PATHOLOGICAL FIBRIN FORMATION AND COLD-INDUCED CLOTTING OF MEMBRANE OXYGENATORS DURING CARDIOPULMONARY BYPASS

In 1,800 patients undergoing cardiac surgery over a P-year period, 11 incidents of abnormal inlet pressure elevations occurred before the me mbrane oxygenators. In 3 patients, the oxygenators had to be changed d uring cardiopulmonary bypass. This complication was found to be caused by fibrin formation possibly secondary to precipitaition of fibrinoge n with other coagulation factors in the heat exchangers of the oxygena tors during the cooling phase. Large amounts of fibrin were demonstrat ed in the heat exchanger of the oxygenators. After careful washing of the apparatus, plasmin was added and fibrin was detected by measuring D-dimer levels. In heat exchangers from uneventful operations, only tr ace amounts of fibrin were found. Because there were no cold agglutini ns demonstrated in the patients before surgery, cryoprecipitation stud ies were performed soon after surgery. When the patients' plasma sampl es were studied at different temperatures, from 37 degrees C down to 3 degrees C, cryoprecipitates or a gel (in 1 patient only) were formed. This indicated that there might be something abnormal with regard to fibrinogen fibrin formation. The study patients were therefore investi gated after the acute phase of the operation had ended for various coa gulation factors, as well as for fibrin gel network characteristics. T he results were compared with those of a control group (n = 10) with u neventful operations. There were no differences between the groups wit h regard to levels of coagulation factors VII and VIII and von Willebr and factor, although they were increased in both groups. The mean leve ls of coagulation inhibitors, antithrombin and Protein S, were slightl y lower in the study patients. All of these patients had a highly path ologic, ie, tight fibrin gel network, except for the patient in whose sample a gel formed, despite being treated with aspirin or oral antico agulants. The network was also tighter in some of the controls (v midd le-aged reference individuals), although it was significantly tighter in the patients. It is concluded that some individuals who have an inc reased tendency to form tighter fibrin gel networks might be at increa sed risk for a severe complication during cardiac surgery performed un der hypothermia. Copyright (C) 1995 by W.B. Saunders Company