Maternal inspired oxygen concentration and fetal oxygenation during caesarean section

This study was designed to determine whether fetal arterial and venous PO2 could be increased by increasing maternal FIO2 in the period between hysterotomy and birth. Two groups of ten patients were studied. All were anaesthetised with the same technique except for the FIO2 after hysterotomy. One group inspired 50% oxygen and the second group inspired 100% oxygen. Although the maternal arterial PO2 was higher at birth in the 100% O2 group (177.4 +/- 42.3 mmHg vs 281.0 +/- 94.2 mmHg), there were no differences between the arterial umbilical cord PO2 (19.3 +/- 5.7 mmHg vs 18.5 +/- 7.3 mmHg) and the venous umbilical cord PO2 (31.1 +/- 7.6 mmHg vs 33.0 +/- 10.8 mmHg). Awareness was present in one patient in the 50% O2 group and in four patients in the 100% O2 group but this difference was not statistically significant. It is concluded that a higher inspired maternal oxygen concentration between hysterotomy and birth does not result in any increase in fetal PO2.