Optimal Propofol Infusion Rate in Dogs

In the Literature

Walters K, Lehnus K, Liu N-C, Bigby SE. Determining an optimum propofol infusion rate for induction of anaesthesia in healthy dogs: a randomized clinical trial. Vet Anaesth Analg. 2022;49(3):243-250. doi:10.1016/j.vaa.2021.07.006

The Research …

Propofol (premedicated dogs, 1-4 mg/kg; nonpremedicated dogs, 6.5 mg/kg; IV over10-40 seconds and titrated to effect) is commonly administered for smooth, rapid induction of general anesthesia.¹ Benefits include rapid onset, short duration of action, quick redistribution, and short elimination half-life.² Adverse effects are dose dependent, with postinduction apnea and hypotension being most common.^3,4 Slow administration rate may decrease incidence of apnea.

This randomized, blinded clinical trial sought to determine the optimal propofol infusion rate for rapid tracheal intubation and reduction of postinduction apnea in healthy dogs. Dogs were randomly assigned into 5 groups. All dogs were premedicated with methadone (0.5 mg/kg IM) and dexmedetomidine (5 μg/kg IM). Thirty minutes after premedication, dogs were preoxygenated via facemask for 5 minutes. Each group was administered a different propofol infusion rate (0.5, 1, 2, 3, or 4 mg/kg/minute IV) for induction via syringe pump; infusions were discontinued once a dog was ready for intubation. After intubation, dogs were monitored until spontaneous breathing occurred. Time to intubation and duration of apnea were recorded. Cardiopulmonary variables (eg, heart and respiratory rates, oxygen saturation, blood pressure) were measured.

Propofol infusion rate had significant effects on both time to intubation and duration of apnea. Of the 60 dogs that completed the study, those that received propofol at 0.5 mg/kg/minute or 1 mg/kg/minute had a significantly shorter duration of apnea. None of the 60 dogs desaturated during the study. Between these 2 groups, intubation time was shorter in dogs that received propofol at 1 mg/kg/minute. Effect on blood pressure was not significantly different among groups.

Based on results of this study, the optimal rate of propofol infusion for induction of general anesthesia is 1 mg/kg/minute. Slow titration is recommended so propofol concentrations can equilibrate between the blood and the brain to achieve loss of consciousness with minimal adverse effects. Faster infusion rates lead to higher plasma concentration that exceeds the minimum dose to achieve unconsciousness, increasing the likelihood of apnea and hypotension.

This study only evaluated healthy dogs premedicated with methadone and dexmedetomidine. The cardiovascular effect of dexmedetomidine-induced vasoconstriction may have helped minimize the hypotensive effect of propofol. The effect of a priming bolus to help reduce total propofol induction dose was not evaluated.

… The Takeaways

Key pearls to put into practice:

• Propofol should be administered slowly IV and titrated to effect during induction; premedicated dogs require a lower dose.

• Slow administration allows for a time delay between drug administration and loss of consciousness, as propofol concentrations need to equilibrate between the blood and brain.

• Rapid administration can cause postinduction apnea, which can result in desaturation if patients are not preoxygenated prior to induction.