Cardiopulmonary bypass in ewe's fetus: advances and setbacks in our learning curve

Fetal cardiac surgery represents a surgical challenge and several centers are attempting to establish a suitable methodology in animals. We present our experience with extra-corporeal bypass procedures in preterm and term sheep fetuses. Twenty-two fetuses (103-139 days gestation, mean 115 days gestation) underwent a 1-hour period of right heart-to-pulmonary artery extracorporeal circulation followed by 1 hour of observation. Animals were divided into group 1 and group 2, according to gestational age (above and below 0.85). Three pumps were used: centrifugal without (group 1) reservoir, centrifugal with (group 2) reservoir, and roller with reservoir (group 2). Experiments were completed in 75% of fetuses in group 1 and in 37% of fetuses in group 2. Bleeding was the main cause of failure, especially for group 2. A slow deterioration of blood gas status was noted in group 1, while this trend could be partially reversed in group 2 with corrective measures. Complete heart bypass could not be achieved in either group, and residual fluctuations in arterial pressure were observed. During bypass, body temperature decreased more in group 2 than in group 1. We conclude that cardiac bypass is feasible over a short period in near-term fetuses. A successful outcome may also be obtained in younger fetuses, but better measures need to be implemented for the prevention of surgical bleeding.