This study explores the impact of heatwaves on emergency calls for assistance resulting in service attendance in the Australian state of Queensland for the period from January 1, 2010 through December 31, 2019. The study uses data from the Queensland Ambulance Service (QAS), a state-wide prehospital health system for emergency health care.

A retrospective case series using de-identified data from QAS explored spatial and demographic characteristics of patients attended by ambulance and the reason for attendance. All individuals for which there was an emergency call to “000” that resulted in ambulance attendance in Queensland across the ten years were captured. Demand for ambulance services during heatwave and non-heatwave periods were compared. Incidence rate ratio (IRR) and 95% confidence intervals (CI) were constructed exploring ambulance usage patterns during heatwaves and by rurality, climate zone, age groups, sex, and reasons for attendance.

Compared with non-heatwave days, ambulance attendance across Queensland increased by 9.3% during heatwave days. The impact of heatwaves on ambulance demand differed by climate zone (high humidity summer with warm winter; hot dry summer with warm winter; warm humid summer with mild winter). Attendances related to heat exposure, dehydration, alcohol/drug use, and sepsis increased substantially during heatwaves.

Heatwaves are a driver of increased ambulance demand in Queensland. The data raise questions about climatic conditions and heat tolerance, and how future cascading and compounding heat disasters may influence work practices and demands on the ambulance service. Understanding the implications of heatwaves in the prehospital setting is important to inform community, service, and system preparedness.

During mass-casualty incidents (MCIs), prehospital triage is performed to identify which patients most urgently need medical care. Formal MCI triage tools exist, but their performance is variable. The Shock Index (SI; heart rate [HR] divided by systolic blood pressure [SBP]) has previously been shown to be an efficient screening tool for identifying critically ill patients in a variety of in-hospital contexts. The primary objective of this study was to assess the ability of the SI to identify trauma patients requiring urgent life-saving interventions in the prehospital setting.

Clinical data captured in the Alberta Trauma Registry (ATR) were used to determine the SI and the “true” triage category of each patient using previously published reference standard definitions. The ATR is a provincial trauma registry that captures clinical records of eligible patients in Alberta, Canada. The primary outcome was the sensitivity of SI to identify patients classified as “Priority 1 (Immediate),” meaning they received urgent life-saving interventions as defined by published consensus-based criteria. Specificity, positive predictive value (PPV) and negative predictive value (NPV) were calculated as secondary outcomes. These outcomes were compared to the performance of existing formal MCI triage tools referencing performance characteristics reported in a previously published study.

Of the 9,448 records that were extracted from the ATR, a total of 8,650 were included in the analysis. The SI threshold maximizing Youden’s index was 0.72. At this threshold, SI had a sensitivity of 0.53 for identifying “Priority 1” patients. At a threshold of 1.00, SI had a sensitivity of 0.19.

The SI has a relatively low sensitivity and did not out-perform existing MCI triage tools at identifying trauma patients who met the definition of “Priority 1” patients.