PROFOUND NORMOVOLEMIC HEMODILUTION - HEMOSTATIC EFFECTS IN PATIENTS AND IN A PORCINE MODEL

Previous systematic investigations of the hemostatic effects of normov olemic hemodilution (NHD) have not explored the influence of hematocri ts less than 20% in humans or animals. However, clinical interest in m aximizing the perioperative conservation of erythrocytes may involve p rofound NHD beyond traditionally accepted empiric end points. We repor t here on coagulation data in eight healthy adolescent patients underg oing profound NHD in concert with surgical correction of idiopathic sc oliosis, and in 29 swine undergoing experimental stepwise NHD until de ath. Blood was replaced with 5% albumin in 0.9% saline in our patients , and with 5% albumin in lactated Ringer's solution in our pigs. A 75% blood volume exchange in our patients yielded a platelet count (PLT) of 158 +/- 26 X 10(3)/mu L, fibrinogen concentration (FIB), 50 +/- 7 m g/dL, prothrombin time (PT), 25.4 +/- 2.6 s, activated partial thrombo plastin time (aPTT), 87 +/- 15 s, and a nadir hemoglobin of 2.8 +/- 0. 2 g/dL; however, global oxygen delivery as assessed by body oxygen con sumption remained adequate. Coagulation during the experimental porcin e hemodilution was assessed by measuring PLT, FIB, PT, and aPTT, as we ll as by measurement of coagulation factor activities. In neither spec ies did clinically significant thrombocytopenia (PLT < 100 X 10(3)/mu L) become manifest prior to clinical or other laboratory evidence of c oagulopathy. Rather, a combined deficiency of coagulation factors expl ains the coagulopathy developing during NHD in both patients and swine . Abnormal hemostasis develops prior to compromise of global tissue ox ygenation, assessed by mixed venous oxygen saturation and total body o xygen consumption, during NHD in healthy patients anesthetized as desc ribed. Therefore, NHD may be more limited by preservation of normal co agulation than of global oxygen delivery and consumption.