UMBILICAL VENOUS DOPPLER VELOCITY PULSATIONS AND INFERIOR VENA-CAVA PRESSURE ELEVATIONS IN FETAL LAMBS

Objective: To examine effects of fluid administration on inferior vena cava pressure and umbilical venous Doppler velocities in the term fet al lamb. Methods: With the ewe given inhalation anesthetics, eight chr onically instrumented intrauterine fetal lambs at 125-135 days' gestat ion were given normal saline fluid boluses. Inferior vena cava peak pr essures and umbilical venous Doppler velocities were measured before, during, and after administration of normal saline. Pressures were obta ined with fluid-filled and solid state pressure transducers. Results: Umbilical venous Doppler velocity pulsations developed in six fetuses after 120 mL and all eight fetuses after 240 mL of fluid were administ ered. Inferior vena cava peak pressure increased from 5.15 +/- 2.7 to 10.9 +/- 3.9 mmHg (P < .001). Heart rate did not change significantly, and umbilical arterial systolic-to-diastolic velocity ratios decrease d (P < .03). Conclusion: Umbilical venous Doppler velocity pulsations developed after fluid administration and were associated with increase s in inferior vena cava peak pressure. These findings suggest that umb ilical venous pulsations develop when fetal venous pressures are eleva ted.