Long-term extracorporeal blood bypass in dogs at low flows without systemic heparinization. Heparin-coated versus...

A blind, randomized study of the effects of a heparin-coated bypass circuit on thromboembolus formation and hematologic and hemostatic parameters was carried out on 12 dogs. The dogs were anesthetized and bypassed for 24 hours using a centrifugal pump circuit with a mean flow of 475 ml/minute. Six of the dogs were bypassed with a heparin coated circuit and six with an uncoated circuit. No systemic heparin was administered to any of the dogs at any time during the procedure. Both the coated and uncoated circuits remained patent at low flows. Thrombus formation, however, primarily around the pump axis, was observed in both groups. Four of the dogs (two from either group) had no evidence of lung emboli. The remaining eight dogs all showed pulmonary emboli. Thromboemboli did not lead to clinical complications or hemodynamic disturbances. Hematologic and hemostatic parameters showed a reduction in hemoglobin, erythrocytes, thrombocytes, leukocytes, and antithrombin III, which was most pronounced in the uncoated group. This study showed that a low flow bypass circuit remains patent for 24 hours whether or not the circuit is coated with heparin. Although the heparin coating limits the reduction in antithrombin III and blood elements, it does not eliminate the risk of thromboembolus formation.