SOME VARIABLES AFFECTING HEMOSTASIS IN CARDIOPULMONARY BYPASS *

Blood We will not be concerned with the platelets or plasma a t this point. Rather we will examine the influence of the patient’s hematocrit on estimates of hemostasis. In a signficant number of cases, the patient comes to operation with an abnormally elevated hematocrit particularly with congenital defects. For example, a case of Tetralogy of Fallot verified a t operation. The patient was minimally symptomatic with marked cyanosis of lips, mouth, fingernails, and toenails. The patient had a preoperative hematocrit of 75 per cent. Preoperative estimates of hemostasis done in the routine laboratory I wish to emphasize this point again done in the routine laboratory, were reported as abnormal. The Lee-White whole blood clotting time was said to be four hours or more, and the prothrombin time was repeated several times with results of 10 per cent, 15 per cent, and below 10 per cent. Though the patient exhibited no petechiae, purpura, hematomae, or bleeding from venipuncture sites, these laboratory estimates of coagulability were sufficient to contraindicate surgery. The point to be made is this : blood with a hematocrit of this value required special laboratory manipulation in order to correctly perform the tests of clotting function. Since the plasma volume was approximately one-half that of normal, the plasma samples handled in a routine fashion by the routine laboratory contained twice as high an anticoagulant concentration. The amount of concentration of calcium routinely admixed with the plasma to perform various coagulation tests in the laboratory was inadequate, leading to false low values. Thus, for example, a result of 6 per cent of normal was obtained, when such blood was handled routinely -whereas its actual percentage was 55 per cent. In addition, the greatly increased red cell mass does have a special