Hyperosmolar hyperglycaemic state (HHS)

Overview

•Blood glucose >30 mmol/L

•Serum osmolality >320 mOsm/kg - formula: 2(Na + K) + glucose + urea

•Serum bicarbonate >15 mmol/L and/or pH >7.3 (no significant acidosis)

•Ketones absent or minimal (<3 mmol/L; urine ketones ≤2+)

•Typically type 2 diabetes; may be first presentation in up to 25% of cases

Presentation

•Insidious onset over days to weeks - distinguishes from DKA

•Altered consciousness/confusion - severity correlates with degree of hyperosmolality

•Profound dehydration - dry mucous membranes, reduced skin turgor, tachycardia, hypotension

•Polyuria and polydipsia - early osmotic symptoms

•Focal neurological signs (seizures, hemiplegia) - cerebral dehydration; can mimic stroke

•No significant abdominal pain - useful differentiator from DKA

Investigations

•Capillary glucose - rapid bedside; >30 mmol/L raises strong suspicion

•Serum osmolality - calculated 2(Na+K) + glucose + urea; >320 mOsm/kg diagnostic

•Venous blood gas - pH and bicarbonate to exclude significant acidosis/distinguish from DKA

•Blood ketones - absent or <3 mmol/L in HHS; >3 mmol/L suggests mixed picture or DKA

•U&Es - note sodium may be falsely low due to hyperglycaemia; correct by adding 1 mmol/L Na per 3 mmol/L glucose above 5.5

•Cultures, CXR, ECG - identify precipitating cause (infection, MI)

Differential diagnosis

HHS vs DKA
FeatureHHSDKA
Diabetes typeType 2Type 1 (or 2)
OnsetDays to weeksHours to days
Blood glucose>30 mmol/L>11 mmol/L (often lower)
Osmolality>320 mOsm/kgMildly elevated
KetonesAbsent or minimal>3 mmol/L
pH>7.3<7.3
Bicarbonate>15 mmol/L<15 mmol/L
ConsciousnessOften impairedUsually preserved

Feature	HHS	DKA
Diabetes type	Type 2	Type 1 (or 2)
Onset	Days to weeks	Hours to days
Blood glucose	>30 mmol/L	>11 mmol/L (often lower)
Osmolality	>320 mOsm/kg	Mildly elevated
Ketones	Absent or minimal	>3 mmol/L
pH	>7.3	<7.3
Bicarbonate	>15 mmol/L	<15 mmol/L
Consciousness	Often impaired	Usually preserved

Management

🚨
Never give insulin as the first intervention in HHS. Without adequate fluid replacement first, insulin drives glucose intracellularly causing sudden intravascular volume depletion and cardiovascular collapse. Always establish IV fluids before insulin.

Step 1 · IV fluid resuscitation
10.9% NaCl - restore circulating volume first
2Target osmolality reduction no faster than 3-8 mOsm/kg/hr to avoid cerebral oedema
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Step 2 · Electrolyte correction
1Potassium replacement guided by U&Es - total body K depleted despite potentially normal/high serum K on admission; can fall sharply once fluids and insulin given
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Step 3 · Insulin
1Withhold insulin until glucose stops falling with fluids alone
2Only add insulin if ketones present or glucose not falling adequately with fluids
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Step 4 · Treat precipitant and prevent complications
1Antibiotics if infection identified
2LMWH - VTE prophylaxis (high thrombotic risk in HHS)

Prognosis

•Mortality ~15-20% - significantly higher than DKA; older patients, delayed presentation, serious precipitants