Heart rate and blood pressure response and metabolic changes in the sheep fetus following reduction of uterine blood flow

Abstract

The cardiovascular and metabolic responses during acute fetal hypoxia were studied in 7 pregnant sheep near term. Complete reduction of uterine flow (UBF) for 180 s was performed in 13 experiments by inflating a balloon positioned in the maternal aorta. Fetal heart rate (FHR), systolic and diastolic blood pressure (BP) and fetal arterial oxygen saturation (SO2) were measured continuously. Blood samples were taken at short intervals and analyzed for pH, PCO2, PO2, SO2, base excess and lactate. Following the reduction of UBF, FHR began to rise after 4.7 +/- 14.4 (SD)s and fell after 31.3 s paralleled by the rise of the BP after 23.2 +/- 8.2 (SD)s. The fall of FHR was not related to the SO2 at control, but to the decline of the SO2 by 10-15%. There was no critical limit of SO2 at which the FHR started to fall and the BP began to rise. The rise of the FHR after UBF had been released was significantly correlated to the rise of SO2. Lactate production during hypoxia was related to the slope of the SO2 decline, i.e., to the fetal O2 consumption. The total metabolic response during hypoxia and recovery given by the pH area was correlated to the SO2 at control. No correlation between dip area of FHR and PH area could be established.