An easy-to-use prehospital indicator for recognition of severity in heat-related illness: An observational study in the Tokyo metropolitan area

Abstract Background: Quick transportation to the hospital is necessary to decrease mortality risk in patients with heat-related illnesses. This study aimed to establish a rapid, effective, easy-to-use indicator for healthcare providers and laypersons to identify the life-threatening severity of heat-related illness and facilitate quick transport of identified patients in a community setting. Methods: This observational study was conducted using a database from 2016. Information concerning the clinical severity of heat-related illness in patients (n=2528) upon arrival at the hospital was extracted from prehospital transportation records. Results: Patient-related risk factors included age, vital signs, location of the patient, and the severity of the illness. Respiratory rate (adjusted odds ratio [aOR], 3.34; 95% confidence interval [CI], 1.80–6.22), heart rate (aOR, 2.88, 95% CI, 1.57–5.29), axillary body temperature (aOR, 7.79, 95% CI, 4.02–15.1), and consciousness level (aOR, 38.3, 95% CI, 5.22–281.1) were independent factors associated with the severity of heat-related illness. Blood pressure was measured at the scene but was not found to be an independent factor relating to the severity of the patient's condition. A heart rate, respiratory rate, and body temperature of more than 120 beats/min, 24 breaths/min, and 38.6°C, respectively (highest areas under the ROC curves: 0.80, 95% CI 0.75–0.87; 0.73, 95% CI 0.67–0.81; and 0.83, 95% CI 0.77–0.91; respectively) were predictive of life-threatening conditions in patients with heat-related illnesses. Conclusions: Attention should be paid to changes in the vital signs of patients with heat-related illness. Tachycardia and tachypnea are particularly sensitive and easy-to use indicators for laypersons to facilitate quick identification and transport of patients before they decline to a life-threatening situation.