Hyperosmolar Hyperglycaemic State
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Direct answer
Hyperosmolar hyperglycaemic state is a severe hyperglycaemic emergency defined by very high glucose, usually above 600 mg/dL, with serum osmolality above about 320 mOsm/kg and little or no ketosis. It differs from diabetic ketoacidosis because enough insulin is present to block lipolysis, but dehydration is far more profound and the patient is usually older with type 2 diabetes. Management begins with cautious intravenous fluids, with insulin and potassium added once the circulation and potassium allow.
What you must remember
- Diagnostic thresholds: glucose usually above 600 mg/dL, osmolality above about 320 mOsm/kg, pH above 7.30 and minimal ketones.
- Effective osmolality: 2 times sodium plus glucose in mg/dL divided by 18, with sodium in mmol/L.
- Pathophysiology: enough insulin to block lipolysis, but not enough to control hepatic glucose output, so ketosis is limited.
- Who gets it: older adults with type 2 diabetes, infection or stroke, reduced thirst or limited access to water, and drugs such as diuretics and steroids.
- Fluids first: isotonic saline initially; insulin and potassium are added once volume and potassium allow.
- Sodium correction: add about 1.6 mmol/L to sodium for each 100 mg/dL of glucose above 100.
- Thrombosis risk: raised, so prophylactic anticoagulation is commonly given.
A nursing home patient with confusion
A 74-year-old woman from a nursing home is confused and has had poor oral intake for several days. Her glucose is 900 mg/dL, sodium 136 mmol/L, and urea is raised.
- Calculate osmolality: Her effective osmolality is about 322 mOsm/kg, above the diagnostic threshold.
- Read the acid-base status: Her pH is 7.35 with a bicarbonate of 22 mmol/L and trace ketones.
- Correct the sodium: Corrected sodium is about 149 mmol/L, which means the measured sodium of 136 mmol/L hides true hypernatraemia.
- Seek the trigger: Infection is sought, usually urinary or chest.
- Replace fluid first: Initial management is isotonic saline, with the rate guided by haemodynamics and urine output. Dehydration is severe, so volume replacement is the first and most important step.
- Add insulin and potassium: Once fluid status improves and potassium is above the safe threshold, a low-dose insulin infusion is started and potassium is replaced.
- Correct sodium gradually: Sodium is corrected slowly, because a rapid fall in osmolality can cause neurological complications. Hourly glucose and neurological observations guide the insulin rate, and the team watches for cerebral oedema if osmolality falls too quickly.
Where the exam tries to catch you
The classic question is why insulin is not started first, and several traps cluster around that point.
- Trap: Starting insulin before fluids. Correct: Fluid restoration improves perfusion and lowers glucose by dilution, whereas insulin given into a collapsed circulation can cause hypotension and rapid potassium shifts.
- Trap: Excluding the diagnosis because ketones are negative. Correct: A negative or minimal ketone test does not exclude hyperglycaemic crisis when glucose is very high, so the diagnosis rests on osmolality and glucose.
- Trap: Reading the measured sodium as the true value. Correct: Sodium may look low or normal yet be truly high once corrected for glucose, so examiners expect the corrected value to be calculated.
- Trap: Ignoring potassium during insulin therapy. Correct: Insulin drives potassium into cells, so a potassium-depleted patient may develop dangerous hypokalaemia during treatment.
Frequently asked questions
What are the diagnostic thresholds for hyperosmolar hyperglycaemic state?
Hyperosmolar hyperglycaemic state is usually diagnosed when glucose exceeds 600 mg/dL, serum osmolality exceeds about 320 mOsm/kg, pH is above 7.30 and ketones are minimal. These thresholds distinguish it from diabetic ketoacidosis. Clinical signs of dehydration and altered consciousness support the diagnosis.
How is effective serum osmolality calculated in hyperosmolar hyperglycaemic state?
Effective serum osmolality is calculated as 2 times sodium in mmol/L plus glucose in mg/dL divided by 18. Urea is excluded because it does not drive water shift. A value above about 320 mOsm/kg in this setting supports hyperosmolar hyperglycaemic state.
Why is insulin not started first in hyperosmolar hyperglycaemic state?
Insulin is not started first because the circulation is usually severely dehydrated, and restoring volume with saline improves perfusion and lowers glucose. Insulin given into an underfilled circulation can cause hypotension and abrupt potassium shifts. Insulin is added once fluid status and potassium allow.
How does hyperosmolar hyperglycaemic state differ from diabetic ketoacidosis?
Hyperosmolar hyperglycaemic state has very high glucose, marked dehydration and minimal ketosis, whereas diabetic ketoacidosis has metabolic acidosis with significant ketones. Hyperosmolar hyperglycaemic state typically affects older adults with type 2 diabetes. Enough insulin is present in hyperosmolar hyperglycaemic state to block lipolysis.
How is hypernatraemia assessed in hyperosmolar hyperglycaemic state?
Hypernatraemia is assessed using corrected sodium, which adds about 1.6 mmol/L for each 100 mg/dL of glucose above 100. The measured sodium can look normal while the corrected value is truly high. Sodium is then lowered gradually to avoid neurological complications.