Veno-venous bypass in liver transplantation: heparin-coated perfusion circuits reduce the activation of humoral defense systems in an in vitro model

Abstract

We studied the effects of bypass circuit surface heparinization on kallikrein-kinin, coagulation, fibrinolytic and complement activation in a closed model system for simulating veno-venous bypass (VVBP) in orthotopic liver transplantation (OLT). The circuits were identical to those in routine use during clinical OLT in our institution. Fresh whole human blood diluted 1: 2 with Ringer’s acetate was circulated at a non-pulsatile flow (2 l/min) and at a constant temperature (37.5°C) for 12 h. In 10 experiments, the entire inner surface of the circuits was coated with end-point attached heparin (HC). In the remaining 10, non-treated PVC tubing was used (NC). Components of the plasma kallikrein-kinin, coagulation, fibrinolytic and complement systems were analyzed using functional techniques (chromogenic peptide substrate assays) and enzyme immunoassays at baseline, 3 and 12 h. Significant activation of the initial (C3bc) and terminal (TCC) components of the complement system were found in both the NC and HC groups after 3 and 12 h: C3bc: NC: baseline =4 (3.5-7.7), 3 h=17.3* (12.5-27), 12 h=31* (17.7-63.6), HC: baseline=4.9 (3.2-6.8), 3 h=9* (6-14.4), 12 h=13.7* (7.4-18.1). TCC: NC: baseline=0.4 (0.2-0.6), 3 h=5* (0.8-11.9), 12 h: 13.1* (4.2-25.7). HC: baseline=0.5 (0.1-0.6), 3 h=0.6* (0.1-0.8), 12 h=1.2* (0.3-2) AU/ml; median and range (*: p<0.05). The C3bc and TCC concentrations were significantly higher in the NC group at 3 and 12 h, compared to the HC group: C3bc (NC vs. HC group): 3 h, p<0.001; 12 h, p<0.001. TCC (NC vs. HC group): 3 h, p<0.001; 12 h, p<0.001. Significant increases in the values of thrombin-antithrombin complexes ( p<0.003), prothrombin fragment 1+2 ( p<0.006) and plasmin-α2-antiplasmin complexes ( p=0.016) were found in the non-coated group, but not in the heparin-coated group during the observation period, showing that the coagulation and fibrinolytic systems were activated in the non-coated circuits. We conclude that heparin-coating of the internal surface of the extracorporeal perfusion circuit used for VVBP reduces activation of the plasma cascade systems in a closed venous system in vitro.