Diffusion hypoxia: another view.

Arterial oxygen saturation (SaO2) was monitored postoperatively with pulse oximetry in 80 dental patients receiving nitrous oxide and oxygen. These patients were divided into four equal groups, three of which received nitrous oxide (N2O) and oxygen (O2) in ratios of 20:80, 40:60, and 60:40, respectively. The fourth group received 100% O2 and served as the control. The SaO2 was monitored for 15 minutes after termination of the procedure as the patient breathed room air. Continuous pulse oximetry revealed 43 episodes of SaO2 (a decrease greater than 3% from the baseline) in patients who received 20% N2O, 268 episodes in patients who received 40% N2O, 594 episodes in patients who received 60% N2O, and 21 episodes in patients who received 100% O2. The number of patients who experienced desaturation episodes increased with the increase in N2O concentration. The SaO2 values ranged from a decrease of 1.0% to 7.0% with a mean of 2.1%. Smokers experienced a greater number of desaturation episodes in the 40% N2O group and in the control group. One patient in the 40% N2O group experienced an SaO2 of less than 90%, but no patient experienced clinically significant hypoxia. In the 40% and 60% N2O groups, the percent change of SaO2 from the baseline was greater, and the SaO2 returned to baseline slower. The difference in mean SaO2 between smokers and nonsmokers was greater in the 40% N2O group.