Thermoregulation in Cold Environments

Hypothermia is defined as a core temperature below 35°C (95°F). It can be considered mild (32°C to 35°C) (89.6°F to 95°F), moderate (28°C to 32°C) (82°F to 89.6°F), or severe (below 28°C)(82°F). When body tissue is exposed to cold, the cell membranes no longer function properly, fluid leaves the cell, cellular processes stop, and an electrolyte imbalance occurs. Cell death occurs as the water in and around the cells crystallizes. In response to cold, the brain attempts to stimulate heat production by the mechanisms of shivering, increased metabolism, and the reduction of blood flow to peripheral tissue to minimize heat loss (27).

In many ways, issues of cold exposure parallel those of heat exposure. Local and generalized injuries can occur. It is also critical to remember that cold-related problems can occur even with mild outdoor temperatures. For example, amenorrhea has been reported in female workers in poultry slaughterhouses who work in the cold. Death of a farm worker due to hypothermia has been reported from immersion in cold water, even in warm weather (28,29).

Wind can multiply the effect of cold. What may be a perfectly safe situation in calm air can result in significant cold-related injury in windy conditions. To assist in evaluating the effect of wind, the National Weather Service publishes a wind chill index (Figure 33.2) (30,31,32).

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