Effective Target Plasma Concentration Of Remifentanil Required To Blunt Tracheal Intubation Response In 50% Of Children

Objective To determine the effective target plasma concentration of remifentanil required to blunt tracheal intubation response in 50% of children(Cp50 ) induced with sevoflurane at end-tidal 1MAC(minimum alveolar concentration).Methods ASA I or II patients aged 2~5 yrs undergoing elective surgical operation under general anesthesia were enrolled in this study. The patients were premedicated with intramuscular atropine 0.015mg·kg-1 and midazolam 0.1mg·kg-1. BP,HR,SpO2,and ECG were continuously monitored and recorded before intubation (baseline) and at 1and 2 min after intubation. Anesthesia was induced with 8% sevoflurane in 100% oxygen through a semi-closed anesthetic circuit. The speed of fresh gas flow was 3L·min-1. As soon as the patients failed to respond to verbal command and eyelash reflex disappeared, the concentration delivered was adjusted to obtain sevoflurane at end-tidal 1MAC and to keep it constant for 2 minutes. Then remifentanil was administered using target-controlled infusion with the Minto model. Target plasma concentration of remifentanil was selected for each patient according to an up-and-down method . The ratio of two consecutive target plasma concentration was 1.2. After 10 minutes, tracheal intubation was performed and accomplished within 30 seconds. Positive intubation response was defined as increase in MAP and/or HR≥15% of the baseline value within 2min after intubation. The experiment started from target plasma concentration of remifentanil 6μg·L-1. The first enrolled patient was calculated from the one before who had positive response for intubation. Patients were enrolled until six pairs positive-negative crossovers to obtain .Results The Cp50 of remifentanil was 3.6μg·L-1 .The 95% confidence interval was 3.1~4.0μg·L-1.Conclusion Remifentanil target plasma concentration at 3.6μg·L-1 together with sevoflurane at end-tidal 1 MAC can suppress cardiovascular responses to tracheal intubation in 50% of children.