Arterial oxygen desaturation rate following obstructive apnea in parturients.

This study was attempted to observe the rate of oxygen desaturation after full oxygenation in six parturients scheduled for Cesarean sections and six patients scheduled for transabdominal hysterectomies. We calculated the mean rate of fall of arterial saturation (slope of desaturation: less than SaO2 (t2)-SaO2(t1) greater than/t2-t1) and changes in arterial blood gases were observed. All subjects were denitrogenated then a single isolated apnea was carried out. The mean time to obtain 90% saturation was longer in the nonpregnant group (7.5 min vs 3.6 min in parturients). The mean slope of desaturation was steeper in the parturients (-3.34) than the nonpregnant group (-1.52). As far as the oxygen reserve is concerned, the parturients had a lesser margin of safety than the nonpregnant women. It was concluded that the lower the thoracic gas volume (parturients), the lower the alveolar O2 stores and, the more rapidly these stores are depleted.