EMS response time and patient outcomes in high-acuity emergency responses: a Danish matched cohort study

Emergency medical services (EMS) provide prehospital care. To reduce response times, ambulances may use lights, sirens, and traffic exemptions, increasing risks for EMS personnel and other road users. Additionally, predefined response time targets may lead to inefficient resource use. The impact of response times on patient outcomes is unclear. The objective of this study was to assess the association between EMS response times and 30-day mortality as the primary outcome, with 2-day mortality and hospital length of stay (LOS) as secondary outcomes, in a region with small urban centres and extensive rural areas. We conducted a matched cohort study of patients receiving a priority level A response (excluding out-of-hospital cardiac arrests) in Region Zealand, Denmark, from January 2018 to December 2024. Data were linked across registries using civil personal register numbers. Variables included patient demographics, main dispatch category, response times, 30-day and 2-day mortality, and hospital LOS. The patients were stratified into quartiles by response time: the longest quartile (Q4) was compared with the three shortest (Q1-Q3). Groups were matched by sex, age, and highest dispatched resource. A total of 171 708 patients were included in the analyses, all of whom received the highest priority ambulance dispatch. Among these patients, 54.6% were male, with a median age of 63 years (IQR: 41–77). According to Charlson Comorbidity index, 50.7% of the patients had no comorbidities. The most common main dispatch category was “Chest pain, heart disease” accounting for 24.2% of incidents. Response times varied across the region. Mortality did not increase with longer response times, and patients in Q4 had lower 30-day and 2-day mortality than those in Q1-Q3 (OR: 0.87 [95% CI: 0.83–0.91] and OR: 0.82 [95% CI: 0.77–0.87]), respectively. Response times were not associated with hospital LOS. Longer EMS response times were not associated with increased 30-day or 2-day mortality among non-cardiac arrest patients. Mortality was lower in the longest response time quartile, and response time was not associated with hospital LOS. These findings support further evaluation of the criteria used to assign high-acuity EMS responses and the role of predefined response time targets.