Additive Contribution of Nitrous Oxide to Sevoflurane Minimum Alveolar Concentration for Tracheal Intubation in Children

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Abstract
Background: To study the interaction between nitrous oxide and sevoflurane during trachea intubation, the authors determined the minimum alveolar concentration 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% sevoflurane; or 66% nitrous oxide with 1.0, 1.5, 2.0, or 2.5% sevoflurane. After steady 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 response to intubation in the presence of sevoflurane and 0, 33, and 66% nitrous oxide were parallel. The interaction coefficient between nitrous oxide and sevoflurane did not differ significantly from zero (P = 0.89) and was removed from the logistic model. The MAC(TI) (+/- SE) of sevoflurane was 2.66+/-0.16%, and the concentration of sevoflurane required to prevent movement in 95% of children was 3.54+/-0.25%. Thirty-three percent and 66% nitrous 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 responses to tracheal intubation in a linear and additive fashion in children.