Hyperosmolar, non-ketotic coma (HONK) - Complications of diabetes

Hyperosmolar, non-ketotic coma (HONK)

Definition

This occurs in people who have type 2 diabetes mellitus and is characterised by hyperglycaemia without severe hyperketonaemia or metabolic acidosis.

Age

More common in the elderly.

Sex

M = F

Aetiology

Precipitating factors include infection, myocardial infarction and stroke, or diabetogenic drugs such as glucocorticoids and thiazide diuretics.

Pathophysiology

The pathophysiology is essentially the same as for diabetic ketoacidosis (DKA), except that because the person has enough insulin to suppress lipolysis and ketogenesis, uncontrolled ketogenesis does not occur. There is insufficient insulin to prevent increased glucose production and reduced glucose uptake by cells and so hyperglycaemia occurs. The hyperglycaemia is often much more extreme than in DKA and causes severe hyperosmolarity with an osmotic diuresis which unless compensated for by water intake leads to progressive severe dehydration. This compounds the hyperos-molarity caused by the hyperglycaemia, which increases blood viscosity, predisposing to thromboembolic disorders. If untreated, it leads to confusion and eventually coma.

Clinical features

Often occurs in elderly undiagnosed patients, who present with polyuria, intense thirst, weight loss and blurred vision. The symptoms and signs of ketoacidosis are absent (hyperventilation, ketotic breath) but confusion, drowsiness and coma are more common.

Complications

Thromboembolic disease, such as stroke, mesenteric artery thrombosis, deep vein thrombosis and pulmonary embolism.

Investigations

·        Blood and urinary ketones are absent or only slightly raised.

·        Blood glucose is raised and can be as high as 100 mmol/L.

·        U&Es: Markedly raised sodium (often over 155 mmol /L) and urea due to dehydration.

·        Very high plasma osmolality (>350 mosmol/kg) but anion gap is normal, as is pH on arterial blood gas.

·        Full blood count, blood cultures, urine culture, CXR and ECG are checked to identify underlying causes and complications. Consider cardiac enzymes in older patients.

Management

Patients require emergency fluid resuscitation with normal saline and potassium replacement (as for diabetic ketoacidosis). Low-dose intravenous insulin is used to reduce the hyperglycaemia but patients are often very sensitive and rapid reductions in glucose should be avoided. Prophylactic low-dose heparin to prevent thromboembolic complications. Any underlying cause should be identified and treated.

Prognosis

Mortality is higher overall (∼30%) than DKA, because these patients are more elderly.