Clinical Study of Diffusion Hypoxia in Early Period after Nitrous Oxide Anesthesia

Kil, Hae Keum; Kim, Won Oak; Lee, Sung Jin; Lee, Woo Kyung

Abstract

Introduction
Anesthesiologists have been aware of the dangers of diffusion hypoxia in the early postoperative period after nitrous oxide anesthesia, but it was suggested of a little clinical significance in healthy patients. Goal of this study is to re-evaluate the possibility of diffusion hypoxia.
METHODS
Eighty patients who were scheduled for vitrectomy were allocated to two groups by normal and abnormal chest X-ray findings and each group was divided into two subgroups by N2O concentration (1-a, 2-a; 50%, 1-b, 2-b; 60%). One and half hours after anesthesia, end-tidal alveolar concentration of oxygen (et-O2), N2O (et-N2O), and PaO2 were measured for 10 minutes after the inspired gases were changed to room air 2 L/minute with controlled ventilation in group 1-a. Those parameters were re-measured after re-administration of O2 and N2O of 50% of each for an hour and the inpired gases were changed to room air again.
RESULTS
In group 1-a, there was no significant differences of et-N2O and PaO2 after 5 minutes by air flow. And there was no differences of et-N2O and PaO2 between group 1-a and 1-b by et-N2O after 4 minutes. In group 1-b, PaO2 was in normal range at 10 minutes after, although et-O2 was decreased to 14.9%. However, group 2-b showed peripheral arterial saturation lower than 96% after 6 minutes and mild hypoxemia (PaO2 75.3 mmHg) at 10 minutes.
CONCLUSIONS
We suggest that hypoxemic episode during spontaneous breathing of room air in early postoperative period after nitrous oxide anesthesia may be occur due to decreased ventilatory function rather than diffusion of nitrous oxide. However, in patients with minimal abnormal chest X-ray findings even without clinical symptoms, it would be better to avoid high concentration of nitrous oxide.