Nitrous Oxide Effects the Uptake of Sevoflurane to the Body During Induction

Abstract

Objective: To determine the effects of nitrous oxide (N2O) on the speed and quality of the uptake process of sevoflurane during inhalation induction in adult patients. Materials and Methods: For randomized controlled study, eighty-four American Society of Anesthesiologists I-II patients undergoing gynecological interventions were randomly assigned to receive an 8\% sevoflurane mixture with either 67\% N2O plus 33\% oxygen {[}Group sevoflurane and nitrous oxide (SA)] or 100\% oxygen only {[}Group sevoflurane (S)]. Both groups were induced by a single-breath induction. End-tidal and inspiratory concentrations of respiratory and anesthetic gasses were continuously assessed during induction as well as time to loss of eyelash reflex, time to cessation of eye movements, and time to initiation of spontaneous breaths. Patients were intubated by the 5th minute of induction and their vital signs, bispectral indexes, reflex responses to intubation and additional drug requirements for intubation were also recorded. Results: End-tidal sevoflurane concentrations and the ratio of alveolar to inspiratory sevoflurane concentrations (F-A/F-i) of patients in group SA recorded at the 2nd, the third and the 5th minute of induction showed statistically significant increases when compared with patients in group S. Time to loss of eyelash reflex and time to cessation of eye movements were found to be decreased in group SA by 25 and 13\%, respectively. Patients who presented with a reflex response to intubation in group S exceeded patients in group SA by 38.8\% and patients who required additional medication for intubation in group S exceeded patients in group SA by 28.6\%. Conclusion: The findings of this study support the view that administration of N2O improves the rate and quality of mask induction with sevoflurane. The benefits provided by N2O attributable to the concentrating and second gas effects appear during the first few minutes of induction (2nd, 3rd, and 4th minutes) as well as during intubation when sevoflurane is used for mask induction.