Hyponatraemia: Na+ under 135 mmol/L (adult)
Adults only. Children: use a paediatric protocol. If the result is unexpected, repeat Na+ with the same method and check glucose.
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Internal MedicineEmergency
Acute Hyponatremia Management - Hospitalist
Acute Hyponatremia Management - Hospitalist: Hyponatraemia: Na+ under 135 mmol/L (adult) → Grade symptoms first, not the Na+ number → Severe symptoms: 3...
Pathway Overview
14 steps
Algorithm Steps
14 total
01Start 02Action Grade symptoms first, not the Na+ number
Severe: vomiting, seizures, coma (GCS 8 or less), abnormal deep somnolence, cardiorespiratory distress. Moderately severe: nausea without vomiting, confusion, headache. Check bedside glucose first. Then follow the one matching step below.
- Severe symptoms: 3% NaCl boluses now (next step)
- Moderately severe symptoms: one 3% NaCl bolus
- No or mild symptoms: no hypertonic bolus, except an acute fall of more than 10 mmol/L
- Na+ 130 to 134 mmol/L: severe symptoms are rarely due to Na+ alone; look for another cause. At any Na+, look for other causes too
03Action Severe symptoms: 3% NaCl 150 mL IV over 20 min now
Adults, hypotonic hyponatraemia (acute or chronic). High glucose (for example HHS, DKA): use corrected Na+; if 135 mmol/L or more, no 3% NaCl, treat the hyperglycaemic crisis. Do not delay for other tests. Manage in HDU or ICU. Send serum and urine samples, but give the bolus first.
- Adult: 3% NaCl 150 mL IV over 20 min. Low body weight: consider 2 mL/kg per bolus (max 150 mL)
- Check Na+ after each bolus. Repeat 150 mL over 20 min until Na+ has risen 5 mmol/L: up to 3 boluses in the first hour
- Na+ up 5 mmol/L and symptoms better: stop 3% NaCl. Keep the line open with the smallest volume of 0.9% NaCl. Start cause-specific treatment
- Not better after a 5 mmol/L rise: continue 3% NaCl to raise Na+ 1 mmol/L per h. Stop when symptoms improve, Na+ has risen 10 mmol/L in total, or Na+ reaches 130 mmol/L. Check Na+ every 4 h. Look for another cause
- High risk of osmotic demyelination: still give the boluses. Then keep the total rise to 8 mmol/L in 24 h
04Action Moderately severe symptoms: one 3% NaCl 150 mL bolus
Adult: 3% NaCl 150 mL IV over 20 min, once. First check glucose: high glucose needs corrected Na+ (no 3% NaCl if 135 mmol/L or more). Start the cause work-up and cause-specific treatment at the same time.
- Aim for a Na+ rise of 5 mmol/L in 24 h
- Check Na+ at 1, 6 and 12 h
- Stop drugs and fluids that can lower Na+, if possible
- Na+ falls further: treat as severe symptoms. Symptoms do not improve as Na+ rises: look for another cause
05Action No or mild symptoms: no hypertonic bolus
Correct slowly and find the cause. Stop non-essential fluids and drugs that can lower Na+. This applies at any Na+ level, including under 125 mmol/L.
- Chronic (48 h or more, or duration unknown): no 3% NaCl bolus. Treat the cause
- Acute (under 48 h, for example after surgery, endurance exercise, MDMA or polydipsia) with a fall of more than 10 mmol/L: one 3% NaCl 150 mL IV over 20 min, then Na+ at 4 h
- Mild (130 to 134 mmol/L): do not treat only to raise the Na+ number
- Na+ under 130 mmol/L: check Na+ every 6 h until stable
06Action Confirm hypotonic hyponatraemia
Serum osmolality, glucose, urine osmolality and urine Na+ (same time as the blood sample). Also TSH, cortisol, creatinine, K+ and a drug review.
- Serum osmolality under 275 mOsm/kg: hypotonic hyponatraemia
- High glucose: add 2.4 mmol/L to Na+ for each 5.5 mmol/L of glucose above 5.5 mmol/L
- Normal or high osmolality: consider hyperglycaemia, mannitol, glycine (TURP), contrast, or pseudohyponatraemia (very high lipids or protein). High urea or alcohol raises measured osmolality but Na+ can still be hypotonic
- Urine osmolality 100 mOsm/kg or less: excess water intake (polydipsia, low solute intake)
- Urine osmolality above 100: urine Na+ 30 mmol/L or less suggests low effective volume; above 30 mmol/L: assess volume and diuretic use
07Warning Think of adrenal insufficiency before SIAD
Adrenal insufficiency can look like SIAD or like volume loss. Fluid restriction alone will not treat it. Low BP (adrenal crisis): also give 0.9% NaCl 1000 mL IV in the first hour (adult).
- Clues: low BP, high K+, low glucose, pituitary disease, recent or long-term steroid use
- Unwell or low BP: take cortisol, then give hydrocortisone 100 mg IV at once, then 50 mg IV 6-hourly (adult). Do not wait for the result
- After hydrocortisone, Na+ can rise fast: watch urine output and check Na+ often
08Warning Limit the Na+ rise: 10 mmol/L in first 24 h
Then 8 mmol/L per 24 h until Na+ reaches 130 mmol/L. High risk of osmotic demyelination (ODS): 8 mmol/L in any 24 h. Replacing K+ also raises Na+.
- High ODS risk: Na+ 105 mmol/L or less, low K+, alcohol use disorder, malnutrition, advanced liver disease
- Fast rise likely when urine output goes above 100 mL/h (after volume repair, hydrocortisone, stopping a thiazide or desmopressin, stopping excess water intake in polydipsia, or restoring food in low solute intake): check Na+ every 2 h
- Limit exceeded: stop active treatment. Get expert advice now on relowering Na+ with 5% glucose IV and desmopressin 2 microgram IV (not more often than every 8 h)
09Action Assess volume status, then follow the matching step
Clinical signs are often unreliable: use them with urine Na+, diuretic use and the history. If unsure and no fluid overload, a Na+ rise with 0.9% NaCl supports low volume; in SIAD it can lower Na+, so check Na+ during the trial.
- Low volume: dry mucosa, tachycardia, postural drop, urine Na+ usually 30 mmol/L or less (higher with diuretics, adrenal or renal salt loss)
- Normal volume: no oedema, no signs of volume loss, urine Na+ usually above 30 mmol/L
- Fluid overload: oedema, raised JVP, ascites
10Action Low volume (hypovolaemic): 0.9% NaCl or balanced crystalloid
Shock or haemodynamic instability: resuscitate now. This need overrides the Na+ correction limit. Not for SIAD or fluid overload: 0.9% NaCl can lower Na+ in SIAD.
- Stable adult: 0.9% NaCl or balanced crystalloid 0.5 to 1.0 mL/kg per h IV (max 1.0 mL/kg per h while stable; about 35 to 70 mL/h at 70 kg). Reassess often
- Causes: vomiting, diarrhoea, diuretics (thiazides), adrenal insufficiency, renal or cerebral salt loss
- Stop diuretics. Treat the cause
- Once volume is restored, urine output can rise suddenly and Na+ can rise fast: check Na+ every 2 h
11Action Normal volume (euvolaemic): likely SIAD, restrict fluid
First exclude adrenal insufficiency, hypothyroidism and diuretic use. Do not give 0.9% NaCl: in SIAD it can lower Na+ further. Stop drugs that cause SIAD. After subarachnoid haemorrhage: do not restrict fluid (risk of cerebral ischaemia); get neurosurgical or ICU advice.
- SIAD criteria: serum osmolality under 275 mOsm/kg, urine osmolality above 100 mOsm/kg, urine Na+ above 30 mmol/L, euvolaemia, no recent diuretic, normal thyroid, adrenal and kidney function
- First line: fluid restriction, usually 500 to 1000 mL/day (not after subarachnoid haemorrhage)
- Second line (with specialist): oral urea 15 to 30 g/day (ESE: 0.25 to 0.50 g/kg/day; US panel: max 60 g/day), or low-dose loop diuretic plus oral NaCl
- Tolvaptan: ESE does not recommend it for SIAD. Specialist only; start in hospital. Not with 3% NaCl, in hypovolaemia, anuria, urgent need to raise Na+, inability to sense or respond to thirst, or with strong CYP3A inhibitors; avoid in liver disease and pregnancy. No fluid restriction in the first 24 h
- Common causes: drugs (SSRIs, carbamazepine, opioids), lung and brain disease, cancer, pain, nausea, after surgery. Low solute intake or polydipsia: urine osmolality 100 mOsm/kg or less
12Action Fluid overload (hypervolaemic): treat heart, liver or kidney disease
Heart failure, cirrhosis, nephrotic syndrome or kidney failure. Do not give 0.9% NaCl. Do not use vaptans (ESE). Cirrhosis with Na+ under 125 mmol/L: stop diuretics and get hepatology advice.
- Mild or moderate Na+ (125 to 134 mmol/L): do not treat only to raise the Na+ number
- Fluid restriction to prevent more fluid overload
- Treat the underlying disease, for example loop diuretic for heart-failure congestion (not in cirrhosis with Na+ under 125 mmol/L)
- Tolvaptan: avoid in liver disease, including cirrhosis (risk of liver injury)
13Action Monitor Na+, urine output and K+
Check Na+ with the same method each time. Reassess the cause if Na+ does not respond.
- During 3% NaCl infusion: Na+ every 4 h. After severe symptoms improve: Na+ at 6 and 12 h, then daily until stable
- Moderately severe symptoms: Na+ at 1, 6 and 12 h
- Na+ under 130 mmol/L without severe symptoms: every 6 h until stable
- Urine output above 100 mL/h: Na+ every 2 h
- Na+ does not improve: review the diagnosis and ask an endocrinologist or nephrologist
14Outcome Goals of treatment
Severe symptoms controlled, Na+ rise within the limits, cause treated.
- Relieve severe symptoms with a 5 mmol/L rise
- Stay within 10 mmol/L in the first 24 h and 8 mmol/L per 24 h after (8 mmol/L if high ODS risk)
- Treat the cause and review drugs that lower Na+ (for example thiazides, SSRIs, carbamazepine)
- Target Na+ 130 mmol/L or more over days, not hours
Guideline Source
Spasovski G et al. Clinical practice guideline on diagnosis and treatment of hyponatraemia (ESE/ESICM/ERA-EDTA). Eur J Endocrinol 2014;170(3):G1-G47
Clinical Safety Information
Clinical Decision Support — Not a Substitute for Clinical Judgment
Individual patient factors may require deviation from these recommendations.
Known Limitations
- Adults only. Correction limits (10 mmol/L first 24 h; 8 mmol/L if high ODS risk) are expert consensus, and the safest limits are still debated.
- Volume status is hard to judge at the bedside; adrenal insufficiency, diuretics and several causes can coexist.
- Not for children, pregnancy-specific causes (for example pre-eclampsia) or dialysis patients: seek specialist advice.
- Tolvaptan and urea are specialist treatments; urea availability in Australia varies.
Contraindicated Populations
Children and adolescents (use a paediatric protocol)Patients on dialysis (nephrology advice)
Applicable Regions
AUEUUS
AU: Units are mmol/L as reported by Australian labs. Tolvaptan (Samsca) is TGA-registered for hypervolaemic or euvolaemic hyponatraemia; start in hospital. Check local stock and protocol for 3% NaCl.
Global: Based on the ESE/ESICM/ERA-EDTA 2014 guideline, with US expert panel 2013 limits for high-risk patients.
Version 2Next review: 2027-09-30
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Frequently Asked Questions
What is the Acute Hyponatremia Management - Hospitalist?
The Acute Hyponatremia Management - Hospitalist is a emergency clinical algorithm for Internal Medicine. It provides a structured decision tree to guide clinical decision-making, based on Spasovski G et al. Clinical practice guideline on diagnosis and treatment of hyponatraemia (ESE/ESICM/ERA-EDTA). Eur J Endocrinol 2014;170(3):G1-G47.
What guideline is the Acute Hyponatremia Management - Hospitalist based on?
This algorithm is based on Spasovski G et al. Clinical practice guideline on diagnosis and treatment of hyponatraemia (ESE/ESICM/ERA-EDTA). Eur J Endocrinol 2014;170(3):G1-G47 (DOI: 10.1530/EJE-13-1020).
What are the limitations of the Acute Hyponatremia Management - Hospitalist?
Known limitations include: Adults only. Correction limits (10 mmol/L first 24 h; 8 mmol/L if high ODS risk) are expert consensus, and the safest limits are still debated.; Volume status is hard to judge at the bedside; adrenal insufficiency, diuretics and several causes can coexist.; Not for children, pregnancy-specific causes (for example pre-eclampsia) or dialysis patients: seek specialist advice.; Tolvaptan and urea are specialist treatments; urea availability in Australia varies.. Individual patient factors may require deviation from these recommendations.
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