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Accidental hypothermia

BMJ 2006; 332 doi: (Published 23 March 2006) Cite this as: BMJ 2006;332:706
  1. Elliot Epstein, consultant in general and geriatric medicine (,
  2. Kiran Anna, medical senior house officer1
  1. 1 Walsall Manor Hospital, Walsall, West Midlands WS2 9PS
  1. Correspondence to: E Epstein

    Hypothermia is a life threatening condition, and management can be challenging, with little robust evidence to support the various treatments. This article should help doctors to understand the condition better

    Hypothermia can be defined as an unintentional fall in core body temperature below 35°C.1 It can be classified as mild (core body temperature 32.2-35°C), moderate (< 32.2-28°C), or severe (< 28°C).

    Why is temperature homoeostasis important?

    Maintaining a normal body temperature is essential for our metabolism to function optimally. The human body has developed an elaborate system for balancing heat production and heat loss.

    How is heat generated?

    In simple terms, heat is generated by the metabolic processes that occur within the tissues of the body, such as fat and muscle.2 Metabolic rate refers to the rate of heat liberated during these chemical reactions.2 In a cold environment, involuntary contraction and expansion of muscle groups generates warmth. This process is known as shivering.

    How is heat lost from the body?

    Heat is lost by radiation, conduction, convection, and evaporation.2

    • Radiation—Loss of heat may occur to surrounding cooler objects in the form of infrared radiation

    • Conduction—Heat may be lost to objects close to the skin, such as a chair, a bed, or the floor. Heat may also be lost by conduction to the surrounding air

    • Convection—Removal of body heat by air currents

    • Evaporation—Heat may be lost by evaporation of water from the body.

    How is core body temperature regulated?

    Thermoreceptors are located centrally and peripherally.1 2

    Clinical tips

    As a general rule

    • Mild hypothermia should usually be treated with passive rewarming

    • Moderate and severe hypothermia should usually be treated with active rewarming

    Summary points

    Older adults and people with debilitating disease and malnutrition are at risk of hypothermia

    Hypothermia may be mild, moderate, or severe. If severe, patients are at risk of lethal arrhythmias and respiratory failure

    Rewarming methods include giving warm intravenous fluids, using forced air rewarming systems, and covering the …

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