Helicopter Emergency Medical Services attendance is associated with favourable survival outcomes in major trauma: derivation and internal validation of prediction models in a regional trauma system

Background Survival benefit of Helicopter Emergency Medical Services (HEMS) attended major trauma remains inadequately quantified across injury severity. We evaluated HEMS performance and identified predictors of survival. Methods Retrospective observational analysis of 3225 trauma patients attended by a regional HEMS in South-East England (2013–2022). Survival was assessed using W-statistic ( W s ) methodology stratified by probability of survival ( P s ) bands. Multivariable logistic regression identified predictors of 30-day mortality in major trauma (injury severity score (ISS) ≥15). Sub-analysis examined unexpected survival predictors and return of spontaneous circulation (ROSC) rates in traumatic cardiac arrest (TCA). Results Among 2125 patients meeting W s analysis criteria, observed (O) 30-day survival exceeded expected (E) survival (84.7% vs 81.3%; O/E ratio 1.04), yielding adjusted W s of 5.23 (95% CI 3.27 to 7.19), representing 5.23 excess survivors per 100 patients. Survival benefit was greatest in severely injured patients with moderate survival probability ( P s 25–45%: 3.33 excess survivors per 100, 95% CI 1.37 to 5.29). Among patients with low probability of survival ( P s