The definition of massive transfusion in trauma: a critical variable in examining evidence for resuscitation.

OBJECTIVES: 'Massive' transfusion is a poorly defined inclusion criteria for studies examining the blood and blood product that are used during trauma resuscitation. We aimed to compare the traditional definition of massive transfusion (≥10 units in 24 h) to a more acute definition of at least 5 units in 4 h.
METHODS: Multitrauma patients were subgrouped according to the traditional definition and compared with the acute definition. Demographics, presenting vital signs and blood results, management including transfusion practice and outcomes were retrospectively studied. Associations of transfused fresh frozen plasma:packed red blood cells (PRBC) ratios with mortality were studied.
RESULTS: There were 927 patients who received PRBCs in the first 24 h, with 314 patients identified using the traditional definition and 303 patients using the acute definition. The patients identified using the traditional definition received 18 (12-29) units of PRBC in 24 h, significantly higher than those identified using the acute definition [15 (9-29) units, P<0.001]. The traditional definition excluded a significant proportion of patients who died in the emergency department. By using the acute definition to select a study sample, there seems to be an increase in mortality with fresh frozen plasma:PRBC ratio of 1 : 1 ratio compared with a 1 : 2 ratio.
CONCLUSION: The traditional 'massive' transfusion definition not only 'dilutes' the potential study samples with a less acute group of patients, but also further excludes patients who die early. This latter group is most likely to be benefitted from any change to resuscitation practice. An acute definition of massive transfusion should be adopted when examining clinical practice during initial trauma resuscitation.