Doppler assessment of tracheal fluid flow during fetal breathing movements in cases of congenital diaphragmatic hernia.

OBJECTIVE

The purpose of this investigation was to examine the characteristics of breathing-related fluid flow in the trachea of human fetuses with congenital diaphragmatic hernia in the hopes of developing a standard for the prenatal diagnosis of the degree of severity of the resulting pulmonary hypoplasia. Our ultimate goal is the prediction of postnatal mortality in fetuses with congenital diaphragmatic hernia.

SUBJECTS AND METHODS

The study comprised six cases of isolated congenital diaphragmatic hernia (one on the right side; five on the left) varying in gestational age from 26 to 36 weeks. Four of the patients survived after surgical repair and two died during the neonatal period owing to lung hypoplasia. Color Doppler was used to visualize the fluid displacement in the trachea generated by fetal breathing movements. Spectral Doppler was then used to analyze the fluid flow velocity waveforms. More than 40 continuous breathing cycles (inspiration + expiration) were recorded for each case. We distinguished between regular and irregular patterns.

RESULTS

Only the regular breathing phases, defined as five or more consecutive cycles of symmetric appearance, were considered for analysis. The inspiration and expiration times, the peak velocity of inspired and expired fluid and the volume obtained by integration of the tracheal fluid flow displaced during fetal breathing were compared with those of five healthy fetuses for each gestational age. Only the tracheal volume flow was helpful in predicting outcome. In normal pregnancies this parameter increased from 0.21 +/- 0.10 ml/breath (mean +/- SD) at 26 weeks to 1.37 +/- 0.48 ml/breath at 36 weeks of gestation. A significantly low (p < 0.05) volume flow was found only in the fetuses with congenital diaphragmatic hernia with a lethal postnatal outcome, whereas this parameter was normal in all survivors.

CONCLUSIONS

Our preliminary observations suggest that the tracheal volume flow during fetal breathing activity is related to lung growth. In fetuses with severe lung hypoplasia one would expect a significant reduction in this parameter as an expression of deficient fetal lung growth. The displaced fluid volume per breath in the trachea of human fetuses as assessed by Doppler ultrasound may be a useful predictor of outcome in cases of isolated congenital diaphragmatic hernia.