Patency of heparinized SBS shunts at high shear rates.

The patency of 50 cm long, 1.7 mm ID heparin-polyvinyl alcohol (PVA) coated SBS arterio-venous shunts in pigs at shear rates greater than 1000 s-1 was found to be not different from that of identical shunts coated with PVA but without heparin. This was attributed to the absence of any measureable effect of surface bound heparin on platelet related thrombus formation at high shear rates. On the other hand, platelet adhesion values determined in the absence of flow by the open static method decreased with increasing heparin content in heparin-PVA films. The low overall patency (average life of 170 minutes) of the PVA coated SBS shunts (with and without heparin) was presumed to be related to the absence of circulating heparin during surgery and the consequent presence of tissue thromboplastin or cellular debris during the immediate postoperative period. Alternative protocols are needed to test heparinized materials at low shear rates in the absence of systemic heparin to properly assess the potential thrombo-resistance of such materials.