Changes in aortic distension waveforms in acute hypoxemia and acidosis: fetal lamb study.

The objective was to investigate the relationship between fetal aortic distension waveforms and fetal hypoxemia and/or acidosis. Aortic distension waveforms were recorded using an echo-tracking system in nine late-gestation catheterized fetal lambs. Under hypoxic conditions induced by inhalation of gas mixture, fetal blood pressure and aortic distension waveforms were recorded. Four parameters, namely peak systolic and end diastolic diameter, amplitude (DeltaD) and ratio of DeltaD to end diastolic diameter (%DeltaD), were obtained, and correlations between these parameters and partial arterial oxygen tension (PaO(2)) and pH of fetal blood gas were analyzed. These four parameters were compared between the control, hypoxemic and asphyxic groups. The DeltaD and %DeltaD were significantly correlated with PaO(2) and pH using linear regression analysis. Both the DeltaD and %DeltaD decreased significantly, in a stepwise fashion, in the hypoxemic and asphyxiated groups compared with controls using repeated measured analysis of variance. It was concluded that fetal aortic distension waveforms proved to be a useful tool to detect the deterioration in the fetal circulation secondary to intrauterine hypoxemia/asphyxia.