Background
To reduce morbidity and mortality from cold exposure it is vital to develop simple prehospital methods that can be improvised and used immediately by first responders and casualties to maintain body temperature and prevent hypothermia. Building membrane and hot water bottles can be improvised in low-resource environments, for example, salvaged from destroyed buildings after natural disasters. Wrapping casualties in vapour-proof barriers, such as foil blankets or polythene survival bags, is a common pre-hospital method, although over time casualties become damp which exacerbates body cooling. Hot water bottles reduce body cooling in animals receiving anaesthesia; however, their effectiveness in reducing cold stress in humans remains to be established. Therefore, this study determined the effectiveness of barrier wraps constructed from vapour-proof foil blanket and vapour-permeable building membrane, with and without three improvised 1-litre hot water bottles, to reduce cold stress of no protection in a cold environment.
Methods
The study received a favourable ethics opinion from the School of Psychology and Sport Science Academic Research Ethics Committee and written informed consent from all participants. Fourteen young healthy participants (10 men, 4 women) completed six conditions: 1. No protective barrier wrap in 26°C, 2. No protective barrier wrap in 10°C, 3. Vapour-permeable building membrane barrier wrap in 10°C, 4. Building membrane barrier wrap plus three 1-litre 73°C hot water bottles in 10°C, 5. Vapour-proof foil blanket wrap in 10°C, 6. Foil blanket wrap plus three hot water bottles in 10°C. All conditions were 20 min and completed in an environmental chamber, whilst participants lay supine, dressed in shorts, t-shirts, socks, and trainers. Cold stress was quantified by thermometry (core (Tc) and mean skin temperature (₸sk)), indirect calorimetry (metabolic heat production (H)), and subjective thermal judgement scales. The data were analysed by ANOVA and Tukey’s tests. Post hoc Tukey’s tests are presented in the text as mean differences [95% confidence interval].
Results
No differences were detected in physiological and perceptual responses between the building membrane and foil blanket barrier wraps (Interactions: Tc P = 0.74, ₸sk P = 0.19, H P = 0.87, thermal sensation P = 0.36, thermal comfort P = 0.29, thermal tolerance P = 0.09). Compared with no protection, participants wrapped in barriers had 5% higher ₸sk (1.2°C [1.0, 1.5]), 18% lower H (-12 W·m−2 [-15, -8]), 46% higher thermal sensation (1.3 [0.7, 1.9]), 42% higher thermal comfort (-0.8 [-1.2, -0.5]), and 54% higher thermal tolerance (-0.9 [-1.2, -0.6]). There were no detectable differences in ₸sk (-0.1°C [-0.2, 0.1] and H (1 W·m−2 [-1, 3]) between barriers alone and barriers with hot water bottles. However, participants wrapped in barriers with hot water bottles felt warmer (67% higher thermal sensation; 1.0 [0.5, 1.5]), more comfortable (45% higher thermal comfort; -0.4 [-0.7, -0.2]), and better able to tolerate the cold environment (50% higher thermal tolerance; -0.9 [-1.6, -0.3]) than when wrapped in barriers alone.
Conclusion
Barrier wraps constructed from building membrane were as effective as foil blankets in reducing physiological and perceived cold stress, and adding hot water bottles further reduced perceived but not physiological cold stress.