Ambulance and helicopter response times in emergency medical services. The AHRTEMIS project.

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Response time for emergency medical service (EMS) units such as ambulances, rapid response cars and helicopters is a key performance indicator and is frequently used in the political debate on EMS coverage and performance. Short response time is considered pivotal in critical conditions such as out-of-hospital cardiac arrest and major trauma. Studies have shown reduced response time association with improved outcome, and the opposite has been described as well. Using lights and sirens for rapid EMS response may put conveyed patients, prehospital personnel, and public at potential risk and each year, several serious and fatal accidents occur.

In Scandinavia, the use of criteria-based dispatch is the standard procedure and widely used. The type of EMS response and urgency is decided within the Emergency Medical Dispatch Center by a specialist call-taker, usually a nurse or emergency medical technician. To achieve short response time, EMS vehicles utilize lights and sirens, and crews are allowed to be non-compliant with traffic rules, posing a risk for accidents. Less severe conditions may be managed according to national and international guidelines despite longer response time, suggesting the consideration of additional levels of response beyond the current practice guidelines.

Apart from specific conditions such as out-of-hospital cardiac arrest and trauma, there is lack of scientific evidence, other than best practice, to justify the shortest possible response time is related to improved patient outcomes. Several confounders may affect patient outcomes, including crowding in the receiving hospital and a shortage of personnel. Similarly, prolonged on-scene times as the result of time-consuming complex medical procedures, may affect the time to final treatment in the hospital. Thus, the intention to describe several factors influencing time to an event such as mortality remains paramount.

With the access to a complete database of all ambulance and helicopter missions in Denmark and the unique Danish Civilian Registration Register [18], we have the ability to merge data on response time and data on on-scene time, transport time to a hospital; interventions on the mission; length of hospital stay; days spent in the intensive care unit including ventilator days, SAPS II/III, serious adverse events, and mortality.