Diabetic coma pathophysiology
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Pathophysiology
Severe Hypoglycemia
People with type 1 diabetes mellitus who must take insulin in full replacement doses are most vulnerable to episodes of hypoglycemia. It is usually mild enough to reverse by eating or drinking carbohydrates, but blood glucose occasionally can fall fast enough and low enough to produce unconsciousness before hypoglycemia can be recognized and reversed. Hypoglycemia can be severe enough to cause unconsciousness during sleep. Predisposing factors can include eating less than usual, prolonged exercise earlier in the day, and heavy drinking. Some people with diabetes can lose their ability to recognize the symptoms of early hypoglycemia.
Unconsciousness due to hypoglycemia can occur within 20 minutes to an hour after early symptoms and is not usually preceded by other illness or symptoms. Twitching or convulsions may occur. A person unconscious from hypoglycemia is usually pale, has a rapid heart beat, and is soaked in sweat: all signs of the adrenaline response to hypoglycemia. The individual is not usually dehydrated and breathing is normal or shallow. A meter or laboratory glucose at the time of discovery is usually low, but not always severely, and in some cases may have already risen from the nadir that triggered the unconsciousness. Unconsciousness due to hypoglycemia is treated by raising the blood glucose with intravenous glucose or injected glucagon.
Advanced Diabetic Ketoacidosis
Diabetic ketoacidosis (DKA), if it progresses and worsens without treatment, can eventually cause unconsciousness, from a combination of severe hyperglycemia, dehydration and shock, and exhaustion. Coma only occurs at an advanced stage, usually after 36 hours or more of worsening vomiting and hyperventilation.
In the early to middle stages of ketoacidosis, patients are typically flushed and breathing rapidly and deeply, but visible dehydration, pallor from diminished perfusion, shallower breathing, and rapid heart rate are often present when coma is reached. However these features are variable and not always as described.
If the patient is known to have diabetes, the diagnosis of DKA is usually suspected from the appearance and a history of 1-2 days of vomiting. The diagnosis is confirmed when the usual blood chemistries in the emergency department reveal hyperglycemia and severe metabolic acidosis.
Nonketotic hyperosmolar coma
Nonketotic hyperosmolar coma usually develops more insidiously than DKA because the principal symptom is lethargy progressing to obtundation, rather than vomiting and an obvious illness. Extreme hyperglycemia is accompanied by dehydration due to inadequate fluid intake. Coma from NKHC occurs most often in patients who develop type 2 or steroid diabetes and have an impaired ability to recognize thirst and drink. It is classically a nursing home condition but can occur in all ages.