[The influence of maternal oxygen inhalation for 30 to 60 minutes on fetal oxygenation]

Healthy parturients with uterine displacement received oxygen inhalation before and during spinal anesthesia for elective cesarean section. Oxygen was administered through a mask (group OH2 : 20 cases) or via a nasal cannula (group OH1: 20 cases) for 33 to 69 minutes. All patients were in the right lateral position prior to spinal block and were in the left tilt after the anesthesia. The fetal blood-gas values were relatively evaluated among the OH2, OH1 and OH groups which received oxygen via a cannula for 9 to 17 minutes. The maternal artery PO2 values for the OH2 group (the mean: 491.7 +/- 61.4mmHg) were significantly higher than those for the OH1 and OH groups (244.5 +/- 28.0 and 225.0 +/- 62.9mmHg, respectively). The umbilical vein PO2 (46.1 +/- 7.5mmHg) and SO2 (87.6 +/- 6.3%) of the OH2 group were also significantly greater than those of the other groups (PO2: 36.1 +/- 4.1mmHg, SO2: 77.3 +/- 6.0% in the OH1 group and PO2: 37.5 +/- 6.4mmHg, SO2: 77.6 +/- 10. 3% in the OH group, respectively). The Apgar scores and both the maternal and fetal acid-base values for all groups were excellent. The umbilical vein to artery PO2 and SO2 gradients of the OH2 group were significantly greater than those of the other groups. It is emphasized that maternal hyperoxia with uterine displacement improves fetal oxygenation without adversely affecting the fetal acid-base state, even if it is excessive and maintained for 60 minutes.