Prehospital intervention probability score: a novel method for determining necessity of emergency medical service units☆

Abstract 

Objective

This article models use of emergency medical services (EMS) within a defined geographical area. Our goal was to develop an original quantitative method to delineate the need for EMS units within a geographical population.

Methods

Use of the EMS system within 11 municipalities was analyzed in 2007. The geospatial distributions of interventions during this year were examined, as well as the population dynamics of the region. A statistical model to determine the probability of an individual within the call area requiring an intervention was proposed using weighted population statistics and the application of an intervention probability.

Results

The observed interventional probability increased exponentially with age, notably after the age of 75. Areas with higher proportions of elderly residents had substantially higher rates of intervention and EMS use. Municipality H had the largest age-group of 20 to 24 years with an intervention probability of 0.34% (95% confidence interval [CI], 0.24-0.44), their more than 85-year age-group also had the largest intervention probability of 19.54% (95% CI, 15.60-23.48).

Conclusions

Contrary to current practice patterns of placing paramedic units in regions of greatest population density, we established a formula based on population vs intervention probability. We found the actual numbers of interventions performed are not dependent solely on population size but also are affected by the age of the population being served. This is particularly relevant to growing elderly communities. This determination will aid in the disbursement of limited prehospital resources in regions by improving availability of EMS personnel.