Clotting factor activities and coagulation screening tests in 36 massively transfused patients were measured after every 12 units of blood and whenever diffuse microvascular bleeding (MVB) developed. Moderate deficiencies in clotting factors were common, but they were not associated with MVB. MVB was associated with severe abnormalities of coagulation, i.e. a fibrinogen level less than 0.5 g/l or clotting factor levels less than 20%. The quantitative relationship between the prothrombin (PT) and partial thromboplastin (PTT) times and underlying clotting factor levels was explored by multiple linear regression. Clotting factor levels accounted for only 65-85% of the variability in these tests. However, clotting factor activities less than 20% were reliably reflected by marked prolongations of the PT and PTT (values greater than 1.8 times control). Our data suggest that commonly used replacement formulas are not likely to prevent MVB, since consumption of platelets and/or clotting factors, rather than simple dilution, is a major cause of the deficiencies leading to MVB. Modified whole blood alone was sufficient replacement therapy for most patients. Guidelines for transfusion of supplemental components during massive transfusion are given.

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