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Relationship Between Emergency Ambulance Response Times, Patient Acuity and Demographics in Aotearoa New Zealand

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Thesis embargoed until 25th April 2026(1.74 MB)

Date

2024

Authors

Ohs, Daniel

Supervisor

Todd, Verity
Howie, Graham
Swain, Andy

Item type

Thesis

Degree name

Master of Philosophy

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Publisher

Auckland University of Technology

Abstract

The most basic function of ambulance Emergency Medical Services (EMS) is to respond to urgent, unplanned health needs in the community in an appropriate and timely manner. To enable this, ambulance services have developed sophisticated systems to triage calls for help. Callers are asked questions from a scripted call-handling algorithm that prioritises their call based on the potential threat to life. Each call is allocated a dispatch triage priority, and each dispatch triage priority is associated with a response time target (the time it should take for an ambulance to locate the scene). Whilst this is common practice, there is little empirical evidence surrounding the benefit and efficacy of these systems. This thesis aims to better describe the relationship between ambulance response times and patient acuity. It also aims to understand if receiving a timely ambulance response is associated with specific patient demographics (age, sex, ethnicity, social deprivation, and rurality) or with clinical characteristics (dispatch triage priority, patient status, and clinical impression). Firstly, a scoping literature review was completed to understand what contemporary international research evidence is already available. Thirteen articles met the inclusion criteria; these were further categorised into two areas. Nine articles reviewed aspects of the Medical Priority Dispatch System (MPDS) and its overall efficacy in generating determinants that drive ambulance dispatch priority. These studies found that MPDS has a high sensitivity but low specificity in identifying time-critical patients. The other four articles studied aspects of ambulance response times and their link with patient outcomes. These studies found that, while there is a widely accepted view that fast response times equate to better outcomes, this was not evident from the reviewed literature (outside of time-critical emergencies such as major trauma). Secondly, a quantitative retrospective observational study was conducted, examining data related to Emergency Medical Service (EMS) response times over one month. The primary outcome was the timeliness of ambulance response relative to response time targets (RTT). There were 32,812 ambulance attendances included in the study, with 15,229 (46.4%) of patients receiving an ambulance response within the respective target. Our study demonstrated that calls that received a life-threatening dispatch triage priority (PURPLE, RED1 and RED2) had significantly lower odds of receiving an ambulance within the RTT (p < 0.001; aOR 0.52, 95% CI: 0.42-0.66, aOR 0.64, 95% CI: 0.60-0.69, and aOR 0.66, 95% CI: 0.61-0.71, respectively). However, patients assessed by ambulance personnel at the scene as having a life-threatening problem (Status One or Status Two), had significantly higher odds of receiving an ambulance within the RTT (p < 0.001; aOR 1.50, 95% CI: 1.17-1.93 and aOR 1.26, 95% CI: 1.11-1.44, respectively). When examining patient demographics, patients of Asian or Pacific descent had significantly lower odds of receiving an ambulance within the RTT (p < 0.001; aOR 0.83, 95% CI: 0.74-0.93 and aOR 0.64, 95% CI: 0.57-0.71, respectively). Conversely, those needing an ambulance in the most deprived (Quintile 5) areas, and those living rurally had significantly higher odds of receiving an ambulance within the RTT (p < 0.001; aOR 1.44, 95% CI: 1.28-1.63 and aOR 1.44, 95% CI: 1.37-1.52, respectively), as did patients suffering from collapse, metabolic problems, and trauma (p < 0.001; aOR 1.34, 95% CI: 1.18-1.53 and aOR 1.25, 95% CI: 1.09-1.43 and aOR 1.14, 95% CI: 1.04-1.26, respectively). We did not observe a significant difference in the odds of receiving an ambulance attendance within the RTT in Māori patients (p < 0.001; aOR 0.98, 95% CI: 0.91-1.05). The findings demonstrate a disconnect between patient acuity, equity, and ambulance response times in some instances. They call into question the use of RTTs, which are likely to be more a measure of service efficiency and patient experience rather than an enabler of enhanced clinical outcomes.

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http://hdl.handle.net/10292/18189

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