The Impact of Heat Waves on Transport Volumes in an Urban Emergency Medical Services System: A Retrospective Review

Abstract

Heat waves pose a serious public health risk to particular patient populations, especially in urban areas. Emergency Medical Services (EMS) in many urban areas constitute the first line of regional preparation and response to major heat wave events; however, little is known on heat wave operational impact to the EMS system, such as call volume or demand. To examine the effect of heat wave periods on overall urban EMS system call volume and transport volume as well as the nature of the call types. Retrospective review of all emergency medical calls to an urban, two-tiered EMS system performed over a 5-year period from 2006-2010. Heat wave days (HWD) defined as two or more consecutive days of hot weather >32.2°C (90°F) were compared with similar non-heat wave days (nHWD) of the previous year to also include two calendar days prior to and after the heat wave. National Weather Service (NWS) temperature data, daily EMS call volume data, and call type codes were collected and underwent descriptive analysis. Thirty-one HWD were identified and compared with 93 nHWD. The mean maximum temperature for HWD was 34°C (93.2°F) compared with 25.3°C (77.6°F) for nHWD (P < .001). Average daily medical emergency calls (318.4 vs 296.3, P < .001) and actual patients transported per day (247.5 vs 198.3, P < .001) were significantly higher during HWD. There was no difference in daily medical emergency call volume or EMS transports between weekdays or weekend days. No significant differences on various call types were observed between HWD and nHWD except for "heat" related calls (7.7 vs 0.5, P < .001). Emergency Medical Services call volumes were significantly increased during heat waves, however there was minimal change in the types of calls received.