Diabetes: acute complications (DKA, HHS)
- Mechanism
Very high sugar can turn the blood acidic (ketoacidosis) or dangerously concentrated (hyperosmolar state). Too much treatment can make sugar fall too low.
What it is
Diabetic ketoacidosis occurs when insulin is absent or almost absent and counter-regulatory hormones are high, so fat breakdown floods the liver with fatty acids that become ketone bodies. The hyperosmolar hyperglycaemic state occurs when there is enough insulin to prevent ketosis but not hyperglycaemia, typically in older people with type 2 diabetes and poor fluid intake. Hypoglycaemia is the commonest acute complication of treatment.
Step by step
- Insulin deficiency removes the brake on hormone-sensitive lipase in fat.
- Free fatty acids flow to the liver, where high glucagon activates carnitine palmitoyltransferase and beta-oxidation.
- Acetyl-CoA is diverted to ketone bodies, overwhelming buffers: anion-gap acidosis.
- Unopposed gluconeogenesis and glycogenolysis plus lack of uptake raise glucose: osmotic diuresis and dehydration.
- Fluid and electrolyte losses, acidosis and shock can be fatal without insulin, fluids and potassium.
DKA and HHS compared
| Feature | Ketoacidosis | Hyperosmolar state |
|---|---|---|
| Typical patient | Type 1, young | Type 2, older |
| Insulin | Almost absent | Some present |
| Ketones and acidosis | Marked | Minimal |
| Glucose | High | Very high |
| Osmolality and dehydration | Raised | Very raised, profound dehydration |
| Onset | Hours to a day | Days |
| Mental status | Often clear or drowsy | Often confused or comatose |
Clinical notes
- Cerebral oedema is a feared complication of DKA treatment in children.
- Repeated hypoglycaemia blunts the warning symptoms (hypoglycaemia unawareness).
- SGLT2 inhibitors can cause euglycaemic ketoacidosis.
Test yourself
Think of the answer, then tap the question to see it.
Why is total body potassium low in DKA even when serum potassium is high?
Acidosis and lack of insulin shift potassium out of cells, and osmotic diuresis loses it in urine.
Why is ketosis minimal in the hyperosmolar hyperglycaemic state?
Enough insulin remains to suppress lipolysis and hepatic ketogenesis, though not enough to control glucose.
What causes Kussmaul breathing in DKA?
Respiratory compensation for metabolic acidosis: deep, rapid breaths to blow off carbon dioxide.
Elsewhere in DurgiPedia
- Physiology of diabetes and ketoacidosis
- Metabolic acidosis, the anion gap and compensation
- The physiological response to hypoglycemia
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Diabetic ketoacidosis: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2025); Diabetic hyperglycemic hyperosmolar syndrome: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2025); Hypoglycemia: MedlinePlus (MedlinePlus, US National Library of Medicine, 2025).
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Representative model, for educational purposes only.