The medium effective concentration of remifentanil for blunting cardiovascular responses to new laryngeal masks insertion versus tracheal intubation under propofol sedation

Abstract

Objective To measure the medium effective concentration (EC50) of remifentanil for blunting cardiovascular response to placement of LMA-Fastrach, LMA-Proseal and tracheal intubation, and to compare the change of brain bispectral index (BIS) during these procedures. Methods Sixty-three patients (ASA I-II) scheduled for cholecystectomy under general anesthesia were enrolled. According to different options of intubation, all the patients were randomly allocated into three groups (n=21 each): group T by laryngoscope and tracheal intubation, group F by LMA-Fastrach and group P by LMA-Proseal.Initially, a target plasma concentration of 4 mg/L propofol was chosen, and was adjusted to maintain BIS between 45 and 55. Then, the effect-site concentration of remifentanil was started at designed concentration according to Minto's pharmacokinetic model. Five minutes later, 0.6 mg/kg (2 ED95) rocuronium was given, and intubation was performed 2 min after rocuronium administration. The pre- and post-induction mean arterial pressure (MAP), heart rate (HR) and BIS were compared among these groups. MAP and HR at 1 and 2 min pre-intubation and at 5 min post-intubation were also recorded to evaluate whether there was a cardiovascular response in these patients. Subsequently, the EC50 of remifentanil for blunting the cardiovascular response to 3 options of intubation was calculated using the Dixon-Mood up- and down- sequence. Results Compared with pre-induction, all the patients in 3 groups experienced significantly lower post-inductive MAP and HR [MAP of pre- and post-induction in T, F, P groups were (87.9±10.5) mm Hg vs (71.6±9.0) mm Hg, (91.8±8.8)mm Hg vs (73.5±9.9) mm Hg, (87.2±10.2) mm Hg vs (70.9±8.6) mm Hg, HR of pre- and post-induction in T, F, P groups were (78.8±11.6) min-1 vs (68.7±8.5) min-1,(74.8±10.3) min-1 vs (64.1±6.7) min-1, (76.7±8.2) min-1 vs (67.3±8.3) min-1,1 mm Hg=0.133 kPa, P 0.05). The EC50 of remifentail for blunting cardiovascular response to intubation was 4.47 μg/L for group T, 4.78 μg/L for group F and 2.05 μg/L for group P, respectively. Conclusion EC50 of remifentail for blunting cardiovascular responses to intubation as shown by Minto's model appears slightly higher in LMA-Fastrach than that in tracheal intubation, and the lowest is in LMA-Proseal intubation. Key words: Target-controlled infusion; Bispectral index; Propofol; Remifentanil; Medium effective concentration