Hyponatraemia

Hyponatraemia (Na+ <135) is the commonest electrolyte disorder. Severity: mild 130–134, moderate 125–129, severe <125. Rate of correction matters most: chronic hyponatraemia corrected too fast causes osmotic demyelination syndrome (ODS). Acute…

Hyponatraemia Management

The pathway

1 · Assess severity & symptoms

Severe symptoms (seizures, coma, respiratory arrest) → treat immediately
Moderate (nausea, confusion, headache) → urgent management
Mild/asymptomatic → slower correction

2 · Determine chronicity

Acute (<48h): can correct at up to 2mmol/L/hr initially
Chronic (>48h or unknown): correction rate must not exceed 10mmol/L per 24h (max 18mmol/L per 48h) — ODS risk

3 · Identify cause

Hypovolaemic (diarrhoea, vomiting, Addison's): fluid depletion + urine Na+ <20
Euvolaemic (SIADH, hypothyroidism): exclude drugs
Hypervolaemic (HF, cirrhosis, nephrotic): dilutional

4 · Symptomatic / severe hyponatraemia

150ml 3% NaCl (hypertonic saline) over 20 minutes IV. Repeat up to 3 times or until symptoms improve. Target: Na+ rise of 5mmol/L initially, then re-evaluate.

5 · SIADH management

Fluid restriction 500–1000ml/day. Stop causative drugs. Demeclocycline or tolvaptan in refractory SIADH (specialist input required).

6 · Monitor correction rate

Na+ every 2–4 hours during active correction. If correcting too fast: slow or stop hypertonic saline, consider desmopressin (DDAVP) to re-lower Na+ (senior guidance).

Drugs

Drug	Dose	Route	Notes
3% NaCl (hypertonic saline)	150ml	IV	Over 20 minutes. For symptomatic/severe hyponatraemia. Repeat up to 3x.
0.9% NaCl	250ml–1L	IV	For hypovolaemic hyponatraemia. Do NOT use in euvolaemic/hypervolaemic.
Desmopressin (DDAVP)	1–2mcg	IV	Stops over-rapid correction. Senior guidance. Iatrogenic intervention.

When to escalate

Na+ <120 with symptoms (seizure, coma) — urgent hypertonic saline + HDU,Na+ rising >10mmol/L in 24h — risk of ODS, seek endocrine/nephrology,Na+ <125 with Addisonian crisis (postural hypotension, K+ raised) — hydrocortisone,Refractory hyponatraemia → nephrology/endocrinology review

Reference: European Clinical Practice Guidelines: Hyponatraemia 2014 (updated 2022)

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