SIADHEmergency

68-year-old on sertraline with pneumonia; confusion, vomiting, one seizure; Na⁺ 116, serum osmolality 245, urine osmolality 480, urine Na 55; clinically euvolaemic

• Seizure or coma
• Vomiting with confusion
• Na⁺ <115
• High-risk features for osmotic demyelination

• Hypovolaemia (diarrhoea, diuretics)
• Heart failure, cirrhosis, nephrotic
• Hypothyroidism, adrenal insufficiency
• Cerebral salt wasting
• Primary polydipsia, beer potomania

• Admit: Symptomatic hyponatraemia or Na⁺ <125
• ICU: Seizures, coma, need for repeated 3% saline

• Symptoms, not the number, decide hypertonic saline.
• Exclude pseudohyponatraemia (lipids, protein) and hyperglycaemia (corrected Na⁺) first.
• Chronic hyponatraemia (>48 h) is the rule in hospital — correct slowly.

• Correct by >10 mmol/L in 24 h (osmotic demyelination)
• Give 0.9% saline to SIADH (can lower Na⁺ further)
• Fluid-restrict a hypovolaemic or post-SAH patient
• Start tolvaptan with fluid restriction or in liver disease

• Over-rapid correction
• Saline in SIADH
• Missing adrenal insufficiency
• Not testing urine before treating

HDU/ICU for severe symptoms; ward otherwise with 4–6-hourly Na⁺. Recheck Na⁺ 48–72 h after discharge.