PROBLEMS IN HEMOSTASIS WITH EXTRACORPOREAL APPARATUS

When an extracorporeal circulation is employed, the patient’s blood must be rendered incoagulable with heparin. This necessary state of incoagulability may become a serious threat to the life of the patient. Postoperative difficulty with hemostatis when an extracorporeal apparatus has been used is not uncommon. A surgeon performing open-heart operations must, therefore, be prepared to deal with an occasional difficult problem of continued postoperative bleeding. A single simple defect in the coagulation mechanism may be present which can be quickly and easily corrected. On the other hand, there may be multiple defects in the coagulation process, making the task of restoring normal coagulability complex and difficult. Finally, the worst problem of all is when the hematologist has performed every test on the patient’s blood known to his esoteric a r t and reports: “Nothing is the matter with the patient’s blood except that it won’t clot.” We will assume in the following discussion that preoperatively there was no hematologic disorder and no abnormal capillary fragility. We shall also assume that there has been no incompatibility between the blood in the circuit, the blood transfused during the operation, and the patient’s blood. Trauma to the blood is probably the most important factor in the development of a bleeding diathesis af ter employing an extracorporeal blood circuit.11 The concentration of free hemoglobin in the plasma is a rough index of the degree of trauma to the erythrocytes, and hence to other components of the blood. I t is not a quantitative index of the amount of hemolysis, however, as the free hemoglobin in the plasma is continually being removed by the kidneys. However, the greater the observed hemolysis, the greater the chance that a bleeding diathesis will develop. Since the degree of trauma to the blood with any extracorporeal apparatus varies directly with the duration of the perfusion, patients who have had long perfusions are more likely to bleed postoperat‘ively.” Extracorporeal blood circuits should be designed to diminish trauma to the blood caused by excessive turbulence. “Jet effects,” passage of blood at high speed from a narrow conduit into a wide one, a r e particularly injurious to the cellular elements of the blood and should be avoided. Return of blood from the patient to the extracorporeal apparatus by the so-called “coronary-sucker” system may injure erythrocytes, especially if large amounts of a i r are aspirated with the blood.“