Effect-site concentration of remifentanil blunting cardiovascular responses to the insertion of the laryngeal mask airway

Objective To determine the effect-site concentration of remifentanil blunting cardiovascular responses to the insertion of the laryngeal mask airway in the situation of BIS at 45-55.Methods Thirty-one patients undergoing selective gynaecological laparoscopy were enrolled in this study.Anesthesia was induced with midazolam-propofol-vecuronium-remifentanil in sequence.When obtaining a stable BIS value ranging between 45 and 55 after midazolam-propofol infusion,vecuronium was infused,and then remifentanil infusion was started.Remifentanil was administered through a target plasma concentration determined by a modified Dixon's up-and-down method.After achieveing the balance between the plasma and effect-site concentation of remifentanil,an experienced anaesthetist inserted the laryngeal mask airway.We ended the study after 8 crossovers(successive accept and refuse appear)had been obtained.Results Twenty-nine patients were enrolled in this study,and the mean EC50 of remifentanil was 2.0 ng/ml(95% confidence interval 1.8-2.2 ng/ml)for laryngeal mask airway insertion.Conclusion This study showed that effect-site concentration of remifentanil of 2.0 ng/ml is effective in blunting cardiovascular responses to insert the laryngeal mask airway in 50% of patients respectively during a stable BIS value ranging between 45 and 55.