OBJECTIVE

To determine an optimum infusion rate of propofol that permitted rapid tracheal intubation while minimizing the duration of postinduction apnoea.

STUDY

DESIGN

Prospective, randomized, blinded clinical trial.

ANIMALS: A total of 60 client-owned dogs presented for elective neutering and radiography.

METHODS

Dogs were randomly allocated to one of five groups (groups A-E) to have propofol at an infusion rate of 0.5, 1, 2, 3, or 4 mg kg-1 minute-1, respectively, following intramuscular premedication with methadone 0.5 mg kg-1 and dexmedetomidine 5 μg kg-1. Propofol administration was stopped when adequate conditions for tracheal intubation were identified. Time to tracheal intubation and duration of apnoea were recorded. If oxygen haemoglobin saturation decreased to < 90%, manual ventilation was initiated. A one-way analysis of covariance was conducted to compare the effect of propofol infusion rate on duration of apnoea and intubation time whilst controlling for covariates, followed by post hoc tests. The significance level was set at p < 0.05.

RESULTS

Propofol infusion rate had a significant effect on duration of apnoea (p = 0.004) and intubation time (p < 0.001) after controlling for bodyweight and sedation scores, respectively. The adjusted means (± standard error) of duration of apnoea were significantly shorter in groups A and B (49 ± 39 and 67 ± 37 seconds, respectively) than in groups C, D and E (207 ± 34, 192 ± 36 and 196 ± 34 seconds, respectively). Group B (115 ± 10 seconds) had a significantly shorter intubation time than group A (201 ± 10 seconds, p < 0.001).

CONCLUSIONS AND CLINICAL RELEVANCE: An infusion rate of 1.0 mg kg-1 minute-1 (group B) appears to offer the optimal compromise between speed of induction and duration of postinduction apnoea.