[Intervillous blood-gas status, especially oxygenation during cesarean section]

Intervillous (IV), arterial (MA), and umbilical venous (UV) and arterial (UA) blood-gas values were measured in 36 healthy pregnant women. The patients were divided into three equal groups and underwent elective cesarean sections under spinal block. Oxygen was administered through a nasal cannula (group OL) or a mask (group OH), through group RA received no oxygen inhalation. Mean MAPO2 in each group was 102.0, 213.9 and 482.4 mmHg, respectively. Intervillous PO2 (Mean +/- SD mmHg) was 49.0 +/- 7.1 in group RA, 63.1 +/- 14.5 in group OL, 84.6 +/- 25.2 in group OH, oxygen saturation (%) was 83.2 +/- 6.0, 89.6 +/- 5.5 and 94.3 +/- 2.6, respectively, and oxygen content (CO2: ml/dl) was 12.7 +/- 0.9, 13.7 +/- 1.0 and 14.4 +/- 0.5, severely. There were significant differences in the intervillous oxygen values among the three groups. The intervillous acid-base value in group RA (pH: 7.389 +/- 0.013, PCO2: 33.9 +/- 2.3 mmHg and BD: 4.4 +/- 0.9 m mol/l) showed no significant differences from those of the other groups. Mean UVCO2 was somewhat greater than mean IVCO2 in any group due to the relatively higher oxygen affinity of fetal blood. Both IV and UVPO2 were not so elevated with oxygen inhalation and this was assumed to be due to characteristics of the oxyhemoglobin dissociation curve. The other results produce reliable evidence that placental circulation is not affected by maternal hyperoxia and that an increase in (IV-UA)PO2 facilitates oxygen transfer to the fetus.