Synopsis
Recognise adult hyperosmolar hyperglycaemic state, restore volume gradually, track osmolality and introduce insulin only at the correct physiological stage.
- Typical HHS combines marked hypovolaemia with glucose at least 30 mmol/L, calculated osmolality at least 320 mOsm/kg, minimal ketonaemia and no substantial ketoacidosis, but the whole syndrome matters more than one threshold.
- Calculate osmolality using the JBDS expression 2 × sodium + glucose + urea, with all components in mmol/L, and plot it against glucose, sodium and fluid balance.
- Correct gradually: the usual osmolality target is a fall of 3–8 mOsm/kg/hour and glucose should not fall faster than 5 mmol/L/hour.
- Use 0.9% sodium chloride as the principal initial fluid, tailoring rate to haemodynamics, age, renal function and heart failure rather than copying a DKA timetable.
- Do not start insulin immediately in uncomplicated HHS; fluid alone lowers glucose and restores circulation, whereas premature insulin can shift water intracellularly and precipitate cardiovascular collapse.
- When glucose stops falling after adequate fluid, commence fixed-rate intravenous insulin at 0.05 units/kg/hour under the HHS protocol; earlier insulin is reserved for specified ketonaemic or mixed presentations.
- A rising measured sodium is expected as glucose falls and does not by itself justify hypotonic fluid if osmolality is declining at the safe target rate.
- Search actively for infection, infarction, stroke, medicines, dehydration, care dependency and new diabetes, then plan rehabilitation because recovery may take several days.
Key red flags
Several days of thirst, polyuria, weakness, weight loss and declining intake may progress to severe dehydration, tachycardia, hypotension and oliguria.
Confusion, drowsiness, visual change, focal signs, seizure or coma becomes more likely with severe or rapidly changing osmolality and requires parallel neurological assessment.
Classical HHS has blood ketones no higher than 3.0 mmol/L with pH at least 7.3 and bicarbonate at least 15 mmol/L despite profound hyperglycaemia.
Marked hyperosmolality can coexist with ketones above 3.0 mmol/L and acidosis; this overlap uses the DKA insulin rate with HHS-informed fluid caution and specialist oversight.
Fever, cough, dysuria, acute ischaemic symptoms, medication change, reduced care support or inability to reach water can reveal the driver and alter immediate management.
Unilateral swelling, hypoxia, chest pain, limb ischaemia or new focal neurology demands urgent investigation because severe dehydration and immobility create a prothrombotic state.
Investigation priorities
Confirm the hyperosmolar syndrome and quantify the hourly rate of physiological correction.
Management branches
An adult has extreme hyperglycaemia, dehydration, cognitive change or a prolonged osmotic prodrome.
- Perform ABCDE and obtain bedside glucose, blood ketones, venous gas, sodium, potassium, urea and creatinine, then calculate and record osmolality immediately.
- Assess volume, consciousness, oxygenation, urine output, comorbidity and thrombosis while searching for infection, vascular events and medicines that precipitated deterioration.
- Classify typical HHS, mild ketonaemia without acidosis or mixed DKA/HHS because insulin timing and dose differ, and involve senior diabetes and critical-care clinicians accordingly.