# Hyponatraemia and SIADH in cancer: emergency hypertonic saline, safe correction and treating the cause

Source: https://onco.cc/protocols/hyponatraemia-siadh/  
OnCo record `hyponatraemia-siadh` (Protocol). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Low sodium in the blood is common in cancer, especially small-cell lung cancer, and can also come from some cancer drugs, sickness or diarrhoea. Vomiting, confusion, drowsiness or a fit with low sodium is an emergency: hospital teams give a strong salt drip in small doses and check often, because raising sodium too fast can damage the brain. Then the cause is treated.

## Summary

Treatment follows symptoms, not the number (Society for Endocrinology 2016): severe symptoms (vomiting, seizures, reduced consciousness, cardiorespiratory arrest) need immediate hypertonic saline whatever the cause, supervised by a senior clinician, aiming for a 5 mmol/L rise in the first hour; if limits of 10 mmol/L in 24 hours or 18 mmol/L in 48 hours are exceeded, hypertonic fluid stops and an experienced clinician considers hypotonic fluid, with or without an antidiuretic such as desmopressin, to re-lower. After the emergency, urine osmolality and urine sodium define the cause.

The Korean Society of Nephrology 2022 guideline suggests rapid intermittent boluses rather than slow continuous infusion (B, low), based on the SALSA trial (178 patients: overcorrection 17.2% against 24.2%, not significant; re-lowering treatment needed less often with boluses, 41.4% against 57.1%), and tabulates the European bolus regimen of 150 mL over 20 minutes repeated two to three times for severe symptoms; it notes the European guideline graded bolus therapy 1D. It sets a stricter limit of 8 mmol/L a day for people at high risk of osmotic demyelination. For SIAD it names fluid restriction as standard, with oral salt plus a loop diuretic, or a vaptan, second line; it suggests vaptans for moderate to severe hyponatraemia (B, low) where the European guideline recommends against them in people without moderately severe or severe symptoms. In people with brain disease, including brain tumours, it warns against fluid restriction because of volume depletion.

In cancer, SIADH is the usual cause, most often with small-cell lung cancer, from ectopic vasopressin or from anticancer and palliative drugs; vomiting and diarrhoea cause hypovolaemic hyponatraemia (The Oncologist 2012). A 2026 scoping review of 86 SCLC patients on tolvaptan reported an initial response in all cases and overcorrection in five.

## Fields

- Kind: Protocol
- Last checked: 2026-11-11
- Also known as: low sodium in cancer; SIADH; SIAD; syndrome of inappropriate antidiuretic hormone; paraneoplastic hyponatraemia; hypertonic saline bolus
- Tags: protocol; acute-oncology; oncological-emergency; electrolytes

## Connected records

- protocols: [Checkpoint inhibitor hypophysitis and adrenal insufficiency: emergency treatment, replacement and steroid emergency card](https://onco.cc/protocols/irae-hypophysitis-adrenal/)
- cancers: [Small-cell lung cancer](https://onco.cc/cancers/sclc/)

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