Pathogenetic mechanisms of venous congestion after the Fontan procedure

The hemodynamic status after a Fontan type procedure for definitive palliation of functionally univentricular hearts is dominated by a high central venous pressure, which seems to be one of several factors responsible for venous congestion appearing as a frequent complication in the early and late postoperative course. The purpose of our study was to find other hemodynamic parameters correlating with the presence of venous congestion and effusions in these patients.

We compared the hemodynamic data of 18 patients who had an uneventful long-term course after a Fontan type procedure with the respective data of 10 patients who developed symptoms of venous congestion in the immediate postoperative period. Based on a theoretical model, we developed an algorithm to calculate mean hydrostatic capillary pressure from mean arterial pressure, systemic vascular resistance index and central venous pressure.

Pulmonary vascular resistance index (2.1 +/- 1.0 mmHg L-1 min m2), mean left atrial pressure (9.7+/-4.0 mmHg) and cardiac index (3.6+/-0.6 l/min/m2) are mainly normal in patients with venous congestion in the immediate postoperative period, but mean hydrostatic capillary pressure is significantly higher compared to patients without venous congestion (24.3+/-3.1 vs 18.3+/-4.0 mmHg). Lower mean hydrostatic capillary pressures in these patients are due to a highly significant increase of systemic vascular resistance index (18.6+/-4.2 versus 33.6+/-6.6 mmHg L-1 min m2) and a concomitant decrease of cardiac index to 2.4+/-0.3 l/min/m2.

The increase of mean hydrostatic capillary pressure, caused by high central venous pressures but also by relatively low systemic vascular resistance indexes, seems to be the hemodynamic key parameter responsible for venous congestion and effusions in patients after a Fontan type procedure in the immediate postoperative period.