Definition: replacement of > 1 blood volume (in average adult ≈ 20 U) in < 24 hrs for adult, or > 2 × circulating blood volume in peds, may cause dilution of effective platelets and coagulation factors. When operating on a pediatric patient, you can usually safely replace up to 1.5 × the circulating blood volume before problems with coagulopathy ensue.
Blood component therapy required for massive transfusions:
platelets (4 U in adult)
Red blood cell therapy
Major histocompatibilities of blood are shown in Table 9.2.