Ambulance and helicopter response time. Association with patient outcome and illness severity: Protocol of a systematic literature review and meta‐analysis

Response time for emergency medical service units is a key performance indicator. Studies have shown reduced response time association with improved outcome for specific critical conditions. To achieve short response time, emergency vehicles utilize lights and sirens, and crews are allowed to be non‐compliant with traffic rules, posing a risk for accident.

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.[11][12][13] In Scandinavia, the use of criteria-based dispatch 14,15 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, 16 posing a risk for accident.However, less severe conditions could 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, 1,2 there is lack of scientific evidence, other than best practice, to justify the shortest possible response time is related to improved patient outcomes. 8Several 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.

| Objectives
The purpose of the systematic review and meta-analysis is to provide an overview of the current body of evidence regarding the association, if any, between ambulance and helicopter response time and major complications and mortality in patients conveyed by ambulance and/or helicopter.Our secondary aim will be to enhance knowledge in the field of criteria-based dispatch in EMS to provide decision makers with evidence to optimize EMS dispatch.

| Research questions
• What is the association between overall emergency medical services (EMS) unit response time and patient outcomes, major complications, and time-critical conditions?
• What is the internal and external validity of the included literature?

| METHODS
We plan the systematic review and meta-analysis to be in accordance with the Cochrane Handbook 17 and Joanna Briggs Institute Manual for Systematic Reviews. 18The protocol for the systematic review and metaanalysis adheres to the Preferred Reporting Items for Systematic Review and Meta-analysis (PRISMA) PRISMA-P 2015 statement for protocols 19 and the PRISMA-P 2015: Elaboration and Explanation document 20 (see Table 1).We have developed the search strategy with the assistance of a research librarian.Following the systematic removal of duplicates according to guidelines, two members of the project group will screen titles and abstracts for data extraction.Subsequently, a full-text review will be performed using the Covidence ®21 software.Quality appraisal will provide a detailed overview of scientific quality, possible biases, internal and external validity, and reproducibility of the included papers.We have registered the systematic review with the International Prospective Register of Systematic Reviews, PROSPERO 22 on 10 September 2023 (acknowledgement of receipt [462339], DOI pending) to comply with the PRISMA 23 guidelines for reporting systematic reviews.

| Eligibility criteria
Every study design is eligible, including qualitative, quantitative, and mixed-methods designs.
We will include all articles in English, Scandinavian, German, French and Portuguese in this systematic review.For potentially eligible articles in other languages with an English abstract, we will use Google Translate in the screening.
The methodology will include formulating the review questions using a Population, Exposure, and Outcome (PEO) framework. 24

| Population
Studies examining ambulance and helicopter response in EMS will be included.We will include literature describing all kinds of civilian ambulance, rapid response car and helicopter missions performed with high acuity.Studies describing patients with the need for ambulance or helicopter delivered care in the prehospital environment will be included.

| Exposure
Exposure is transport by ambulance and/or helicopter with recorded response/activation time if warranted.

| Outcome
Primary outcome will be: • Association between ambulance and helicopter response times and patient outcome (as per defined in the study) Association with mortality, for example, 24-h survival, 30-day survival.
Secondary outcomes will be: • What is the scientific evidence of a possible association between ambulance and helicopter response times and illness severity and on-scene interventions?
Association with days spent in hospital, advanced specialist treatment, and validated outcome measures, such as the modified Rankin Scale, Glasgow Outcome Scale, Extended Glasgow Outcome Scale, health-related quality of life, Cerebral Performance Category, Overall Performance Category, if applicable.

| Information sources
We will search the following databases: • MEDLINE (Ovid) • Cochrane library (Wiley) • EMBASE (Ovid) • CINAHL (EBSCO) • Clinical trial registries We will not impose time limits to avoid missing relevant literature.Furthermore, we will do forward and backward citation searches on included studies and report the search in accordance with the PRISMA extension for searching. 25To avoid missing relevant literature, we will scan reference lists of the included literature for additional publications, relevant to the review.We will include non-indexed and grey literature and search the following databases: • Web of Science https://oatd.org/.See Additional material S1 for search strategy and example of a search.
To avoid the duplication of evidence, we have performed a preliminary search of relevant databases such as PROSPERO, PubMed/ MEDLINE, CINAHL, the Cochrane database and Embase.We found no current or ongoing scoping or systematic reviews concerning ambulance and helicopter response times.Therefore, after a more exhaustive search, we believe a systematic or scoping review of the available evidence in the area has not been published nor is considered for publication at this time.

| Data management
After the literature search, we will upload every identified study in EndNote20 ® (Alfasoft AB, Gothenburg, Sweden) 27 software for duplicate removal if warranted.Subsequently, we will upload in Covidence ® (Veritas Health Innovation, Melbourne, Australia) 21 software to secure complete duplicate removal.

| Selection process
Two independent reviewers (PMH and MSN) will screen titles and abstracts for relevance.We will assess any potentially relevant study for inclusion in detail after retrieval, that is, full text review.A third reviewer (ACB) will resolve any disagreements between primary reviewers at each stage of the selection process.We will report the results of the search In the PRISMA flow diagram in the final systematic review.

| Data collection process
From a predefined data extraction instrument (Table 2 and Additional material S2), validated from known references 28, 29 and used in similar studies, two review authors (PMH and MSN) will independently extract specific, predefined details about the population, exposure, outcomes framework and key findings with relevance to the review outcomes as per research questions.We will enter data extraction variables into a template for an overview.We will address the authors of relevant studies to retrieve additional information if warranted.

| Data items
From the predefined data extraction instrument (Table 2), we will extract the PEO items including patient outcome characteristics such as 24-h and 30-day survival, days spent in hospital, advanced specialist treatment, validated outcome measures, if applicable, data on geopolitical setting, EMS characteristics, EMS response characteristics, Ambulance and helicopter activation characteristics, Ambulance and helicopter response times characteristics.
In the event of missing or unclear information, we will state that in the data extraction template.If the information is deemed critical, we will contact the authors.We will not make assumptions regarding the interpretation of the results of the included literature.

| Outcomes and prioritization
Primary outcomes: The primary outcome will be response time association with mortality, if applicable.
Secondary outcomes: 1. Response time association with days spent in hospital; advanced specialist treatment; validated outcome measures (e.g., modified Rankin Scale, Glasgow Outcome, Scale, Extended Glasgow Outcome Scale, health-related quality of life, Cerebral Performance Category, Overall Performance Category)

| Risk of bias in individual studies
We will assess the quality and risk of bias in the included literature from a predefined quality assessment instrument (Table 3 and Additional material S3), validated from known references 28, 29 and used in similar studies.We will evaluate internal and external validity by assessing risk of biases, inconsistencies, conflicts of interests and author declarations.We will enter quality appraisal variables into a template for an overview.

| Synthesis of results
We will present the data extracted in a tabular format.The format will mirror the objective and research questions of the systematic review.
Furthermore, we will perform a meta-analysis of the included literature as per guidelines, if the included studies are sufficiently homogenous in design and comparators as per PEO criteria If applicable, we will measure treatment effect for dichotomous outcomes (event data) using risk ratio (RR) with 95% confidence interval (CI).We will evaluate between-study variability using I 2 .We will convert to consistent formats in time-to-event data analyses, if warranted.
Furthermore, a systematic narrative synthesis of the included literature will support the data, including text and tables to describe the characteristics and findings of the included literature.

| Meta-biases
To assess publication and dissemination bias, we will explore relevant databases for protocols of the included studies.Furthermore, we will  T A B L E 3 Quality appraisal instrument.

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E Y W O R D S dispatch, emergency medical services, outcome, response time 1 | INTRODUCTION 1.1 | Rationale al Paper 13 et al Paper 14 et al Paper 15 et al Paper 16 et al Paper 17 et al Paper 18 et al Paper 19 et al Paper 20 et al Paper 21 et al Paper 22 et al Paper 23 et al Paper 24 et a Paper 25 et al Paper 26 et al Paper 27 et al Paper 28 et al Paper 29 et al Paper 30 et al Paper 31 et al Paper 32 et al Abbreviations: EMS, emergency medical services; N, no; Y, yes; ?, unclear.
al Paper 10 et al Paper 11 et al Paper 12 et al Paper 13 et al Paper 14 et al Paper 15 et al Paper 16 et al Paper 17 et al Paper 18 et al Paper 19 et al Paper 20 et al Paper 21 et al Paper 22 et al Paper 23 et al Paper 24 et al Paper 25 et al Paper 26 et al Paper 27 et al Paper 28 et al Paper 29 et al Paper 30 et al Paper 31 et al Paper 32 et al Abbreviations: EMS, emergency medical service; N, no; Y, yes; ?, unclear/not applicable.
Note: This checklist has been adapted for use with protocol submissions to Systematic Reviews from Table3in Moher D et al: Preferred reporting items for systematic review and meta-analysis protocols (PRISMA-P) 2015 statement.Systematic Reviews 2015 4:1.
T A B L E 2 T A B L E 2 (Continued)