Vacuum-Assisted Venous Drainage during Fetal Cardiopulmonary Bypass

Background: Fetal bypass presents several perfusion challenges, including the need for high arterial flow rates using flexible arterial and small venous cannulae. We hypothesized that vacuum-assisted venous drainage (VAVD) would improve drainage and allow perfusion at higher flow rates which are thought to prevent placental dysfunction induced by fetal bypass.

Methods: We conducted bypass for 60 minutes in 14 fetal lambs (90-105 days gestation; approximately 1-1.5 kg) using a roller pump and various angled venous cannulae (8-12 Fr). VAVD at -20 mm Hg or -40 mm Hg was compared with gravity drainage.

Results: Average flow using gravity drainage was 139 ml/kg/min; after VAVD, we achieved average flows of 285 ml/kg/min (range, 109-481 ml/kg/min). VAVD at -40 mm Hg caused right atrial trauma in four fetuses; no injury was seen at -20 mm Hg. Venous air entrainment during repair of the injuries did not result in any apparent air embolism. Spontaneous pulmonary hemorrhage occurred in two fetuses at the highest flows (>/= 400 ml/kg/min). In all but one case, termination of bypass was followed by placental dysfunction within 120 minutes.

Conclusion: VAVD can be safely applied during fetal bypass provided pressures are kept