Caldwell Aaron R, Saillant Michelle M, Pitsas Dina, Johnson Audrey, Bradbury Karleigh E, Charkoudian Nisha
Thermal and Mountain Medicine Division, United States Army Research Institute of Environmental Medicine, Natick, MA 01760, USA.
Oak Ridge Institute of Science and Education, Belcamp, MD 21017, USA.
Mil Med. 2022 Aug 25;187(9-10):e1017-e1023. doi: 10.1093/milmed/usac047.
Exertional heat illnesses remain a major threat to military service members in the United States and around the world. Exertional heat stroke (EHS) is the most severe heat illness, characterized by core hyperthermia and central nervous system dysfunction. Per current Army regulations, iced-sheet cooling (ISC) is the recommended immediate treatment for heat casualties in the field, but concerns have been raised regarding the efficacy of this approach. Thus, the purpose of this study was to quantify the cooling rate of ISC following exertional hyperthermia.
We utilized a randomized crossover design with 2 experimental trials. In both trials, exertional hyperthermia was induced by walking (3.5 mph at 5% grade) on a treadmill in an environmental chamber (40 °C, 30% RH) for up to 3 hours or until core body temperature reached 39.2 °C. After the walking portion, individuals either received ISC (experimental trial) or cooling and rested supine in the same environmental conditions for 30 minutes with no ISC (control trial). For ISC, bed sheets soaked in ice water were applied (per Army guidance) at the neck, chest, and groin with another sheet covering the body. Sheets were rotated and resoaked every 3 minutes until core temperature decreased to <38.0 °C.
By design, participants finished exercise with increased core temperature (38.8 ± 0.39 °C vs. 38.90 ± 0.34 °C, ISC and control trials, P = 1.00). The ISC trial provided significantly (P = .023) greater cooling rates, 0.068 °C/min 95% confidence interval [CI; 0.053, 0.086], compared to the control trial, 0.047 °C/min 95% CI [0.038, 0.056]. Additionally, the time to decrease to less than 38.0 °C was significantly (P = .018) faster in the ISC trial (median = 9.3 minutes) compared to the control trial (median = 26.6 minutes).
ISC increases the cooling rate of those recovering from exertional hyperthermia. With the observed cooling rate, we can extrapolate that ISC would reduce core temperature by ∼2 °C within 30 minutes during a case of EHS. We conclude that ISC provides a safe and effective alternative for the field where cold water immersion resources may not be readily available.
运动性热疾病仍然是美国及全球军事人员面临的主要威胁。运动性热射病（EHS）是最严重的热疾病，其特征为核心体温过高和中枢神经系统功能障碍。根据美国陆军现行规定，冰床单降温（ISC）是野外热伤亡人员推荐的即时治疗方法，但有人对这种方法的疗效提出了担忧。因此，本研究的目的是量化运动性体温过高后ISC的降温速率。
我们采用了随机交叉设计，包含2个实验性试验。在两个试验中，通过在环境舱（40°C，30%相对湿度）的跑步机上行走（3.5英里/小时，坡度5%）长达3小时或直到核心体温达到39.2°C来诱发运动性体温过高。在行走部分结束后，个体要么接受ISC（实验性试验），要么在相同环境条件下仰卧休息30分钟且不进行ISC（对照试验）。对于ISC，按照陆军指南，将浸泡在冰水中的床单敷于颈部、胸部和腹股沟，并用另一床单覆盖身体。每隔3分钟更换并重新浸泡床单，直到核心体温降至<38.0°C。
按照设计，参与者完成运动时核心体温升高（ISC试验为38.8±0.39°C，对照试验为38.90±0.34°C，P = 1.00）。与对照试验（0.047°C/分钟，95%置信区间[CI；0.038，0.056]）相比，ISC试验的降温速率显著更高（P = 0.023），为0.068°C/分钟，95% CI [0.053，0.086]。此外，与对照试验（中位数 = 26.6分钟）相比，ISC试验中降至低于38.0°C的时间显著更快（P = 0.018）（中位数 = 9.3分钟）。
ISC提高了运动性体温过高恢复者的降温速率。根据观察到的降温速率，我们可以推断，在EHS病例中，ISC可在30分钟内使核心体温降低约2°C。我们得出结论，在可能无法随时获得冷水浸泡资源的野外，ISC提供了一种安全有效的替代方法。
