VARIABILITY OF CONTINUOUSLY MEASURED ARTERIAL PH AND BLOOD-GAS VALUESIN THE NEAR-TERM FETAL LAMB

In fetal sheep, arterial blood gas values show considerable spontaneou s fluctuations. The aim of the present study was to obtain quantitativ e data on fetal blood gas variability. Accurate assessment of the intr aindividual variations can hardly be obtained from intermittent blood samples, but requires continuous measurement. For this purpose we deve loped a small extracorporeal flow-through cuvette, containing pH and b lood gas electrodes and the fiber optic probe of an oximeter. The cuve tte is connected through two catheters to the fetal circulation. Blood from the carotid artery flows through the cuvette at a constant rate of 2 mL/min and is drained into the jugular vein. Continuous recording s for 6 h were obtained from five chronically instrumented sheep fetus es at 134-137-d gestational age. Intraindividual variability of fetal arterial blood pH (pHa), partial pressure of arterial blood CO2 (Pace, ) and O-2 (Pao(2)), and saturation of arterial blood (Sao(2)) is quant itatively described. The individual variation coefficients ranged from 0.1 to 0.4% (pHa), from 1.4 to 7.6% (Paco(2)), from 2.5 to 5.5% (Pao( 2)), and from 3.6 to 7.0% (Sao(2)). The 5th to 95 percentile intervals (a) of the individual blood gas values ranged from 0.03 to 0.09 (pHa) , from 0.3 to 1.6 kPa (Paco(2)), from 0.22 to 0.5 kPa (Pao(2)), and fr om 10.5 to 26.0% (Sao(2)), These findings indicate that considerable f luctuations in fetal arterial blood gases occur during a 6-h period, T hese fluctuations are associated with uterine contractures and changes in maternal and fetal activity.