Finding the bleeding edge: 24-hour mortality by unit of blood product transfused in combat casualties from 2002-2020

BACKGROUND Transfusion studies in civilian trauma patients have tried to identify a general futility threshold. We hypothesized that in combat settings there is no general threshold where blood product transfusion becomes unbeneficial to survival in hemorrhaging patients. We sought to assess the relationship between the number of units of blood products transfused and 24-hour mortality in combat casualties. METHODS A retrospective analysis of the Department of Defense Trauma Registry supplemented with data from the Armed Forces Medical Examiner. Combat casualties who received at least one unit of blood product at US military medical treatment facilities (MTFs) in combat settings (2002-2020) were included. The main intervention was the total units of any blood product transfused, which was measured from the point of injury until 24 hours after admission from the first deployed MTF. The primary outcome was discharge status (alive, dead) at 24 hours from time of injury. RESULTS Of 11,746 patients included, the median age was 24 years, and most patients were male (94.2%) with penetrating injury (84.7%). The median injury severity score was 17 and 783 (6.7%) patients died by 24 hours. Median units of blood products transfused was 8. Most blood products transfused were red blood cells (50.2%), followed by plasma (41.1%), platelets (5.5%), and whole blood (3.2%). Among the 10 patients who received the most units of blood product (164 units to 290 units), 7 survived to 24 hours. The maximum amount of total blood products transfused to a patient who survived was 276 units. Of the 58 patients who received over 100 units of blood product, 20.7% died by 24 hours. CONCLUSION While civilian trauma studies suggest the possibility of futility with ultra-massive transfusion, we report that the majority (79.3%) of combat casualties who received transfusions greater than 100 units survived to 24 hours. These results do not support a threshold for futility of blood product transfusion. Further analysis as to predictors for mortality will help in situations of blood product and resource constraints. LEVEL OF EVIDENCE Prognostic and Epidemiological; Level IV.