Impact of Helicopter Emergency Medical Services on endovascular thrombectomy delays, clinical outcomes, and societal costs in large vessel occlusion stroke: a retrospective registry based counterfactual simulation study

Background The efficacy of endovascular thrombectomy (EVT) for large vessel occlusion (LVO) stroke is highly time-dependent. This study evaluates the logistical, clinical, and economic utility of physician-staffed Helicopter Emergency Medical Services (HEMS) within a centralized stroke network. Methods This retrospective study (2021–2025) of 617 EVT-treated LVO patients used spatial simulations on a 159-patient subset, excluding those with missing data, non-transport delays, and distances ≤ 30 km. Simulation 1 compared 42 realized HEMS missions to simulated ground transports across varying on-scene times (OST). Simulation 2 modeled 117 ground-transported patients (> 30 km) as hypothetical HEMS missions under simultaneous vs. secondary dispatch protocols. Clinical and economic impacts were estimated using ordinal logistic regression, HERMES meta-analysis estimates, and a 2-year societal cost model. Results HEMS patients had higher baseline severity (median NIHSS 19 vs. 14, p < 0.001). Multivariable regression confirmed EVT delay independently predicted a 90-day mRS shift. In Simulation 1, a “scene-time paradox” was identified: prolonged on-scene stabilization negated the aerial transit advantage, with the Rapid-Extrication Scenario showing a modest 1.7-minute HEMS saving whereas the Matched-OST Scenario isolating pure transit speed yielded a 19.7-minute advantage. In Simulation 2, simultaneous HEMS dispatch saved a median of 4.8 min for patients located > 30 km away, with over 31% saving > 20 min. Conversely, secondary dispatch caused a median time loss of 3.8 min. Implementing an optimized simultaneous dispatch protocol could prevent 0.76 to 1.98 cases of severe disability over the 5-year period, equating to 2-year societal savings of €39,000 to €107,000 (annualized ~€7,800 to €21,400 per operational year). Conclusions While HEMS provides a transit advantage for LVO stroke, its utility is heavily influenced by on-scene critical care requirements and dispatch timing. Because secondary dispatch negates aerial speed advantages, simultaneous dispatch is essential for maximizing both clinical and economic benefits.