Effect of remifentanil on requirements for propofol administered by use of a target-controlled infusion system for maintaining anesthesia in dogs

Abstract

Objective - To evaluate the effect of remifentanil administered by use of a constant rate infusion on the predicted plasma concentration (Cp predicted) of propofol required to prevent awareness in 50% of anesthetized dogs (Cp50predicted). Animals - 6 healthy dogs. Procedures - Each dog received 2 treatments (1-week interval): induction and maintenance of anesthesia with propofol alone and induction of anesthesia with propofol and maintenance of anesthesia by use of propofol and a constant rate infusion of remifentanil (0.3 μg/kg/min). To induce anesthesia, propofol was administered by use of a target-controlled infusion system to achieve Cp predicted of 6.0 μg/mL. Propofol Cppredicted was adjusted in 0.5 μg/mL increments or decrements; the motor response to a supramaximal electrical nociceptive stimulus was assessed after each change to determine Cp50predicted (mean of the highest Cppredicted at which gross purposeful movement was detected in response to stimulation and the lowest Cppredicted at which such movement was not detected). Results - Mean ± SD duration of anesthesia for dogs receiving propofol (148 ± 35 minutes) and dogs receiving propofol-remifentanil treatment (141 ± 28 minutes) did not differ. Overall mean propofol Cp predicted for induction of anesthesia was 6.0 ± 0.5 μg/mL. For maintenance of anesthesia, propofol Cp50predicted was significantly reduced following addition of remifentanil to the protocol (2.0 ± 0.5 μg/mL vs 0.9 ± 0.4 μg/mL; 55% decrease). Conclusions and Clinical Relevance - In nonpremedicated dogs, propofol Cp50 predicted of 6.0 μg/mL may be recommended for induction of anesthesia. Propofol requirements for maintaining target-controlled infusion system-based anesthesia were reduced via infusion of remifentanil at a rate of 0.3 μg/kg/min.