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 fetal lamb. Methods: With the ewe given inhalation anesthetics, eight chronically instrumented intrauterine fetal lambs at 125-135 days' gestation were given normal saline fluid boluses. Inferior vena cava peak pressures and umbilical venous Doppler velocities were measured before, during, and after administration of normal saline. Pressures were obtained 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 administered. 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 decreased (P < .03). Conclusion: Umbilical venous Doppler velocity pulsations developed after fluid administration and were associated with increases in inferior vena cava peak pressure. These findings suggest that umbilical venous pulsations develop when fetal venous pressures are elevated.