Estimating core temperature with external devices after exertional heat stress in thermal protective clothing

Background. Temperature measurement is important for emergency medical services (EMS) providers when identifying and treating heat illness or infection. Direct measures of body core temperature (T_c) are often expensive (ingestible capsules) or impractical (rectal probes) in the field. Multiple devices for estimating T_c have been adopted by EMS providers, with little understanding of the agreement between these devices and T_c. Objective. To examine the agreement between the results of five external thermometers and T_c after subjects experienced physical exertion while wearing protective clothing. Methods. Fifty firefighters completed treadmill walking in thermal protective clothing in a hot environment. Measurements of core, temporal, tympanic, forehead, and skin temperatures were obtained during a 20-minute recovery period simulating emergency incident rehabilitation. Results. The mean bias of external thermometers ranged from -1.31°C to -3.28°C when compared with T_c and exceeded the predetermined clinical cutoff of ±0.5°C from T_c. The 95% limits of agreement ranged from 2.75°C to 5.00°C. Conclusions. External measuring devices failed to accurately predict T_c in hyperthermic individuals following exertion. Confidence intervals around the bias were too large to allow for reasonable estimation of T_c. EMS providers should exercise caution when using any of these temperature estimation techniques.