Preoxygenation of Pregnant and Nonpregnant Women in the Head-Up Versus Supine Position

The influence of preoxygenation in the supine (n = 10) versus the 45° head-up (n = 10) position on the duration of apnea leading to a decrease in arterial oxygen saturation to 95%, as monitored by pulse oximetry, was investigated in 20 women undergoing elective cesarean section at term of pregnancy. The results were compared with those obtained in a control group of 20 nonpregnant women. In the supine position, the average time to desaturation to 95% was significantly shorter in the pregnant group (173 ± 4.8 s [mean ± SD]) than in the control group of nonpregnant women (243 ± 7.4 s). Using the head-up position resulted in an increase in the desaturation time in the nonpregnant group (331 ± 7.2 s) but had no significant effect in the pregnant group (156 ± 2.8 s). We conclude that pregnant women desaturate their arterial blood of oxygen more rapidly than do nonpregnant women. Furthermore, the head-up position extends the duration of apnea that can take place before desaturation occurs in nonpregnant patients.