Suspected SIADH (adult)
Low serum Na with low serum osmolality in a clinically euvolaemic adult. Not for children.
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EndocrinologyManagement
SIADH Diagnosis and Management
SIADH Diagnosis and Management: Suspected SIADH (adult) → Read first: children, aneurysmal SAH, high ODS risk → Severe symptoms? → Confirm SIADH: all es...
Pathway Overview
21 steps
Algorithm Steps
21 total
01Start 02Warning Read first: children, aneurysmal SAH, high ODS risk
These patients need a different plan in the steps below.
- Child: do not use this pathway. Adult 3% saline doses can overdose a child. Use a paediatric protocol.
- Aneurysmal SAH or recent neurosurgery: do not fluid restrict. Hypovolaemia can cause cerebral ischaemia. Get neurocritical care advice.
- High ODS risk (Na 105 mmol/L or less, alcohol use disorder, malnutrition, low K+, liver disease): limit Na rise to 8 mmol/L in any 24 h.
03Decision Severe symptoms?
Vomiting, cardiorespiratory distress, deep somnolence, seizures or coma (GCS 8 or less). Treat before the cause is known.
- If Yes
04Action Severe symptoms: adult 3% saline bolus now
Manage in HDU or ICU. Then confirm SIADH and treat the cause. Monitoring and over-correction steps below apply.
- Adult: 3% NaCl 150 mL IV over 20 min (very low body weight: 2 mL/kg, max 150 mL)
- Check Na at 20 min and give a further 150 mL 3% NaCl over 20 min
- Repeat until Na has risen 5 mmol/L (up to 3 boluses in the first hour)
- Limit rise: 10 mmol/L in first 24 h, then 8 mmol/L per 24 h (8 mmol/L in any 24 h if high ODS risk)
- Better after 5 mmol/L rise: stop 3% NaCl; keep IV line open with the smallest volume of 0.9% NaCl; check Na at 6 h, 12 h, then daily
- Not better: continue 3% NaCl to raise Na 1 mmol/L per hour; stop at symptom relief, 10 mmol/L total rise or Na 130 mmol/L; check Na every 4 h; look for other causes
If No05Decision Moderately severe symptoms?
Nausea without vomiting, confusion or headache.
- If Yes
06Action Moderately severe symptoms: one adult 3% saline bolus
Start tests and cause-specific treatment at the same time. Then confirm SIADH. Monitoring and over-correction steps below apply.
- Adult: 3% NaCl 150 mL IV over 20 min (very low body weight: 2 mL/kg, max 150 mL), once
- Aim for a Na rise of 5 mmol/L in 24 h
- Limit rise: 10 mmol/L in first 24 h, then 8 mmol/L per 24 h (8 mmol/L in any 24 h if high ODS risk)
- Check Na at 1 h, 6 h and 12 h
- Stop drugs that can cause hyponatraemia. Symptoms persist: look for other causes
If No07Action No or mild symptoms: usually no hypertonic saline
Confirm SIADH and treat the cause (steps below). Do not raise Na fast.
- Fall in Na documented within 48 h and more than 10 mmol/L: consider one 150 mL 3% NaCl bolus over 20 min (adult; very low body weight: 2 mL/kg, max 150 mL); check Na at 4 h
- Stop non-essential fluids and drugs that can cause hyponatraemia
- All patients: then confirm SIADH
08Action Confirm SIADH: all essential criteria
Take serum and urine samples at the same time, before treatment if possible.
- Effective serum osmolality below 275 mOsm/kg
- Urine osmolality above 100 mOsm/kg
- Clinically euvolaemic
- Urine Na above 30 mmol/L with normal salt and water intake
- No adrenal, thyroid, pituitary or renal insufficiency, and no recent diuretic use
- Supports SIADH: serum urate below 0.24 mmol/L, serum urea below 3.6 mmol/L
09Decision Another cause found?
Check TSH, cortisol, creatinine, diuretic use, volume status. Urine osmolality 100 mOsm/kg or less means excess water or low solute intake.
- If Yes
10Outcome Another cause found: not SIADH
Treat that cause (for example hypovolaemia, hypothyroidism, adrenal insufficiency, diuretics). Then follow the Monitoring and over-correction steps below.
If No11Action SIADH confirmed: find and treat the cause
Treating the cause is the main treatment.
- Drugs: stop if possible (for example SSRIs and other antidepressants, carbamazepine, oxcarbazepine, antipsychotics, cyclophosphamide, vincristine, NSAIDs, opiates)
- Lung: pneumonia, TB, positive-pressure ventilation
- CNS: stroke, SAH, meningitis, head injury, tumour
- Cancer: small cell lung cancer and others
- Other: pain, nausea, after surgery; idiopathic (often older adults)
- Na can rise fast when the cause is removed: see Monitoring
12Action Na below 130 mmol/L: fluid restriction first (not in aneurysmal SAH)
First line for moderate (125-129 mmol/L) or profound (below 125 mmol/L) SIADH. Mild (130-135 mmol/L): treat the cause only.
- Aneurysmal SAH or recent neurosurgery: do not restrict; keep euvolaemia; neurocritical care advice (hypertonic saline or fludrocortisone are options)
- Restrict all fluid (oral and IV) to about 500 mL/day below the 24 h urine output
- Unlikely to work if urine osmolality above 500 mOsm/kg or urine (Na + K) above serum Na
- Na rise less than 2 mmol/L per day after 24-48 h: add second-line treatment
- Do not give 0.9% saline to raise Na in SIADH: it can lower Na further when urine osmolality is high
13Action Fluid restriction not enough: urea, or loop diuretic plus salt
ESE 2014 second line. The two options are equal.
- Adult: oral urea 0.25-0.50 g/kg per day (max 0.50 g/kg per day). Australia: the hospital pharmacy may need to compound it
- Or: low-dose loop diuretic (for example furosemide) plus oral NaCl. Dose: specialist advice
- Do not use demeclocycline or lithium (ESE 2014 recommends against; kidney injury)
- Check Na, K+ and creatinine
14Warning Before tolvaptan: not if hypovolaemic, liver disease, urgent need, on 3% saline
Tolvaptan can raise Na too fast and can injure the liver. Avoid moderate CYP3A inhibitors (for example diltiazem, verapamil, fluconazole, erythromycin) and grapefruit juice: they raise tolvaptan levels.
- Contraindicated: hypovolaemic hyponatraemia, urgent need to raise Na, anuria, cannot sense or respond to thirst, strong CYP3A inhibitors (for example ketoconazole), allergy to tolvaptan or benzazepines
- Liver injury: use for 30 days at most; avoid in liver disease, including cirrhosis
- Do not fluid restrict in the first 24 h. Do not give with 3% saline
15Action Refractory SIADH: tolvaptan (specialist only, start in hospital)
ESE 2014 does not recommend vaptans in moderate and recommends against them in profound hyponatraemia. TGA indication: Na below 125 mmol/L, or milder hyponatraemia that causes symptoms and has not responded to fluid restriction. Pregnancy: avoid unless benefit clearly outweighs risk; stop breastfeeding. Then follow the Monitoring steps below.
- Adult: tolvaptan 15 mg orally once daily
- Increase to 30 mg, then 60 mg, at intervals of 24 h or more if needed. Max 60 mg daily
- Start and restart in hospital. Check Na and volume status often at start and after each dose increase
- K+ above 5 mmol/L or on drugs that raise K+: check K+ after starting
- Na rises too fast: stop or pause tolvaptan; consider hypotonic fluid
- Stop by 30 days. After stopping, resume fluid restriction and check Na
- On a CYP3A inducer (for example rifampicin, phenytoin, carbamazepine): tolvaptan may not work at the usual dose. On a P-gp inhibitor (for example ciclosporin): a lower dose may be needed
- All patients: monitor Na
16Action Monitoring and Na rise limits (all patients)
Prevent osmotic demyelination syndrome (ODS).
- Limit rise: 10 mmol/L in first 24 h, then 8 mmol/L per 24 h until Na 130 mmol/L
- High ODS risk (Na 105 mmol/L or less, alcohol use disorder, malnutrition, low K+, liver disease): 8 mmol/L in any 24 h
- Check Na every 6 h until stable (every 4 h while 3% NaCl continues)
- Urine output suddenly above 100 mL/h (water diuresis): check Na every 2 h
- Correcting low K+ also raises Na
- Strict fluid balance and neurological checks
17Decision Na rise above the limit?
More than 10 mmol/L in the first 24 h, or more than 8 mmol/L in any later 24 h. High ODS risk: more than 8 mmol/L in any 24 h.
- If Yes
18Action Over-correction: stop treatment and re-lower Na
Act now. Get expert advice. Then continue monitoring.
- Stop 3% NaCl, urea, salt, loop diuretic or tolvaptan
- With expert advice: 5% glucose 10 mL/kg IV over 1 h (adult), with strict urine output and fluid balance
- With expert advice: desmopressin 2 micrograms IV; do not repeat more often than every 8 h
- Australia: desmopressin injection comes as 4 micrograms/mL (Minirin) and 15 micrograms/mL (Octostim). Check the ampoule strength
If No19Decision Na stable and cause resolved?
Judge at review, not in the first days.
- If Yes
20Outcome Resolved: Na stable and cause treated
Stop SIADH treatment step by step and recheck Na.
If No21Outcome Chronic SIADH: long-term plan
Continue fluid restriction. Add urea, or loop diuretic plus salt, if needed. Check Na regularly. Tolvaptan only with specialist input, for 30 days at most.
Guideline Source
ESE/ESICM/ERA-EDTA Clinical Practice Guideline on Diagnosis and Treatment of Hyponatraemia (Spasovski et al., 2014)
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. Children need a paediatric hyponatraemia protocol.
- Aneurysmal SAH or recent neurosurgery: do not fluid restrict; get neurocritical care advice.
- SIADH is a diagnosis of exclusion: rule out hypovolaemia, hypothyroidism, adrenal insufficiency and diuretic use.
- Tolvaptan: specialist use only, 30 days at most; ESE 2014 does not recommend vaptans for moderate or profound hyponatraemia.
Contraindicated Populations
Children (use a paediatric hyponatraemia protocol)
Applicable Regions
AUUSEU
AU: Tolvaptan (SAMSCA 15 mg and 30 mg tablets) is on the ARTG. Conivaptan and demeclocycline are not. Oral urea may need hospital pharmacy compounding. Desmopressin injection: 4 micrograms/mL (Minirin) and 15 micrograms/mL (Octostim).
EU: ESE/ESICM/ERA-EDTA 2014: fluid restriction first; urea or loop diuretic plus oral NaCl second; vaptans not recommended for moderate or profound hyponatraemia.
US: US expert panel (Verbalis et al., Am J Med 2013) supports tolvaptan for selected patients. FDA: tolvaptan for 30 days at most; avoid in liver disease.
Version 2Next review: 2027-09-30
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Frequently Asked Questions
What is the SIADH Diagnosis and Management?
The SIADH Diagnosis and Management is a management clinical algorithm for Endocrinology. It provides a structured decision tree to guide clinical decision-making, based on ESE/ESICM/ERA-EDTA Clinical Practice Guideline on Diagnosis and Treatment of Hyponatraemia (Spasovski et al., 2014).
What guideline is the SIADH Diagnosis and Management based on?
This algorithm is based on ESE/ESICM/ERA-EDTA Clinical Practice Guideline on Diagnosis and Treatment of Hyponatraemia (Spasovski et al., 2014) (DOI: 10.1530/EJE-13-1020).
What are the limitations of the SIADH Diagnosis and Management?
Known limitations include: Adults only. Children need a paediatric hyponatraemia protocol.; Aneurysmal SAH or recent neurosurgery: do not fluid restrict; get neurocritical care advice.; SIADH is a diagnosis of exclusion: rule out hypovolaemia, hypothyroidism, adrenal insufficiency and diuretic use.; Tolvaptan: specialist use only, 30 days at most; ESE 2014 does not recommend vaptans for moderate or profound hyponatraemia.. Individual patient factors may require deviation from these recommendations.
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