Haemodynamic changes in caval venous flow distribution occurring during bidirectional cavopulmonary anastomosis operation are still largely unknown.

Transit time flow measurements were performed in 15 cavopulmonary anastomosis operations. Superior and inferior caval vein flows were measured before and after the cavopulmonary anastomosis. Ratio of superior caval vein to overall caval veins flow was calculated.

Mean superior caval vein flow ratio before cavopulmonary anastomosis was higher than previously reported for healthy children. Superior caval vein flow ratio decreased in 14/15 patients after cavopulmonary anastomosis: mean 0.63 ± 0.12 before versus 0.43 ± 0.14 after. No linear correlation between intraoperative superior caval vein pressure and superior caval vein flow after cavopulmonary anastomosis was found. Neither Nakata index nor pulmonary vascular resistance measured at preoperative cardiac catheterisation correlated with intraoperative flows. None of patients died or required a take down.

The higher mean superior caval vein flow ratio before cavopulmonary anastomosis compared to healthy children suggests flow redistribution in univentricular physiology to protect brain and neurodevelopment. The decrease of superior caval vein flow ratio after cavopulmonary anastomosis may reflect the flow redistribution related to trans-pulmonary gradient. The lack of correlation between superior caval vein pressure and superior caval vein flow could be explained by limited sample size and multifactorial determinants of caval veins flow, although pressure remain essential. Larger sample of measurements are needed to find flow range potentially predictive for clinical failure. To authors’ knowledge, this is the first intraoperative flow measurement of both caval veins during cavopulmonary operations.