Drivers of Increasing Emergency Ambulance Demand.

Abstract
Objectives: Although the factors driving emergency department demand have been extensively investigated, a comparatively minimal amount is known about the factors that are driving an increase in emergency ambulance demand.
Methods: We conducted a retrospective observational study of consecutive cases attended by Ambulance Victoria in Melbourne, Australia from 2008 to 2015. Incidence rates were calculated, and adjusted time series regression analyses were performed to assess the driving factors of ambulance demand.
Results: A total of 2,443,952 consecutive cases were included. Demand grew by 29.2% over the 8-year period. The age-specific incidence increased significantly over time for patients aged < 60 years, but not for patients aged ≥ 60 years. After adjustment for seasonality and population growth, demand increased by 1.4% per annum (incident rate ratio [IRR] = 1.014 [1.011-1.017]). The largest annual growth in demand was observed in patients with a history of mental health issues (IRR = 1.058 [1.054-1.062]), alcohol/drug abuse (IRR = 1.061 [1.056-1.066]), or a Charlson Comorbidity Index [CCI] score ≥ 4 (IRR = 1.045 [1.039-1.051]). Cases involving patients of relative socio-economic/educational disadvantage, younger age, or with no preexisting health conditions according to the CCI also grew faster than the overall patient population. Cases requiring transport to hospital increased by 1.2% annually (IRR = 1.012 [1.009-1.016]), although patients not requiring medical intervention from paramedics increased by 6.7% annually (IRR = 1.067 [1.063-1.072]). Conclusions: Increases in ambulance demand exceeded population growth. Emergency ambulances were increasingly utilized for transport of patients who did not require medical intervention from paramedics. Identifying the characteristics of patients driving ambulance demand will enable targeted demand management strategies.