Defining a mission-based method to determine a HEMS unit’s actual service area

Abstract

Background Geographical service areas are used as descriptive system indicators in Emergency Medical Service (EMS) related studies and reporting templates. The actual service area may differ significantly from administrative areas; this may lead to inaccuracy in determining indicator values, such as population or mission density, thus making it biased when comparing results between different areas and organizations. The aim of this study was to introduce a univocal, repeatable and easily adaptable method to determine the actual service area of a helicopter emergency medical service (HEMS) unit for statistical, quality measurement and research purposes using widely available geographical information (GIS) and statistical analysis tools. Methods The method was first tested with Tampere HEMS unit. All accepted missions in 2017 were extracted from FinnHEMS database (FHDB). We calculated distance from HEMS base to each accepted mission location. Missions were reordered based on the distance and 99th and 95th percentiles were calculated for mission distances. Convex hulls including 100, 99 and 95% of the missions, and the population and area covered by these missions, were then calculated. The method was repeated for all Finnish HEMS bases. Results Approximately 90% of Tampere HEMS unit’s accepted missions took place within 100 km from the base. 10.9% of the missions occurred outside of the administrative service area. 95% convex hull areas are most in line with the everyday experience of where the units actually operate. In Tampere, the 95% convex hull area corresponds to 76,5% of the administrative area’s population and to 89,8% of its area. Calculating the 95% convex hull areas for all Finnish HEMS units results in service areas that overlap at some points, and some areas of the country fall outside of all HEMS service areas. Conclusions Administrative areas do not correspond to the actual service areas of HEMS units. The service area of a HEMS unit defined by administrative boundaries may differ significantly from actual operations. Using historical mission data to create a convex hull that incorporates mission locations could offer a standardized and comparable solution for determining actual HEMS unit service areas, which can be used for statistical comparison, quality measurement and system development.

The first seven years of nationally organized helicopter emergency medical services in Finland – the data from quality registry

“…Five HEMS units are based at the university hospitals and one in Lapland, and their actual service areas encompassing 95% of the operations cover nearly the whole population of Finland (Fig. 1) [16,17]. The three southernmost units operate with Airbus H135 and the three other units with Airbus H145 helicopters.…”

“…Over the years there have been minor revisions in the datasets, presented in Additional File 3. FHDB is used for daily reporting, scientific purposes and the governing of HEMS operations as a whole [16,[18][19][20]. The database also allows the creation of specific casereport forms for research projects or to monitor effects of specific quality improvement interventions.…”

“…Response time from alarm to patient contact was available for all missions where the patient was encountered, and the median was 19 min (Q1/Q3 14/30 min, Fig. 1 The population density of Finland, location of HEMS bases and their actual service areas with 95% of the missions in 2017 [16,17]…”

“…The database contains only a subset of all EMS patients and dispatching criteria in our system might omit patient groups prominent in other systems. Despite these limitations, FHDB stores a large amount of nationwide data that can be, and already has been, used for further research in prehospital EMS and HEMS [16,18,19]. The data is being combined with the national discharge register and mortality data, enabling studies assessing survival, factors associated with changes in mortality and length of hospitalization.…”

Factors affecting development of air ambulance base: A systematic review and thematic analysis

“…In this study, 90% of the missions occurred in distance of 100 km from air ambulance bases and only 10.9% of the missions had been occurring in longer distances. [ 16 ] In Iran also, distance of 150 km is an important factor in locating the bases for coverage of byroads, paths, mountains, and villages. [ 38 ]…”