Predicting resource needs for multiple and mass casualty events in combat: lessons learned from combat support hospital experience in Operation Iraqi Freedom.

OBJECTIVE We hypothesized that the number of evacuated casualties from a combat-related multiple casualty event provides an initial baseline estimate of the number of blood products required for the event. METHODS A retrospective review of combat support hospitals' experiences in Operation Iraqi Freedom was performed, (from December 2003 to December 2004). Identified multiple casualty events were analyzed for mechanisms of injury, total number of patients arriving to the combat support hospitals, average injury severity score, operative interventions, blood product requirements, and short-term outcomes (24-hour mortality). Selected events in which the Packed cells per Patient Index (PPI) was greater than a SD away from the mean were analyzed further regarding the casualties' injuries, the triage decisions during the event, operations, and patient outcomes. RESULTS Of 367 days and 3,533 casualties, multiple or mass casualty events were identified on 26 days, accounting for 18% of casualties treated for the year. Twenty-two percent of all evacuated casualties from a multiple casualty event required transfusion and 4.2% required massive transfusion. Patients injured by discrete explosion-related events had an increased incidence of massive transfusion compared with patients injured from firefights, 9.6% versus 4%, respectively, (p < 0.05). The average number of RBC units (packed red blood cells units + fresh whole blood units) per patient (PPI) for these events was 1.4 (+/-0.8). Review of casualty events where the PPI was higher revealed either potential triage or treatment errors. CONCLUSION Baseline blood product requirements for a multiple or mass casualty combat-related event can be estimated from the number of evacuated casualties involved.