HHS (Hyperosmolar Hyperglycaemic State) is the quiet counterpart to DKA. It develops slowly in older type 2 diabetics with residual insulin, leading to extreme hyperglycaemia and dehydration without ketosis. In this 2-hour deep dive, Jonathan explains why HHS kills through water loss and hyperviscosity rather than acid, and how to manage it safely.

Key Learning Points:

· Pathophysiology: Relative insulin deficiency → no ketones, but relentless osmotic diuresis → hyperosmolarity > 320 mOsm/kg.

· Recognition: Elderly, confused, profoundly dehydrated, glucose often > 30 mmol/L, Na⁺ high, pH > 7.3.

· Fluids first: Replace ~½ deficit in 12 h with 0.9 % saline; adjust for heart/kidney function.

· Insulin later: 0.05 u/kg/hr once osmolality is falling; aim glucose fall 3–6 mmol/L/hr.

· Add dextrose when glucose ≈ 14 mmol/L to avoid cerebral oedema.

· Potassium vigilance: Replace according to level; withhold insulin if

· Thromboprophylaxis essential.

· Monitoring: Hourly glucose & neuro obs, 2–4-hourly U&Es/osmolality, strict fluid balance.

· Complications: Cerebral oedema, VTE, renal injury, electrolyte shifts, rhabdomyolysis.

· Take-home: In HHS, correct the water slowly, the sugar gently, and never forget the brain.