Severe symptomatic hyponatraemia (seizure, reduced GCS, focal neurology) is an emergency needing hypertonic saline. Do not correct faster than 10 mmol/L in 24 h (8 if high risk) to avoid osmotic demyelination.
Severity and symptoms
- Mild: often asymptomatic; check if chronic
- Moderate: nausea, headache, confusion
- Severe: seizures, coma; correlate with rate of fall
- Acute (<48 h) vs chronic: guides urgency of correction
Initial tests
- Plasma Na+, glucose, urea, creatinine
- Serum osmolality, urine osmolality and Na+
- Consider TFTs, cortisol if appropriate
- Medicines: thiazides, SSRIs, carbamazepine, PPIs
Mild: 130 to 134
- Often chronic and asymptomatic
- Find and treat the cause
- No hypertonic saline
Moderate: 125 to 129
- Nausea, headache, confusion
- Cautious correction, treat the cause
- Fluid restrict if SIADH
Severe symptoms (any Na)
- Seizures, GCS drop, vomiting
- 150 mL of 2.7% saline over 10 to 20 min
- Target rise about 5 mmol/L then stop
Practical approach
1
1. Resuscitate
ABC, IV access, treat seizures per local protocol. If hyperglycaemia, correct Na for glucose (add ~2.4 mmol/L per 5 mmol/L glucose rise above normal, approximate).
ABC, IV access, treat seizures per local protocol. If hyperglycaemia, correct Na for glucose (add ~2.4 mmol/L per 5 mmol/L glucose rise above normal, approximate).
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2
2. Volume status
Hypovolaemic: 0.9% saline. Euvolaemic (SIADH likely): fluid restrict (often 750 to 1000 mL/24 h). Hypervolaemic (heart failure, cirrhosis): treat cause, restrict salt and water.
Hypovolaemic: 0.9% saline. Euvolaemic (SIADH likely): fluid restrict (often 750 to 1000 mL/24 h). Hypervolaemic (heart failure, cirrhosis): treat cause, restrict salt and water.
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3
3. Hypertonic saline
Severe symptomatic only, under senior care: 150 mL of 2.7% saline over 10 to 20 min, repeat to a target rise of about 5 mmol/L to stop symptoms, then stop. Check Na frequently.
Severe symptomatic only, under senior care: 150 mL of 2.7% saline over 10 to 20 min, repeat to a target rise of about 5 mmol/L to stop symptoms, then stop. Check Na frequently.
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4
4. Treat cause
Stop offending drugs. Manage SIADH (treat trigger, fluid restrict; vaptans or demeclocycline only under specialist care). Replace cortisol if adrenal insufficiency; treat hypothyroidism.
Stop offending drugs. Manage SIADH (treat trigger, fluid restrict; vaptans or demeclocycline only under specialist care). Replace cortisol if adrenal insufficiency; treat hypothyroidism.
| Situation | Maximum rise in Na |
|---|---|
| Standard | 10 mmol/L in 24 h and 18 in 48 h |
| High risk (chronic, hypokalaemia, liver disease, malnutrition) | 8 mmol/L in 24 h |
| If overcorrecting | Stop, give 5% dextrose, consider desmopressin (senior) |
SIADH clues
- Euvolaemic with inappropriately concentrated urine (osmolality over 100)
- Urine Na+ often over 30 mmol/L once diuretics excluded
- Normal thyroid and adrenal function; low uric acid supports it
Pitfalls
- Overcorrecting chronic hyponatraemia
- Large IV fluids in SIADH without restriction
- Missing pseudohyponatraemia (high glucose, lipids, paraprotein)
- Missing adrenal or hypothyroid cause
MedPrep - www.medprep.uk - Educational revision aid only. Not clinical guidance. Doses are adult examples; check the BNF, current guidelines and local policy, and seek senior advice. Nov 2026