Continuous infusion of propofol in dogs premedicated with methotrimeprazine

Objective: To evaluate the cardiopulmonary and clinical effects of three different infusion rates of propofol in dogs premedicated with methotrimeprazine.

Study design: Randomized experimental trial.

Animals: Ten healthy adult mixed-breed male and female dogs, weighing from 14 to 20 kg.

Methods: Dogs were premedicated with methotrimeprazine [1 mg kg^-1 intravenously (IV)] followed by induction of anesthesia with 4.5 mg kg^-1 of propofol IV and maintenance with propofol for 60 minutes as follows: T1, 0.2 mg kg^-1 minute^-1; T2, 0.3 mg kg^-1minute^-1; and T3, 0.4 mg kg^-1minute^-1. Heart rate (HR), respiratory rate (RR), mean arterial pressure (MAP), end-tidal CO₂ (P_ETCO₂), arterial hemoglobin O₂ saturation, arterial blood gases, and pedal and cutaneous reflexes were measured before and 5, 10, 20, 30, 45 and 60 minutes after the beginning of the propofol infusion. Statistical analysis was performed using an anova.

Results: Heart rate increased during anesthesia in all cases and arterial blood pressure decreased only in dogs in the T3 category. Respiratory depression was proportional to the infusion rate of propofol. Muscle relaxation was satisfactory, but analgesia was inadequate in the three treatments.

Conclusions: The infusion of 0.2-0.4 mg kg^-1 minute^-1 of propofol produced a dose-dependent respiratory depression. The presence of a pedal withdrawal reflex and marked cardiovascular responses to this noxious stimulus suggests that anesthesia may not be of sufficient depth for surgery to be carried out.

Clinical relevance: Although several studies have been performed using propofol in animals, few studies have investigated the cardiopulmonary and analgesic effects with different doses. The determination of an adequate propofol infusion rate is necessary for the routine use of this intravenous anesthetic for the maintenance of anesthesia during major surgical procedures in dogs.