Heat-related illness in the African wilderness

Abstract

A fit-looking 23-year-old male participant in a summer mountain trail run collapses 3 km from the end of the 25 km race. Despite the altitude, ambient temperatures are warm, and the participants have been exposed to the full sun for several hours. On your first assessment, he is very confused, with a weak, rapid pulse (160 beats per minute). His skin is wet and cool. A passing member of the same running club alleges that he is not known to have any medical conditions. You notice that his water bottles are both empty. As fellow runners help you carry him to the nearby medical-aid station, a rapidly expanding differential diagnosis fills your thoughts. BackgroundWilderness heat-related illnesses span a continuum of medical problems caused by the generation of, and/or exposure to, excessive heat in the wilderness environment. They can range from minor annoyances to life-threatening conditions. Endogenous heat production is directly dependent on the sum of that from inescapable sources, such as basal cellular metabolism and cardiorespiratory work, and heat generated by physical exertion. All heat exchange (gain or loss) occurs through four mechanisms: conduction, convection, radiation and evaporation. Conduction refers to the direct transfer of heat from one object to another through contact. Convection is heat gain or loss due to movement of a fluid (such as air); a convection oven or wind chill from an Antarctic breeze are similar examples. Radiation describes transfer of heat through electromagnetic waves, epitomised by the heat of the sun on skin. Evaporation is the loss of heat induced by the phase change from liquid to gas, which is dramatically affected by ambient vapour pressure or relative humidity.Many animals have developed ingenious strategies to adapt their physiology to control heat gain or loss. Indeed, it is hypothesised that particular human traits -our upright stance, complex bony structure of the foot, nuchal ligament, relatively hairless skin and copious capacity for perspiration -evolved to give us an advantage in chasing down prey in the prehistorical African heat.[1] Today, however, humans are unique in their ability to adapt the environment to control their physiology through behaviour and material means: use of clothing, shelter, and devices such as heaters and air conditioners. Despite this, we cannot alter the laws of thermodynamics, and people in the wilderness are subject to the same exposure and thermal exchange mechanisms as our primitive ancestors. Fortunately, the development of modern science, clothing technology, and an understanding of physiology allow us to function successfully in environments of extreme heat under many adverse circumstances (Fig. 1).Risk factors traditionally considered to increase our susceptibility to the deleterious effects of heat stress include obesity, lack of acclimatisation to hot environments, poor physical fitness, extremes of age, underlying illness (e.g. cardiac conditions, hyperthyroidism), dehydration, certain medications (e.g. beta blockers, anti...

Growing wilderness and expedition medicine education in southern Africa

“…Finally, heat-exposure injury is discussed in the African context. [23][24][25] While far from a comprehensive review of wilderness and expedition medicine, it is the fervent hope of the authors that these topics provide a catalyst for awareness and a kernel for further discussion, interaction and development of the field in SA, and an emergence of the specialty on our continent.…”