Pump-induced platelet aggregation in albumin-coated extracorporeal systems

Objective: Coating of extracorporeal systems with heparin does not prevent platelet activation and subsequent bleeding disorders. We investigated whet her this could be due to elevated shear stress caused by a roller pump. Met hods: Human or rat blood was made to flow through an uncoated or an albumin -coated medical polyvinyl chloride tube with or without a roller pump. Aggr egation of platelets in the tubing was recorded continuously with a photome tric device. Results: Although in vitro gravitational flow in uncoated tube s caused immediate platelet aggregation and platelet loss, this remained ab sent in coated tubes. When the pump was started in experiments with a coate d tube strong platelet aggregation was observed and platelet count fell wit hin 5 minutes to 78% +/- 2% and 71% +/- 3% of control values in human and r at blood, respectively. In vivo, no aggregation was observed during spontan eous now in rats with an albumin-coated tube running from the carotid arter y to the femoral artery, but aggregation started as soon as the blood was p umped. Pump-induced platelet aggregation, both in vitro and in vivo, could be prevented with aurintricarboxylic acid, which specifically inhibits shea r-induced platelet aggregation as has recently been shown. Pump perfusion o f blood in an uncoated tube did not elicit platelet aggregation. Conclusion s: Pump perfusion of blood in coated systems elicits shear-induced platelet aggregation, which may be prevented by administration of substances that b lock the binding of von Willebrand factor to glycoprotein Ib receptors on t he platelets, The effects of pumping on platelets are masked in uncoated ci rcuits because of the dominant influence of blood-material contact.