Renal responses to prolonged (48 h) hypoxemia without acidemia in the late-gestation ovine fetus

The effect of sustained moderate hypoxia on renal blood flow and renal func tion was studied in the ovine fetus (123-129 days). The experiments consist ed of 48 h of isocapnic hypoxia, not resulting in acidemia, but sufficient to produce redistribution of blood flow in favor of the brain at the expens e of the car cass. Hypoxemia was induced by maternal nitrogen inhalation. F etal arterial O-2 saturation and arterial O-2 pressure (Pa-O2) decreased fr om, respectively, 50.6 +/- 3.0% and 17.2 +/- 0.9 mmHg during control to 36. 4 +/- 2.7% and 13.4 +/- 0.7 mmHg on the first and to 32.2 +/- 2.2% and 12.4 +/- 0.7 mmHg on the second day of hypoxemia. Fetal renal blood flow and ur ine production rate were continuously measured using ultrasonic flow transd ucers. Fetal renal blood flow increased during hypoxemia from 11.8 +/- 1.6 to 15.6 +/- 1.8 ml/min and remained elevated throughout the 48-h hypoxemia period (P < 0.01). Renal blood flow was inversely correlated with fetal Pa- O2 (r is -0.69, P < 0.0001). Fetal urine production rate, glomerular filtra tion rate, filtration factor, osmotic clearance, and free water clearance d id not significantly change from control values during hypoxemia or recover y. We conclude that hypoxemia without acidemia results in an immediate and considerable increase in fetal renal blood flow, which remains elevated for the entire hypoxemic period.