Preoxygenation during Pregnancy in the Head-up versus  the Supine Position

I read with interest the article of Dixon et al.  1The results show in the class III obese patients that preoxygenation in the 25° head-up position achieves 23% higher oxygen tensions, allowing a clinical increase in the desaturation safety period. The report postulated that preoxygenation in the head-up position may be advantageous in many other clinical circumstances in which respiratory function may be impaired in the supine position, e.g. , advanced pregnancy, ascites, bowel obstruction.

Baraka et al.  2(1992) reported about “Preoxygenation of Pregnant and Nonpregnant Women in the Head-up versus Supine Position.” The results showed that after 3 min of preoxygenation, desaturation to 95% during subsequent apnea, as monitored by pulse oximetry, was more rapid in pregnant than in nonpregnant patients. Also, changing from the supine to the 45° head-up position prolonged the desaturation time in the nonpregnant women but had no significant effect in the pregnant women (table 1). These results were unanticipated because a change from the supine to the sitting position has been shown to increase the functional residual capacity in both pregnant3and nonpregnant patients.4Baraka et al.  postulated that adopting the 45° head-up position rather than the sitting position may not significantly increase the functional residual capacity in the pregnant woman at term, because the gravid uterus at term may not allow a significant descent of the diaphragm in the head-up position.

American University of Beirut, Beirut, Lebanon. abaraka@aub.edu.lb