THE DUCTUS-ARTERIOSUS, PRE-DUCTAL AND POST-DUCTAL OXYGEN-SATURATION MEASUREMENTS IN FETAL LAMBS

In the fetus, the arterial oxygen saturation (SaO(2)) in the ascending aorta is higher than in the descending aorta. We questioned whether t his difference over the ductus arteriosus (Delta SaO(2)) would change during hypoxaemia. Therefore, six chronically instrumented fetal lambs (119-126) days of gestation) were studied, by changing the inspired o xygen (FlO(2)) via a tracheal tube to the ewe. The SaO(2) was measured intermittently every 15 min with blood samples obtained from the asce nding and descending aorta, and continuously with 2 pulse oximeters at both sides of the ductus arteriosus. Delta SaO(2) was at a level of 3 .4-5.3% and had a tendency to decrease at preductal SaO(2) levels of 1 0-20% and at pH levels below 7.25. The precision of the pulse oximeter s, expressed as standard deviation of the differences between sample S aO(2) and pulse oximeter SaO(2), was around 5.0% for the individual ca libration curves. This precision was not enough to show details of the course of Delta SaO(2) between the blood samples. Our results show th at ther is no change in Delta SaO(2) across the ductus arteriosus.