Case-control analysis of prehospital death and prolonged field care survival during recent US military combat operations

BACKGROUND: Quantification of medical interventions administered during prolonged field care (PFC) is necessary to inform training and planning. MATERIALS AND METHODS: Retrospective cohort study of Department of Defense Trauma Registry casualties with maximum Abbreviated Injury Scale (MAIS) score of 2 or greater and prehospital records during combat operations 2007 to 2015; US military nonsurvivors were linked to Armed Forces Medical Examiner System data. Medical interventions administered to survivors of 4 hours to 72 hours of PFC and nonsurvivors who died prehospital were compared by frequency-matching on mechanism (explosive, firearm, other), injury type (penetrating, blunt) and injured body regions with MAIS score of 3 or greater. Covariates for adjustment included age, sex, military Service, shock, Glasgow Coma Scale, transport team, MAIS and Injury Severity Score (ISS). Sensitivity analysis focused on US military subgroup with AIS/ISS assigned to nonsurvivors after autopsy. RESULTS: The total inception cohort included 16,202 casualties (5,269 US military, 10,809 non-US military), 64% Afghanistan, 36% Iraq. Of US military, 734 deaths occurred within 30 days, nearly 90% occurred within 4 hours of injury. There were 3,222 casualties (1,111 US military, 2,111 non-US military) documented for prehospital care and died prehospital (691) or survived 4 hours to 72 hours of PFC (2,531). Twenty-five percent (815/3,222) received advanced airway, 18% (583) ventilatory support, 9% (281) tourniquet. Twenty-three percent (725) received blood transfusions within 24 hours. Of the matched cohort (1,233 survivors, 490 nonsurvivors), differences were observed in care (survivors received more warming, intravenous fluids, sedation, mechanical ventilation, narcotics, antibiotics; nonsurvivors received more intubations, tourniquets, intraosseous fluids, cardiopulmonary resuscitation). Sensitivity analysis focused on US military (732 survivors, 379 nonsurvivors) showed no significant differences in prehospital interventions. Without autopsy information, the ISS of nonsurvivors significantly underestimated injury severity. CONCLUSION: Tourniquets, blood transfusion, airway, and ventilatory support are frequently required interventions for the seriously injured. Prolonged field care should direct resources, technology, and training to field technology for sustained resuscitation, airway, and breathing support in the austere environment. LEVEL OF EVIDENCE: Prognostic, Level III.