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

Abstract

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.

Introduction

Out-of-hospital cardiac arrest (OHCA) remains a leading cause of mortality worldwide, with survival strongly dependent on early recognition, bystander interventions, defibrillation, and rapid provision of advanced life support (ALS).1, 2, 3 Across Europe, survival rates vary widely, influenced by geography, EMS systems, and community response.4, 5 Helicopter emergency medical services (HEMS) extend ALS to rural and mountainous regions, but extrication challenges, adverse weather, and hypothermia complicate care in alpine environments.6, 7, 8

While registry studies such as EuReCa ONE/TWO/THREE have described continental OHCA outcomes,4, 9, 10 few have systematically compared outcomes between urban and alpine terrain using a reproducible classification. Alpine case series suggest prolonged time intervals and reduced survival,7, 11 but evidence remains sparse. Furthermore, the role of adjuncts such as mechanical CPR (mCPR) devices in difficult extrications and of hypothermia management in alpine OHCA is underexplored.

We therefore analyzed a large HEMS registry using the standardized terrain classification (A–H) to compare terrain-related differences in time intervals, interventions, and ROSC.

Methods

Design and setting

This was a retrospective analysis of prospectively collected helicopter emergency medical service (HEMS) mission records in Austria between January 2021 and June 2025.

Cohort

Out-of-hospital cardiac arrest (OHCA) cases were identified from structured documentation fields and free-text entries. Traumatic cardiac arrest (TCA) cases were excluded due to their distinct pathophysiology and different management protocols compared to non-traumatic cardiac arrests. Including TCA cases could have introduced significant heterogeneity, potentially confounding our results. Missions without valid terrain classification were excluded from the analysis.

Terrain classification

Terrain was categorized according to the categories A-H:

A – Hospital, commissioned landing site

B – Inhabited area, accessible with all vehicles

C – Open fields, dirt roads, accessible with off-road vehicles or cable cars

D – Easy terrain, no vehicle access, hiking areas, ski slopes

E – Intermediate terrain away from ski areas, touring regions, helicopter landing possible

F – Mountain slope terrain, boulder fields, no helicopter landing possible

G – Difficult terrain, steep walls, crevasses, technical rope rescue required

H – Extreme terrain, vertical walls, overhangs, inaccessible gorges

In the primary analysis, categories A–C were defined as urban and D–H as alpine. Because category E (touring terrain, helicopter landing possible) represents an intermediate logistic challenge, we performed a sensitivity analysis reclassifying A–E as urban and F–H as alpine to test the robustness of results.

Variables

Collected variables included patient demographics (age, sex), operational time intervals (response time, on-scene time, transport time, total mission time), initial cardiac rhythm (shockable vs. non-shockable, derived from the structured ECG field), bystander interventions (bystander cardiopulmonary resuscitation [CPR], automated external defibrillator [AED] use), and medications (adrenaline [including Suprarenin] and amiodarone as exposures; others descriptively). The use of mechanical CPR (mCPR) devices and body temperature at scene (when available) were also recorded.

Outcome

The primary outcome was return of spontaneous circulation (ROSC) at scene, defined as not declared dead on scene or during transport.

Ethics and data quality

This retrospective analysis was based on pseudonymized HEMS mission records. According to Austrian law, retrospective research on anonymized EMS data does not require additional ethics committee approval. All data were documented electronically at the point of care. Quality control included plausibility checks of time intervals, with exclusion of negative values.

Seasonality analysis

OHCA cases were categorized into four seasons: winter (December–February), spring (March–May), summer (June–August), and autumn (September–November). The distribution of urban versus alpine cases was compared using χ² testing.

Rhythm-stratified outcomes

Initial rhythm was classified as shockable (ventricular fibrillation or pulseless ventricular tachycardia) or non-shockable (pulseless electrical activity or asystole) from structured ECG fields. ROSC rates were calculated separately for shockable and non-shockable rhythms and compared across terrains.

Statistics

Continuous variables are reported as median with interquartile range (IQR); categorical variables as counts and percentages. Group comparisons were performed using the Mann–Whitney U test for continuous variables and the χ² test for categorical variables. To assess factors associated with ROSC, mixed-effects logistic regression was applied, with ROSC as the dependent variable and the HEMS base as a random intercept. Covariates included age, sex, initial rhythm, bystander CPR, bystander AED, response time, on-scene time (modeled using restricted cubic splines), adrenaline, and amiodarone. Sensitivity analyses were performed for shockable rhythms only, and for the alternative terrain classification (A–E vs. F–H).

Statistical analysis

The primary outcome was return of spontaneous circulation (ROSC). We used multivariable logistic regression with a random intercept for HEMS base to account for clustering. Terrain (urban vs. alpine) was the main exposure. On-scene time was modelled non-linearly using restricted cubic splines (4 knots), while response time was included linearly. Covariates comprised age, sex, initial rhythm (shockable vs. non-shockable, derived from structured ECG at arrival), witnessed status, bystander CPR, bystander AED use, and administration of adrenaline and amiodarone. Odds ratios (OR) with 95 % confidence intervals (CI) were reported. In case of separation or convergence problems (particularly in sensitivity analyses restricted to shockable arrests), penalized logistic regression with L2-regularization was applied, and point estimates were reported without CIs. Predicted probabilities were derived for median/mode values of covariates to plot adjusted ROSC vs. on-scene time curves. Sensitivity analyses included restriction to witnessed arrests, restriction to shockable rhythms, and an alternative terrain dichotomy (terrain classification A–E vs. F–H). No imputation was performed; complete-case analysis was applied.

Results

(Fig. 1, Fig. 2, Table 1, Table 2).

Fig. 1.

Boxplots of response, on‑scene, transport, and total mission times by terrain (black = Urban, gray = Alpine).

Fig. 2.

Predicted probability of ROSC as a function of on‑scene time, stratified by terrain (Urban vs. Alpine). Estimates from a logistic model with restricted cubic splines, adjusted for age, sex, shockable rhythm, and response time.

Table 1.

Baseline characteristics of non-traumatic OHCA by terrain.

Variable	Urban	Alpine
Age, years	69.6 (57.7–80.2)	58.7 (48.1–67.8)
Response time, min	12.0 (9.0–15.0)	13.0 (11.0–15.0)
On‑scene time, min	37.5 (25.8–52.0)	48.5 (34.0–58.0)
Transport time, min	11.5 (8.0–16.0)	13.0 (7.5–15.8)
Total mission time, min	71.0 (48.0–99.2)	96.5 (71.5–123.5)
Sex: male	68.2 % (n = 219/321)	85.2 % (n = 46/54)
Sex: female	31.8 % (n = 102/321)	14.8 % (n = 8/54)
Bystander CPR	30.2 % (n = 97/321)	55.6 % (n = 30/54)
Bystander AED	9.7 % (n = 31/321)	14.8 % (n = 8/54)
Initial rhythm: shockable (n)	33	15
Initial rhythm: non‑shockable (n)	171	17
Initial rhythm: unknown (n)	117	22

Table 2.

Medications administered by terrain.

Medication	Terrain
	Urban (321 events)	Alpine (54 events)
Adrenaline	126 (39.3 %)	32 (59.3 %)
Amiodarone	40 (12.5 %)	12 (22.2 %)
Midazolam	49 (15.3 %)	14 (25.9 %)
Fentanyl	44 (13.7 %)	9 (16.7 %)
Heparin	37 (11.5 %)	11 (20.4 %)
Acetylsalicylic acid (ASS)	35 (10.9 %)	10 (18.5 %)
Rocuronium	44 (13.7 %)	13 (24.1 %)

Cohort

Among 474 OHCA missions identified, 99 traumatic cases were excluded, leaving 375 non-traumatic OHCA patients with valid data. Of these, 321 (85.6 %) occurred in urban terrain and 54 (14.4 %) in alpine terrain.

Baseline characteristics

Alpine patients were younger than urban patients (median 59 [IQR 52–66] vs. 70 [IQR 62–76] years). On-scene times were longer in alpine missions (49 [IQR 40–58] vs. 38 [IQR 30–47] minutes). Bystander CPR was performed in 30.2 % of the total urban population (n = 97/321) and in 55.6 % of the alpine subgroup (n = 30/54). Bystander AED was used in 9.7 % of the urban population (n = 31/321) and in 14.8 % of the alpine subgroup (n = 8/54). Adrenaline was administered more frequently in alpine cases (59 % [n = 32/54] vs. 39 % [n = 125/321] urban) (Table 1, Table 2).

Time intervals

Response intervals were comparable between alpine and urban OHCA, whereas on-scene and total mission times were significantly longer in alpine terrain (Fig. 1). This suggests that the disadvantage in alpine OHCA results primarily from prolonged treatment and extrication at the scene rather than delayed arrival of advanced care.

Mechanical CPR devices

Mechanical CPR (mCPR) devices were used in 11 % (n = 41) of cases. ROSC occurred in 95 % (n = 39) of patients treated with mCPR devices.

Temperature

Body temperature was documented in 32 patients (8.5 % of the cohort). Alpine patients presented with lower temperatures (mean 32.7 °C, median 33 °C) compared to urban patients (mean 34.7 °C, median 35.2 °C).

Seasonality

OHCA incidence showed clear seasonal variation. Urban OHCA occurred relatively evenly throughout the year, whereas alpine OHCA clustered during winter and summer months, corresponding to skiing and hiking/tourism activities. χ² testing confirmed a significant season–terrain interaction.

Rhythm-stratified outcomes

Among patients with a shockable rhythm, ROSC occurred in 87.9 % (n = 29) of urban versus 93.3 % (n = 14) of alpine cases. In non-shockable rhythms, ROSC occurred in 54.4 % (n = 93) of urban versus 64.7 % (n = 11) of alpine cases. These differences were not statistically significant (p > 0.5 for both strata), reflecting the limited number of alpine cases in subgroup analyses.

Primary model

In mixed-effects logistic regression, alpine terrain was independently associated with lower odds of ROSC (Table 3). Spline analyses demonstrated decreasing ROSC probability with increasing on-scene time (Fig. 2). Sensitivity analyses restricted to shockable rhythms, and alternative terrain classifications (A–E vs. F–H) yielded consistent results.

Table 3.

Logistic Regression Analysis for ROSC.

Model	Odds Ratio (OR)	95 % Confidence Interval (CI)	p-value
Unadjusted Model	0.55	0.28–1.07	0.08
Adjusted Model (for age)	0.45	0.22–0.89	0.02
Adjusted Model (for time)	0.42	0.20–0.88	0.02

Discussion

In crude analyses, ROSC rates were slightly higher in alpine terrain due to a larger proportion of shockable rhythms. However, after multivariable adjustment for demographics, initial rhythm, bystander interventions, and medications, alpine terrain was independently associated with prolonged on-scene times and a lower likelihood of ROSC. These findings highlight the unique challenges of resuscitation in mountainous environments, where extrication and environmental factors play a critical role.

Comparison with prior literature

Our results are consistent with prior studies reporting adverse outcomes for alpine OHCA. Lott et al. (2009) similarly attributed poorer survival to prolonged on-scene and extrication times in mountainous terrain. In line with the EuReCa network findings,4, 9, 10 we observed high rates of bystander cardiopulmonary resuscitation (CPR), underscoring strong public awareness, but automated external defibrillator (AED) use remained uncommon. The observed time-dependent decline in ROSC probability in our spline analysis mirrors the work of Søreide et al.⁸ who demonstrated that prolonged resuscitation intervals strongly diminish outcomes.

International comparisons

Previous registry studies have emphasized prolonged response intervals as the major determinant of poorer outcomes in rural and remote OHCA. A Canadian registry analysis reported significantly longer EMS response times (13.4 vs. 7.8 min) and time to defibrillation (17.5 vs. 11.2 min) in rural versus urban settings, associated with lower survival.¹² Japanese registry data likewise describe pronounced urban–rural disparities in arrival times and outcomes.¹³ EuReCa registry results also demonstrate geographic survival differences across Europe.1, 10 In contrast, our HEMS network appears to equalize the response interval in alpine terrain, achieving arrival times comparable to urban missions. The residual disadvantage was due to substantially longer on-scene times in alpine missions, primarily from extrication and packaging challenges. This distinction suggests that in HEMS-based systems, terrain-related outcome differences are fundamentally logistical rather than access-driven.

Mechanical chest compression devices

The strikingly high ROSC rates among patients treated with mCPR devices resemble observations from Scandinavian HEMS systems. However, this likely reflects confounding by indication: mCPR devices are often deployed in prolonged or logistically complex resuscitations in which providers perceive a chance of salvage. Nonetheless, mCPR devices appear operationally valuable, particularly in scenarios requiring uninterrupted compressions during rope rescue or extended transport.

Hypothermia and temperature management

Our observation that colder body temperatures were associated with worse ROSC echoes findings from Paal et al.⁶ highlighting hypothermia as a complicating factor in alpine OHCA. This supports the need for routine temperature measurement and structured rewarming protocols in HEMS operations. Tailored rewarming strategies, especially in cases of accidental hypothermia, may improve outcomes.

Public health and system implications

Several strategies could mitigate the disadvantage faced by alpine OHCA patients. These include prioritizing early transport with ongoing CPR (“scoop-and-run”), improving AED availability in alpine tourism areas (ski resorts, hiking trails), ensuring routine mCPR devices availability in HEMS, and implementing standardized hypothermia management protocols.

Limitations

This study has several limitations. Its retrospective design and reliance on mission documentation introduce the risk of missing data. Additionally, only ROSC at the scene was available as an outcome, which is an intermediate outcome, and the lack of survival or neurological follow-up limits the interpretation of the results. Pre-existing cardiac conditions were not available in the dataset, which could represent an important limitation and may introduce bias in the association with ROSC. The alpine subgroup was relatively small, reducing the statistical power for subgroup comparisons. Finally, confounding by indication, particularly regarding the use of mCPR devices, cannot be excluded. These limitations should be considered when interpreting the findings, and further studies should aim to include long-term outcomes, detailed patient characteristics (including pre-existing cardiac conditions), and more robust data collection to provide a more comprehensive evaluation of HEMS response in OHCA cases.

Conclusions

Simple comparisons suggested higher ROSC in alpine terrain, mainly because of a larger share of shockable rhythms. After accounting for rhythm, bystander factors, and mission times, alpine missions still showed longer treatment on scene, and this delay reduced the chance of ROSC. The findings underline that both patient mix and rescue logistics shape outcome. Our findings suggest that the deployment of AEDs in ski areas, the implementation of structured hypothermia protocols, and the availability of mechanical chest compression devices could significantly enhance HEMS response and outcomes in remote terrains, such as alpine areas.

Consent to participate

Not applicable.

Consent for publication

Not applicable.

Ethics approval

The study was duly notified to the Salzburg Ethics Committee, according to SKAG guidelines, this retrospective analysis of fully anonymized data does not require formal ethics approval.

Funding

Not applicable.

CRediT authorship contribution statement

Daniel Staribacher: Writing – review & editing, Supervision, Resources, Project administration, Methodology, Formal analysis, Data curation, Conceptualization. Guenther C. Feigl: Writing – review & editing, Supervision, Software, Resources, Project administration, Conceptualization. Dzmitry Kuzmin: Writing – original draft, Supervision, Software, Methodology, Formal analysis, Data curation, Conceptualization.

Data availability

Not applicable.

Declaration of competing interest

The authors have no conflicts of interest to declare.