# Barriers to helicopter emergency medical services in a Haze-Prone, mountainous region of Northern Thailand

## TL;DR

This study examines how haze and other factors affect helicopter emergency medical services in northern Thailand, finding that pollution and time of day impact transport success.

## Contribution

The study identifies haze-related air pollution as a novel operational constraint affecting air medical transport in mountainous regions.

## Key findings

- Twilight-hour requests and higher PM2.5 concentrations were independently associated with non-transport outcomes.
- Seasonal haze surges from February to April significantly increased the likelihood of mission failure.
- Primary missions were less likely to be transported compared to secondary missions.

## Abstract

To identify factors associated with the mission outcome (transport completed vs. not transported) of air medical transport (AMT), with particular attention to environmental and operational constraints such as haze-related air pollution.

We conducted a retrospective analysis of all requests to the Northern Thailand Sky Doctor program (SkyDoc) from Jan 1, 2020, to Sept 30, 2024. Patient demographics, mission characteristics, environmental conditions, and operational variables were extracted from program records and merged with daily PM2.5 and PM10 concentrations from the national air quality monitoring network. The primary outcome was mission outcome, defined as transport completed versus not transported. We analyzed factors associated with non-transport.

Among 656 mission requests, 412 (62.8%) were transport and 244 (37.2%) were not transported. Patients were predominantly male (57.2%) with a median age of 49 years (IQR 28–67). The most frequent diagnostic categories were ST-elevation myocardial infarction (32.3%), major trauma (21.2%), and stroke (11.7%). Non-transport was most often due to medical contraindications (25.8%), aircraft or landing-zone unavailability (23.8%), adverse weather (18.9%), and haze-related air pollution (12.7%). Seasonal peaks in not transport were observed from February through April, coinciding with regional surges in particulate matter. In multivariable analysis, twilight-hour requests (16:00–20:00) were associated with non-transport (adjusted OR 0.29; 95% CI 0.13–0.67; p < 0.01), whereas secondary missions were more likely to be transport than primary missions (adjusted OR 3.51; 1.47–8.40; p < 0.01). Higher PM2.5 concentrations were independently associated with non-transport (adjusted OR 0.99; 0.97–0.99; p = 0.018). PM10 was not associated with outcomes.

AMT in northern Thailand is constrained by both medical and environmental factors. Twilight-hour requests, mission type, and PM2.5 concentrations independently influenced mission completion. These findings highlight the need for haze-adapted flight protocols, enhanced forecasting, and system-level strategies to safeguard patient access to aeromedical care during seasonal pollution surges.

The online version contains supplementary material available at 10.1186/s13049-025-01498-w.

Air Medical Transport (AMT) services are essential for timely access to advanced care in remote and mountainous regions. Operational limitations such as weather, geography, and patient condition are recognized barriers, but the impact of environmental air pollution on aeromedical transport has been poorly studied.

In northern Thailand, we found that twilight-hour requests, primary missions, and elevated PM2.5 concentrations were independently associated with air medical non-transport. Seasonal haze surges created critical access barriers during periods of heightened clinical demand.

These findings highlight the need for haze-adapted flight protocols, improved forecasting systems, and policy interventions to strengthen AMT resilience in environments affected by air pollution and complex terrain.

The online version contains supplementary material available at 10.1186/s13049-025-01498-w.