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Toward a better definition of massive transfusion: Focus on the interval of hemorrhage control

BACKGROUND In clinical research, massive transfusion (MT) is commonly defined as transfusion of 10 or more red blood cell (RBC) units within 24 hours. However, the clinical relevance of this definition remains poorly understood. In this study, we evaluated whether patients who reach the MT threshold during hemorrhage control differ clinically from those who reach it after hemorrhage control (i.e., after intensive care unit [ICU] arrival) but before 24 hours. METHODS Prospective data were collected on all Level I trauma resuscitations within 5.5 years. Patients transfused 10 or more RBCs in the first 24 hours of hospitalization were identified and stratified according to when the MT threshold was achieved: before ICU arrival (Pre-ICU) versus after ICU arrival but before 24 hours of hospitalization (Post-ICU). Clinical characteristics between groups were compared. RESULTS Three hundred five patients received 10 or more units before ICU arrival, and 46 reached the MT threshold after ICU arrival but before 24 hours. Both groups were clinically similar with respect to age, sex, and Injury Severity Score, but the Post-ICU group had a larger proportion of blunt injuries (71 vs. 53%, p < 0.05), lower mean admission lactate (5.9 vs. 8.1 mmol/L, p < 0.05), and higher systolic blood pressure (112 vs. 96 mm Hg, p < 0.05) compared with the Pre-ICU group. Twenty-four-hour mortality was significantly lower in the Post-ICU group compared with the Pre-ICU group (9 vs. 33%, p < 0.05). In-hospital mortality was not significantly different between groups (33 vs. 46%, p = 0.11). CONCLUSION Patients reaching the MT threshold after ICU arrival comprise a relatively small proportion of those that would be included by the traditional MT definition. However, they have a significantly decreased mortality risk at 24 hours and the potential to dilute the study cohort. For research purposes, restricting the MT definition to 10 or more RBCs during hemorrhage control may result in study cohorts with relatively more uniform mortality risks. LEVEL OF EVIDENCE Prognostic study, level II.