INTRODUCTION

Response time for emergency medical service vehicles, such as ambulances and helicopters, is commonly used as a key performance indicator in emergency medical service systems. Short response times are crucial in time-sensitive emergencies, including out-of-hospital cardiac arrest and severe trauma. However, the use of lights and sirens and high driving speeds can pose significant risks to patients and personnel and may compromise public safety. Every year, numerous serious and fatal ambulance-related accidents occur worldwide. In Scandinavia, the decision to use lights and sirens when responding to an emergency is guided by a criteria-based dispatch tool operated by the Emergency Medical Dispatch Center.

                                    PERSPECTIVE AND PURPOSE

The AHRTEMIS project aims to strengthen knowledge and understanding in the field of criteria-based dispatch and to provide decision-makers with the possibility of applying a more differentiated assessment of response urgency for optimal resource utilization. To achieve this, a Ph.D. thesis consisting of three studies and one protocol article was planned, combining a systematic review and meta-analysis with two observational studies on ambulance and helicopter response times, and their association with mortality and advanced intensive care unit treatment characteristics, including mechanical ventilation, use of vasopressors and dialysis. Based on the findings of the AHRTEMIS project, the aim is to propose a differentiated response model. 

The Ph.D. thesis was submitted to the University of Southern Denmark on 31 July 2026. The thesis defense will be announced once the thesis has been evaluated by the assessment committee.

PROJECT GROUP

Peter Martin Hansen, MD, M.Sc., Ph.d. student, Consultant. The Prehospital Research Unit, Region of Southern Denmark, Odense University Hospital, Denmark, Danish Air Ambulance, Aarhus, Denmark, Department of Regional Health Research, University of Southern Denmark, Odense, Denmark. Ph.D. student.

Søren Mikkelsen, MD, Ph.D., Consultant, Professor, The Prehospital Research Unit, Region of Southern Denmark, Odense University Hospital, Denmark, Department of Regional Health Research, University of Southern Denmark, Odense, Denmark. Main supervisor.

Marius Rehn, MD, Ph.D., Consultant, Professor, Oslo University Hospital, The Norwegian Air Ambulance Foundation, Oslo, Norway, Department of Regional Health Research, University of Southern Denmark, Odense, Denmark. Co-supervisor.

Anders Perner, MD, Ph.D., Consultant, Professor, Rigshospitalet, Copenhagen, Denmark. Co-supervisor.

Annmarie Touborg Lassen, MD, Ph.D., DMA, Consultant, Professor, Head of Research, Emergency Medicine Research Unit, Odense University Hospital, .Department of Clinical Medicine, University of Southern Denmark, Odense, Denmark.  Co-supervisor.

Anne Craveiro Brøchner, MD, Ph.D., Consultant, Associate Professor, The Prehospital research Unit, Region of South Denmark, Kolding University Hospital, Denmark, Department of Regional Health Research, University of Southern Denmark, Odense, Denmark. Co-worker.

Helle Collatz Christensen, MD, Ph.D., Consultant, Professor, Prehospital Services, Prehospital Center, Region Zealand, Næstved, University of Copenhagen. Co-worker.

Stig Nikolaj Blomberg, Ph.D., Prehospital Services, Prehospital Center, Region Zealand, Næstved. Co-worker.

BACKGROUND

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 political discussions about EMS coverage and performance. Short response time is considered crucial in time-critical conditions such as out-of-hospital cardiac arrest and major trauma. Studies have demonstrated an association between reduced response time and improved outcomes, while the opposite has also been reported. However, using lights and sirens to achieve rapid EMS response may expose transported patients, prehospital personnel, and the public to potential risk, and each year several serious and fatal accidents occur.

In Scandinavia, criteria-based dispatch is the standard and widely used procedure. The type and urgency of EMS response are determined at the Emergency Medical Dispatch Center by a specialist call-taker, usually a nurse or emergency medical technician. To achieve short response times, EMS vehicles use lights and sirens, and crews are permitted to deviate from traffic regulations, thereby increasing the risk of accidents. Less severe conditions can often be managed according to national and international guidelines despite longer response times, indicating that additional levels of response beyond current practice guidelines may be appropriate.

Apart from specific conditions such as out-of-hospital cardiac arrest and major trauma, there is limited scientific evidence to support that the shortest possible response time is consistently associated with improved patient outcomes. Several confounders may influence patient outcomes, including age, sex, demographic characteristics, and comorbidity. Likewise, prolonged on-scene times due to time-consuming and complex medical procedures may delay definitive treatment in the hospital. Therefore, describing and understanding the multiple factors that influence mortality remains essential.

With access to a comprehensive database of all ambulance and helicopter missions in Denmark and the unique Danish Civil Registration Register, it is possible to link response time time with in-hospital with data on interventions, length of hospital stay, days in the intensive care unit including ventilator days, dialysis, vasopressor use, and mortality. These data can be merged with several high-quality national registries containing information on patient demographics and other relevant characteristics, providing a robust foundation for addressing the research question.