An unintentional reduction of core body temperature below the normal physiological limits.

• Mild hypothermia: 32-35°C
• Moderate or severe hypothermia: 28-32
• Severe hypothermia: <28

Epidemiology:

• The incidence of hypothermia varies globally. In the UK, the estimated annual number of hypothermia-related deaths is 300/year, whereas in Canada, it is 8000/year.
• Hypothermia is most common during the winter, and the elderly are particularly susceptible. Many cases of hypothermia also occur indoors, due to poor heating facilities.

Pathophysiology:

In initial stages, thermoreceptors in the skin and subcutaneous tissues sense the low temperature and cause a regional vasoconstriction. This causes the hypothalamus to stimulate the release of TSH and ACTH. It also stimulates heat production by promoting shivering.

Causes:

• Exposure to cold in the environment is the major cause
• Inadequate insulation in the operating room
• Cardiopulmonary bypass
• Newborn babies.

Risk factors:

• General anaesthesia