Why the study?
Does preoxygenation in the 45 degrees head-up position compared to the supine position increase the duration of apnea before desaturation to 95% in pregnant and nonpregnant women?
Does preoxygenation in the 45 degrees head-up position compared to the supine position increase the duration of apnea before desaturation to 95% in pregnant and nonpregnant women?
The 45-degree head-up position extends the safe duration of apnea before desaturation in nonpregnant women but does not provide the same benefit in pregnant women at term.
May extend safe apnea time with head-up preoxygenation in nonpregnant women; leaves open benefit in term pregnancy.
The influence of preoxygenation in the supine (n = 10) versus the 45 degrees 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.
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Baraka et al. (1992) studied this question.