Blood gas tensions and acid-base status in the fetal guinea-pig.

To establish reference values for blood gas tensions in the fetal guinea-pig, blood was obtained by cardiac puncture or by puncture of the umbilical vein and analysed for pH, PCO2, PO2, haemoglobin concentration (Hb), oxyhaemoglobin saturation (SO2), and packed red cell volume. The measurements were made near term of pregnancy, on the 61st-66th day, and the dams were anaesthetized with diazepam and sodium pentobarbitone. In the umbilical venous blood, mean values for pH, PCO2, PO2, Hb and SO2, respectively, were 7.324, 45.1 mmHg, 29.5 mmHg, 8.8 mmol 1(-1), and 0.57 mol O2 per mol of haemoglobin monomer. The corresponding values for arterial blood from the heart were 7.265, 53.4 mmHg, 18.6 mmHg, 9.2 mmol 1(-1) and 0.25. Thus, blood gas tensions in the fetal guinea-pig are much closer to those of fetal primates and ungulates than has been recognized previously.