Association of Prehospital Blood Product Transfusion During Medical Evacuation of Combat Casualties in Afghanistan With Acute and 30-Day Survival

Abstract

Importance: Prehospital blood product transfusion in trauma care remains controversial due to poor-quality evidence and cost. Sequential expansion of blood transfusion capability after 2012 to deployed military medical evacuation (MEDEVAC) units enabled a concurrent cohort study to focus on the timing as well as the location of the initial transfusion.

Objective: To examine the association of prehospital transfusion and time to initial transfusion with injury survival.

Design, setting, and participants: Retrospective cohort study of US military combat casualties in Afghanistan between April 1, 2012, and August 7, 2015. Eligible patients were rescued alive by MEDEVAC from point of injury with either (1) a traumatic limb amputation at or above the knee or elbow or (2) shock defined as a systolic blood pressure of less than 90 mm Hg or a heart rate greater than 120 beats per minute.

Exposures: Initiation of prehospital transfusion and time from MEDEVAC rescue to first transfusion, regardless of location (ie, prior to or during hospitalization). Transfusion recipients were compared with nonrecipients (unexposed) for whom transfusion was delayed or not given.

Main outcomes and measures: Mortality at 24 hours and 30 days after MEDEVAC rescue were coprimary outcomes. To balance injury severity, nonrecipients of prehospital transfusion were frequency matched to recipients by mechanism of injury, prehospital shock, severity of limb amputation, head injury, and torso hemorrhage. Cox regression was stratified by matched groups and also adjusted for age, injury year, transport team, tourniquet use, and time to MEDEVAC rescue.

Results: Of 502 patients (median age, 25 years [interquartile range, 22 to 29 years]; 98% male), 3 of 55 prehospital transfusion recipients (5%) and 85 of 447 nonrecipients (19%) died within 24 hours of MEDEVAC rescue (between-group difference, -14% [95% CI, -21% to -6%]; P = .01). By day 30, 6 recipients (11%) and 102 nonrecipients (23%) died (between-group difference, -12% [95% CI, -21% to -2%]; P = .04). For the 386 patients without missing covariate data among the 400 patients within the matched groups, the adjusted hazard ratio for mortality associated with prehospital transfusion was 0.26 (95% CI, 0.08 to 0.84, P = .02) over 24 hours (3 deaths among 54 recipients vs 67 deaths among 332 matched nonrecipients) and 0.39 (95% CI, 0.16 to 0.92, P = .03) over 30 days (6 vs 76 deaths, respectively). Time to initial transfusion, regardless of location (prehospital or during hospitalization), was associated with reduced 24-hour mortality only up to 15 minutes after MEDEVAC rescue (median, 36 minutes after injury; adjusted hazard ratio, 0.17 [95% CI, 0.04 to 0.73], P = .02; there were 2 deaths among 62 recipients vs 68 deaths among 324 delayed transfusion recipients or nonrecipients).

Conclusions and relevance: Among medically evacuated US military combat causalities in Afghanistan, blood product transfusion prehospital or within minutes of injury was associated with greater 24-hour and 30-day survival than delayed transfusion or no transfusion. The findings support prehospital transfusion in this setting.

Figure 1.. Study Design

^aHemorrhagic torso injury assessed by Abbreviated Injury Scale (AIS) diagnostic code and severity of head injury assessed by maximum head AIS score.

Figure 2.. Time to Start of First Transfusion Among US Military Combat Casualties Transfused Within 25 Minutes of Rescue

First transfusion started within 25 minutes after medical evacuation (MEDEVAC) rescue for all 55 prehospital transfusion recipients and for 76 nonrecipients who received transfusion during hospitalization. Quartile bounds were determined by the points of intersection on the grid defined by the axes: x (time to the start of transfusion after MEDEVAC rescue in 5-minute increments from 0 to 25) and y (0, 0.25, 0.50, 0.75, 1.00). Time to start for the first transfusion was examined for each quartile relative to longer delays (>25 minutes or no transfusion received within 24 hours after hospital admission).

Figure 3.. Mortality of Prehospital Transfusion Recipients vs Matched Nonrecipients

Adjusted mortality curves were estimated by Cox proportional hazards modeling at the median value of each covariate. The median values for the matching factors were set as follows: (1) 0, explosives for mechanism of injury; (2) 1, yes for documented prehospital shock; (3) 2, two or more traumatic limb amputations below the knee or elbow, or 1 above the knee or elbow; (4) 1, Abbreviated Injury Scale score for head injury of 2; and (5) 1, yes for hemorrhagic torso injuries. The median values for the additional covariates were set as follows: age of 26 years, injury year of 2012, US Army DUSTOFF transport team, yes for prehospital tourniquet, and 29 minutes from injury occurrence to medical evacuation rescue. There were no patients lost to follow-up and the median survival times were 1440 minutes (24 hours) for the 24-hour survival analysis and 30 days for the 30-day survival analysis. HR indicates hazard ratio.

Figure 4.. Mortality by Time From Medical Evacuation (MEDEVAC) Rescue to Start of Transfusion

Adjusted mortality curves by Cox proportional hazards modeling at the median value of each covariate. The median time to start of transfusion was 36 minutes after injury (interquartile range, 27-46 minutes). The median values for the matching factors were set as follows: (1) 0, explosives for mechanism of injury; (2) 1, yes for documented prehospital shock; (3) 2, two or more traumatic limb amputations below the knee or elbow, or 1 above the knee or elbow; (4) 1, Abbreviated Injury Scale score for head injury of 2; and (5) 1, yes for hemorrhagic torso injuries. The median values for the additional covariates were set as follows: age of 26 years, injury year of 2012, US Army DUSTOFF transport team, yes for prehospital tourniquet, and 29 minutes from injury occurrence to medical evacuation rescue. There were no patients lost to follow-up and the median survival times were 1440 minutes (24 hours) for the 24-hour survival analysis and 30 days for the 30-day survival analysis. HR indicates hazard ratio.