Prehospital Blood Transfusions: SWiFT Trial Results Published

Purpose of SWiFT Trial Regarding Prehospital Blood Transfusions

Researchers in the United Kingdom (UK) have shared the results of the Study of Whole Blood in Frontline Trauma (SWiFT) trial in The New England Journal of Medicine. The study took place from December 2022 through September 2024 and sought to, “determine whether prehospital transfusion of up to two units of whole blood was superior to standard blood components in reducing the risk of death or massive transfusion (defined as the administration of ≥10 units of blood components or products) within 24 hours in patients with life-threatening traumatic hemorrhage.” The phase III, multicenter, unblinded, randomized, controlled, superiority trial included 10 air ambulances that serviced 19 hospitals.

The authors of the paper noted that eligible study participants were, “[p]atients of any age with a traumatic injury leading to prehospital transfusion for the treatment of major hemorrhage. Patients were excluded if intravenous or intraosseous access could not be established, if they had a known objection to blood transfusion, or if they had received blood components or products before the arrival of the air ambulance service.” The stated primary outcome was, “a composite of death from any cause or massive transfusion (defined as ≥10 units of any blood components in adults, and ≥40 ml per kilogram of body weight in pediatric participants [<16 years of age with a body weight of <50 kg]) within 24 hours after randomization.”

Findings Regarding SWiFT Trial Prehospital Blood Transfusions

The study included, “data on the primary outcome [for] 616 of the participants (96.1 percent; 314 in the whole-blood group and 302 in the standard-care group). In the adjusted modified intention-to-treat analysis, 48.7 percent of the participants in the whole-blood group and 47.7 percent of those in the standard-care group died or received a massive transfusion within 24 hours after randomization (adjusted relative risk, 1.02; 95 percent confidence interval [CI] 0.80 to 1.31; P=0.84).” Additionally, the researchers found that, “[t]he percentages of participants who had died from any cause at six hours, 24 hours, 30 days, and 90 days after randomization, as well as the percentage of participants who received massive transfusion within 24 hours, appeared to be similar in the two groups. [Slightly] more serious adverse events occurred in the standard-care group (37 events) than in the whole-blood group (31 events).”

Conclusion

The paper concluded that, “[a]mong participants with life-threatening hemorrhage, prehospital transfusion of up to two units of whole blood was not superior to standard transfusion with component therapy in reducing the risk of death or massive transfusion at 24 hours after randomization. The safety profile also appeared to be similar with whole blood and standard care.” The authors noted that the trial, “provides key evidence to inform the use of whole blood within civilian prehospital trauma systems. Decisions about adopting the use of whole blood must balance logistic advantages against supply constraints, cost, and the overall availability of blood.”

Limitations of the study acknowledged in the paper were: “the variability inherent to the prehospital environment and time-critical decision making may have influenced treatment delivery and adherence to the protocol; the pragmatic design, which relied on clinical judgment to initiate transfusion, may have introduced population heterogeneity and led to the inclusion of some patients without life-threatening hemorrhage; the pragmatic trial design was dependent on the routine use of the Trauma Audit and Research Network database for injury characteristics; a cyberattack on this database in 2023 resulted in some missing data.”

Citation: Smith, J.E., Cardigan, R., Sanderson, E., et al. “Prehospital Whole Blood in Traumatic Hemorrhage — a Randomized Controlled Trial.” NEJM. 2026.