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Authors: Claire Jordan Wiggins, Riyad N.H. Seervai, Medical Students, Baylor College of Medicine, Houston, Texas, USA. DermNet NZ Editor in Chief: Adjunct A/Prof Amanda Oakley, Dermatologist, Hamilton, New Zealand. Copy edited by Gus Mitchell. June 2020.
Coma is a state of prolonged unconsciousness when the patient does not move or respond to a painful stimulus, light, or sound. Causes of coma include head injury, stroke, brain tumour, drugs, alcohol, diabetes mellitus, and infection.
Examination of the skin of a comatose patient may provide information about the cause of coma, and the effects of the coma on the body. Skin examination may provide clues to a pre-existing systemic medical condition that could predispose to coma, such as the skin changes that can occur with longstanding diabetes mellitus, or drug abuse.
Colour changes in the skin may reveal a potential cause of the coma.
Colourful skin changes and associated swelling provide important clues for cellulitis, venous stasis, or deep vein thrombosis, for example. The rash of meningococcaemia is characteristic.
Fluctuations in skin temperature may reflect the depth of a coma.
Traditionally associated with barbiturate overdose, coma blisters can develop in association with coma due to other causes such as in a diabetic coma. They are thought to be caused by hypotension-associated necrosis and pressure. Coma blisters appear within 48–72 hours of the onset of coma as multiple, tense, blood-filled blisters at pressure sites. They typically self-resolve after several weeks. Skin biopsy shows a subepidermal blister and sweat gland and sweat duct necrosis. Thrombi in dermal vessels is often a clue the coma is not drug-induced.
Immobile hospitalised patients are at risk for pressure ulcers, including comatose patients who cannot communicate their ischaemic pain. Prevention of pressure ulcer includes limiting pressure, friction, and shear, while managing comorbid conditions that may interfere with wound healing, such as diabetes.
Subungual haemorrhages in fingernails may be noted several weeks after hospital admission for coma. Firm pressure on the nailbed may be used repeatedly during a hospital admission to determine response to pain in comatose patients.
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