Severe bleeding is commonly encountered in surgery, trauma, gastrointestinal hemorrhage and obstetrics and may require massive transfusion (MT). A universal definition of what constitutes a MT, however, is not well defined. Historically, MT has been loosely defined as transfusion of >10 units of whole blood or RBCs within 24 hours, which is approximately >1 total blood volume for an adult. Other definitions of MT account for patients who die before 24 hours or the transfusion of other blood products besides red blood cells or whole blood. A new systematic review was performed to characterize the definitions of MT that researchers are using in randomized controlled trials (RCTs). Over 8,400 manuscripts related to MTs were screened, and 30 RCTs were identified [19 published (1986-2022) and 11 ongoing] that defined MT and were based on adult patients at risk for MT. A total of 15 MT definitions were identified in four different clinical settings—trauma, obstetrics, cardiothoracic surgery and orthopedic surgery. Overall, the most common MT definition was >10 units of RBCs transfused in 24 hours (9/30—all published studies). More recent RCTs tended to define MT as three to five units of RBCs in one to six hours—lower RBC volumes and shorter time frames. The medical community needs to better define MT to better guide clinical practice and future research.
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