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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NephrologyManagement
Hyponatremia Management Algorithm
Hyponatremia Management Algorithm: Hyponatraemia: Na+ under 135 mmol/L (adult) → Grade symptoms first, not the Na+ number → Severe symptoms: 3% NaCl 150...
Pathway Overview
18 steps
Algorithm Steps
18 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. Then follow the one matching step below.
- Severe symptoms: 3% NaCl boluses now, at any Na+ level (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
- These symptoms can have other causes: look for them too
03Action Severe symptoms: 3% NaCl 150 mL IV over 20 min now
Adults, acute or chronic hyponatraemia. Check bedside glucose first (seconds): high glucose (DKA or HHS) means use the corrected Na+ and the DKA or HHS pathway, not 3% NaCl. Give the bolus also in heart failure, cirrhosis or kidney failure. Send blood and urine samples, but do not wait for other results. Manage in HDU or ICU.
- Adult: 3% NaCl 150 mL IV over 20 min. Very 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 total
- 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. Na+ at 6 and 12 h, then daily
- 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 or low K+: still give the boluses. Then keep the total rise to 8 mmol/L in 24 h. Replacing K+ also raises Na+
04Action Moderately severe symptoms: one 3% NaCl 150 mL bolus
Adult: 3% NaCl 150 mL IV over 20 min, once. First check bedside glucose: DKA or HHS means no 3% NaCl. 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. Limit: 10 mmol/L in the first 24 h (8 mmol/L if high ODS risk)
- 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+ (for example thiazides). 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 Check serum osmolality and urine tests
Serum osmolality, glucose, urine osmolality and urine Na+ (urine taken at the same time as the blood). 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 such as beer or tea-and-toast diet). Na+ can rise fast once intake is corrected
- Urine osmolality above 100: urine Na+ 30 mmol/L or less suggests low effective volume; above 30 mmol/L: assess volume and diuretic use
07Decision Hypotonic hyponatraemia confirmed?
Yes: serum osmolality under 275 mOsm/kg, or no cause of non-hypotonic hyponatraemia found. Symptomatic treatment above does not wait for this answer.
- If Yes
08Warning Hypotonic: think of adrenal insufficiency before SIAD
Adrenal insufficiency can look like SIAD or like volume loss. Fluid restriction alone will not treat it.
- 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 (adult). Do not wait for the result
- After hydrocortisone, Na+ can rise fast: watch urine output and check Na+ often
09Warning 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): aim for 4 to 6 mmol/L per day and no more than 8 mmol/L in any 24 h.
- 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, or after water intake falls): 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 (0.5 mL of 4 microgram/mL; not more often than every 8 h)
10Action 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
11Action 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
12Action 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. After subarachnoid haemorrhage, do not restrict fluid: get neurosurgical or ICU advice. Tolvaptan is for specialists only (see below).
- 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. Stop drugs that cause SIAD (for example SSRIs, carbamazepine)
- 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. Urea is not TGA-registered: ask hospital pharmacy
- Tolvaptan: ESE advises against it for moderate or profound hyponatraemia. Specialist only; start in hospital at 15 mg orally once daily; check Na+ often. Not with 3% NaCl, in hypovolaemia, anuria, urgent need to raise Na+, inability to sense thirst, or with strong CYP3A inhibitors. Avoid in liver disease and pregnancy. No fluid restriction in the first 24 h. Max 30 days
- Low solute intake or polydipsia (urine osmolality 100 mOsm/kg or less): correct the intake; Na+ can rise fast
13Action Fluid overload (hypervolaemic): treat heart, liver or kidney disease
Heart failure, cirrhosis, nephrotic syndrome or kidney failure. Do not give 0.9% NaCl. The ESE guideline advises against vaptans here.
- 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 as its own guideline advises, for example loop diuretic for congestion
- Tolvaptan: avoid in liver disease, including cirrhosis (risk of liver injury)
14Action 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 boluses: Na+ after each bolus. During a continued 3% NaCl infusion: every 4 h. After severe symptoms improve: Na+ at 6 and 12 h, then daily until stable
- 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
15Action Before discharge: plan follow-up of the cause
Persistent hyponatraemia needs a clear plan for the cause, the drugs and the next Na+ check.
- Stop or replace the drug that caused it where possible (for example thiazide, SSRI, carbamazepine)
- On fluid restriction, urea or tolvaptan: plan the next Na+ check with the treating team
- After tolvaptan stops, restart fluid restriction and check Na+ and volume status
- Treat the cause (for example cancer, lung or brain disease, heart failure, cirrhosis)
16Outcome Goals: symptoms controlled, Na+ rise within 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 in any 24 h if high ODS risk). Target Na+ 130 mmol/L or more over days, not hours.
17End End of pathway
Reassess if symptoms or Na+ change.
If No18Outcome Not hypotonic: treat the cause, not the Na+
Hyperglycaemia: treat the glucose and use the corrected Na+. Pseudohyponatraemia (very high lipids or protein): confirm with direct ISE or a blood gas Na+. Mannitol, glycine or contrast: seek specialist advice.
- Path rejoins step 17Shared downstream outcome
Guideline Source
Spasovski G et al. Clinical practice guideline on diagnosis and treatment of hyponatraemia (ERA-EDTA/ESE/ESICM). Nephrol Dial Transplant 2014;29 Suppl 2:i1-i39
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; oral urea is not TGA-registered and access varies.
Contraindicated Populations
Neonates, children and adolescents (use a paediatric protocol with weight-based 3% NaCl)Patients on dialysis (nephrology advice)
Applicable Regions
AUEUUS
AU: Units are mmol/L as reported by Australian labs. Tolvaptan (Samsca and generics) is TGA-registered for hypervolaemic or euvolaemic hyponatraemia; start in hospital. Oral urea is not on the ARTG: ask hospital pharmacy. Check local stock and protocol for 3% NaCl.
Global: Based on the ERA-EDTA/ESE/ESICM 2014 guideline, with US expert panel 2013 limits for patients at high risk of osmotic demyelination.
Version 2Next review: 2027-09-30
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Frequently Asked Questions
What is the Hyponatremia Management Algorithm?
The Hyponatremia Management Algorithm is a management clinical algorithm for Nephrology. 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 (ERA-EDTA/ESE/ESICM). Nephrol Dial Transplant 2014;29 Suppl 2:i1-i39.
What guideline is the Hyponatremia Management Algorithm based on?
This algorithm is based on Spasovski G et al. Clinical practice guideline on diagnosis and treatment of hyponatraemia (ERA-EDTA/ESE/ESICM). Nephrol Dial Transplant 2014;29 Suppl 2:i1-i39 (DOI: 10.1093/ndt/gfu040).
What are the limitations of the Hyponatremia Management Algorithm?
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; oral urea is not TGA-registered and access varies.. Individual patient factors may require deviation from these recommendations.
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