Hyponatraemia

Act now

1. 1

   Severe symptoms: 150 mL of 3% (or equivalent 2.7%) sodium chloride IV over 20 minutes with senior/critical care input; recheck Na⁺ and repeat up to twice or until Na⁺ has risen 5 mmol/L.

3. 2

   Stop hypotonic fluids and offending drugs.

Assess

• Symptoms: severe (vomiting, seizures, GCS ≤8, cardiorespiratory distress), moderately severe (nausea without vomiting, confusion, headache), mild or none.
• Acute (<48 h) or chronic? Fluid status: hypovolaemic, euvolaemic, hypervolaemic.
• Drugs: thiazides, SSRIs, carbamazepine, PPIs, desmopressin, hypotonic IV fluids.

Investigations

• Paired serum and urine osmolality, urine sodium (before treatment where possible), glucose, U&E, TFTs, 9 am cortisol (or random if unwell), lipids/protein if pseudohyponatraemia possible.

Manage

• After a 5 mmol/L rise with improved symptoms: stop hypertonic saline, keep line open, start cause-specific treatment.
• Hypovolaemic: 0.9% sodium chloride. SIADH: fluid restriction. Hypervolaemic: treat the underlying heart, liver or kidney failure.
• Check Na⁺ at least 6-hourly in the first 24 hours of active correction; if overcorrecting, seek expert advice urgently.

Escalate when