Evaluation of fetal and uterine hemodynamics during maternal cardiopulmonary bypass

About 4% of pregnant women have concomitant cardiac disease and a few of these do not respond to medical therapy and require surgical correction during pregnancy. We report a unique case describing fetal hemodynamics and uterine blood flow before, during, and after maternal cardiopulmonary bypass, and compare them to normal reference values in the second trimester.

A woman with severe aortic regurgitation underwent aortic valve replacement at 19 weeks' gestation. A nonpulsatile cardiac pump was used for cardiopulmonary bypass, maintaining the mean arterial pressure at 77-90 mmHg, with a peak flow rate of 3.5-4.0 L/minute/m2 and core temperature of 34-35C throughout surgery. Blood velocity waveforms were recorded by Doppler ultrasound at the level of maternal main uterine artery and fetal vessels. Pulsatility index (PI) values were calculated. Preoperatively, fetal hemodynamic characteristics were within normal limits. Preoperatively, uterine artery PI was 3.9 (normal 0.5-1.5 at 20 weeks). Intraoperatively, fetal bradycardia ensued after aortic clamping (120 to 75 beats per minute), with a rise in umbilical artery PI (1.7 to 7.1) and disappearance of diastolic flow. The middle cerebral artery PI decreased (2.0 to 0.92) and the PI increased in the descending aorta (2.22 to 3.55), inferior vena cava (2.7 to 9.3), and ductus venosus (0.6 to 1.7). During bypass, after aortic clamping, nonpulsatile uterine artery flow was noted. Postoperatively, the uterine artery PI improved, to 1.0. Two days later, hydrocephalus and hydrops were observed.

Despite high peak flow rates, normal mean arterial pressure, and normothermia, fetal outcome was dismal. Nonpulsatile cardiopulmonary bypass under normothermia may not be able to meet the demands of the fetoplacental circulation.