Describe hypothermia and the local effects of cold.

Hypothermia

• Predisposing factors — alcohol, which causes peripheral vasodilatation, impairs shivering and abolishes judgement, and is present in a very large proportion of cases; the extremes of age, the elderly having reduced perception of cold and reduced heat generation, and neonates a large surface area; wet clothing and wind, which multiply heat loss; immersion in cold water, which cools the body 25 times faster than air; homelessness, poverty and malnutrition; hypothyroidism, hypoglycaemia and hypopituitarism; and sedative and antipsychotic drugs
• Autopsy findings — pink or bright red lividity, because oxyhaemoglobin does not dissociate at low temperature and the tissues do not take up oxygen — and this must not be mistaken for carbon monoxide; frostbite of the exposed parts; wischnewsky spots, small brown or black submucosal haemorrhagic erosions in the gastric mucosa, which are characteristic though not entirely specific; haemorrhagic pancreatitis; and a raised blood ketone level
• The diagnosis is largely circumstantial, resting on the temperature and the environment; the autopsy findings support it rather than establishing it

• "Nobody is dead until warm and dead.
• " Severe hypothermia mimics death exactly — fixed dilated pupils, no palpable pulse, no detectable respiration, rigidity — and yet the profound cooling protects the brain, and full neurological recovery has followed hours of apparent death, particularly in children after cold-water drowning.
• Resuscitation is continued while the patient is rewarmed, and death is not declared until the core temperature is normal.

Frostbite and Local Cold Injury

• Frostbite is the freezing of tissue, with ice crystal formation, cellular dehydration and vascular thrombosis. It affects the peripheries — fingers, toes, ears, nose and cheeks — and is graded like a burn: first degree with erythema and oedema, second with blisters, third with full-thickness skin loss, and fourth involving deep tissue and bone with eventual gangrene and auto-amputation
• Trench foot (immersion foot) — prolonged exposure to cold and wet without freezing; the tissue is macerated, painful and swollen, and may proceed to gangrene
• Chilblains (pernio) — itchy erythematous swellings on the extremities after repeated exposure to cold and damp above freezing
• Rewarming of frostbite is by rapid immersion in water at 40 to 42°C; it is intensely painful and requires analgesia. Rubbing or applying dry heat or snow is harmful, and rewarming should not be attempted if there is any risk of RE-freezing, since a freeze-thaw-freeze cycle is far more destructive than continued freezing

Medicolegal Aspects and Applied Aspects

• Manner — accidental in almost all cases, in the homeless, the intoxicated, the elderly living alone, mountaineers and those lost in cold regions; and in India, deaths in the north during winter cold waves among the homeless and the poorly housed are a recurrent public health problem. homicidal by exposure of an infant or a helpless person — which is a form of neglect; and rarely suicidal
• Do not misinterpret paradoxical undressing; a body found partly or wholly undressed in a cold environment, with the clothing scattered nearby, is a recognised feature of hypothermia and is regularly and wrongly reported as evidence of a sexual assault
• Do not mistake pink lividity for carbon monoxide; cold produces the same appearance, and the environment and carboxyhaemoglobin estimation settle it
• Rewarm slowly in moderate hypothermia and handle the patient gently; rough movement can precipitate ventricular fibrillation in a cold heart, and afterdrop — a further fall in core temperature as cold peripheral blood returns to the centre — may occur with rapid external rewarming
• Continue resuscitation until the core temperature is above 32 to 35°C before declaring death, and use active internal rewarming in severe cases; the standard signs of death are unreliable in a cold body
• Look for Wischnewsky spots at autopsy, and record the ambient conditions and the clothing; the diagnosis is circumstantial and the scene information cannot be recovered afterwards
• Consider neglect where an elderly, disabled or very young person dies of cold in a household where others were warm; the same reasoning applies as in starvation
• Alcohol is present in a large proportion of hypothermia deaths; it dilates the peripheries, abolishes shivering and destroys judgement, and creates a false sensation of warmth
• Cessation of shivering is an ominous sign, not an improvement; it marks the transition from mild to moderate hypothermia and the loss of the last compensatory mechanism
• Immersion cools 25 times faster than air, which is why cold-water immersion produces profound hypothermia within minutes and why it is also the setting of the most remarkable recoveries
• Do not rewarm frostbite if re-freezing is possible; a freeze-thaw-freeze cycle destroys more tissue than continuous freezing does