Additive contribution of nitrous oxide to sevoflurane minimum alveolar concentration for tracheal intubation in children

Background: To study the interaction between nitrous oxide and sevoflurane during trachea intubation, thf authors determined the minimum alveolar conc entration of sevoflurane for tracheal intubation (MAC(TI)) with and without nitrous oxide in children. Methods: Seventy-two children aged 1-7 yr were assigned randomly to receive one of three end-tidal concentrations of nitrous oxide and one of four end -tidal concentrations of sevoflurane: 0% nitrous oxide with 2.0, 2.5, 3.0, or 3.5% sevoflurane; 33% nitrous oxide with 1.5, 2.0, 2.5, or 3.0% sevoflur ane; or 66% nitrous oxide with 1.0, 1.5, 2.0, or 2.5% sevoflurane. After st eady state end-tidal anesthetic concentrations were maintained for at least 10 min, laryngoscopy and intubation were attempted using a straight-blade laryngoscope and an uncuffed tracheal tube. The interaction between nitrous oxide and sevoflurane was investigated using logistic regression analysis of the responses to intubation. Results: Logistic regression curves of the probability of no movement in re sponse to intubation in the presence of sevoflurane and 0, 33, and 66% nitr ous oxide were parallel. The interaction coefficient between nitrous oxide and sevoflurane did not differ significantly from zero (P = 0.89) and was r emoved from the logistic model. The MAC(TI) (+/- SE) of sevoflurane was 2.6 6 +/- 0.16%, and the concentration of sevoflurane required to prevent movem ent in 95% of children was 3.54 +/- 0.25%. Thirty-three percent and 66% nit rous oxide decreased the MAC(TI) of sevoflurane by 18% and 40% (P < 0.001), respectively. Conclusions: We conclude that nitrous oxide and sevoflurane suppress the re sponses to tracheal intubation in a linear and additive fashion in children .