Thrombogenicity is not reduced when heparin and phospholipid bonded circuits are used in a rabbit model of extracorporeal circulation.

In an effort to better mimic the thromboresistive nature of vascular endothelium, extracorporeal circuits bonded with heparin or phospholipids were developed. Using no systemic heparinization, these circuits were compared with standard poly(vinyl)chloride (PVC) (Tygon) in a rabbit model of extracorporeal circulation (ECC). Control circuits were run with and without systemic heparinization and used as comparison groups against the test circuits. Two New Zealand White rabbits were used per study: One was used as the platelet donor for 111Indium platelet labeling; the other animal was placed on bicaval ECC for 4 hours. Circuits (heparin coated n = 6, phospholipid coated n = 8, nonheparinized controls n = 14, heparinized controls n = 18) consisted of 1 m of tubing, two downsizing connectors, and two venous cannulae. ECC blood flow was at least 75 ml/min. Platelet and fibrinogen measurements were made hourly, and circuit dosimetry was performed at the end of the study or on circuit thrombosis. Thrombosis of the circuit occurred in one heparin coated, two phospholipid coated, and eight nonheparinized control circuits. None of the heparinized control circuits thrombosed. There was no significant difference between the groups with regard to platelet count or platelet adhesion. Test circuits exhibited preservation of fibrinogen levels. In this rabbit model of ECC, circuits coated with heparin or phospholipids appeared to preserve fibrinogen levels but did not reduce platelet adhesion or consumption.