The dose-response relationship of remifentanil and propofol given by TCI for induction of anesthesia

Objective To compare the effects of target-controlled infusion (TCI) of remifentanil (R) in various doses in combination of TCI propofol (P) on hemodynamic response to tracheal intubation. Methods Fifty ASA Ⅰ - Ⅱ patients (18 male, 32 female) aged 65 yr undergoing elective surgery under general anesthesia were enrolled in this study. The patients were unpremedicated. Anesthesia was induced with remifentanil and propofol both given by TCI simultaneously. The patients were randomized to receive remifentanil at a fixed target plasma concentration of 0, 2, 4, 6 or 8 ng · ml-1 (group R0, R2, R4, R6, R8) . TCI propofol was started at a target plasma concentration of 3 μg · ml-1 . If the patients were still conscious in 5 min, target propofol concentration was increased by 1 μg·ml every 2 min until loss of consciousness (LOC, no response to voice command and loss of eyelash reflex). Trachea was then intubated following intravenous rocuronium . Intubation response was recorded (systolic blood pressure was 15 mm Hg higher than baseline (before intubation) within 2 min after intubation or HR 100 bpm) . The TCI system comprised Graseby 3500 infusion pump controlled by computer program Rugloop which included Marsh and Minto pharmacokinetic parameters. Results Induction time (from start of TCI R + P to LOC) was significantly longer in group RO and R2 than that in group R4, R6 and R8 ( P 0.05) . Plasma and effect-site concentrations of propofol at LOC were significantly higher in group RO and R2 than in group R4, R6 and R8 ( P 0.05) . MAP increased significantly for 2 min after intubation in group R2 and R4 but only for 1 min in group R6 and R8 ( P 0.05) . Conclusion Remifentanil potentiates propofol when given by TCI simultaneously for induction of anesthesia. The target plasma propofol concentration of 3 μg · ml-1 in the presence of plasma remifentanil concentration of 6 ng · ml-1 can effectively attenuate the intubation response.