Out-of-hospital cardiac arrest in alpine and urban terrain: a five-year retrospective analysis of 11,315 Austrian HEMS missions.

Background: Out-of-hospital cardiac arrest (OHCA) in alpine terrain poses unique problems: extrication often takes longer, patients are exposed to cold, and transport can be difficult. Helicopter emergency medical services (HEMS) shorten access times, but the impact of terrain on prehospital care and outcomes is not well defined. Methods: We reviewed 11,315 HEMS missions in Austria from 2021 to 2025. Non-traumatic OHCA was identified; trauma cases were excluded. Terrain was coded by a standardized classification (A-C = urban; D-H = alpine). The main endpoint was return of spontaneous circulation (ROSC). We compared time intervals, bystander measures, drug administration, and device use. Mixed-effects logistic regression (clustered by base) was used to examine the association of terrain with ROSC, adjusting for age, sex, initial rhythm, bystander CPR/AED, response and on-scene times, and adrenaline/amiodarone. Results: Among 375 non-traumatic OHCA cases, 321 occurred in urban terrain and 54 in alpine terrain. Patients in alpine missions were younger (median 59 vs. 70 years) and their treatment at scene lasted longer (median 49 vs. 38 min). Crude ROSC was actually higher in alpine terrain (70.4 % vs. 63.6 %), largely because more patients presented with shockable rhythms. After adjustment, however, alpine terrain was linked to longer on-scene care and a lower likelihood of ROSC. Bystander CPR was frequent (>60 %), AED use rare (<10 %). Adrenaline was given more often in alpine cases (59 % vs. 39 %). Mechanical CPR (mCPR) devices were used in 11 % overall, with higher use in alpine terrain. ROSC was observed in 95 % of patients with mCPR devices, though this likely reflects case selection. Body temperature data were limited, but lower values in alpine cases appeared to reduce ROSC rates. It is important to note that ROSC is an intermediate outcome, and survival-to-discharge or neurological outcomes were not included. Conclusion: ROSC was somewhat more common in alpine cases at first glance, reflecting case mix. Yet once rhythm and other factors were considered, alpine missions required more time on scene and this delay translated into lower odds of ROSC. Terrain-specific strategies-routine mCPR devices access, structured hypothermia management, and improved logistics-are needed to improve outcomes in these settings.