Heat and Emergency Department Operations: A Two-Decade Observational Study

Emergency department (ED) crowding remains one of the most pressing challenges facing the US healthcare system; environmental factors have received little attention as determinants of ED operational performance, patient behavior, or emergency service utilization. We examined the association between maximum daily heat index and ED throughput metrics, patient behavioral outcomes, and likelihood of EMS arrival. We retrospectively analyzed 485,403 warm-season ED visits from a 22-year period at a large urban academic medical center in New England. The exposure was daily maximum heat index (ERA5-Land) for Suffolk County, Massachusetts. Primary outcomes included four ED throughput time metrics: door-to-doctor time, doctor-to-decision time, boarding time, and total ED length of stay; secondary outcomes included the left without being seen rate, leaving against medical advice rate, and likelihood of EMS arrival. Each 1°F increase in heat index was associated with a 0.41% increase in door-to-doctor time (95% CI: 0.38% – 0.44%). Heat index was not significantly associated with the other three throughput metrics. At the 95°F heat index threshold, patients were 27% more likely to leave against medical advice than on days below the threshold (OR 1.27; 95% CI: 1.02 – 1.58), and had higher odds of arriving by EMS (OR 1.10; 95% CI: 1.06 – 1.15). Higher heat index was associated with longer door-to-doctor time, increased EMS arrival proportion, and higher odds of leaving against medical advice. Health systems and municipalities should characterize how hot weather affects operational performance and integrate this evidence into heat-readiness planning.