Treatment of Chronic Hyponatraemia (≥ 48 h, Serum Sodium < 135 mmol/l) with Contracted Extracellular Fluid Volume
This protocol covers patients with hyponatraemia confirmed to have been present for at least 48 hours, with serum sodium below 135 mmol/l and a reduced circulating extracellular fluid volume, in the absence of severe or moderately severe symptoms.
Clinical scenario
Chronic hyponatraemia — documented for at least 48 hours — combined with a contracted extracellular fluid volume. This pattern reflects a combined true sodium and water deficit. Severe or moderately severe neurological symptoms are not present.
Approach
The primary step is restoration of extracellular fluid volume through intravenous fluid administration. When haemodynamic instability is present, the management environment and monitoring requirements differ. The complete regimen — including fluid selection, infusion considerations, and monitoring parameters — is available in the full protocol.
Full details, including specific fluid choices and clinical monitoring guidance, are in the structured protocol below.
References
We define ‘chronic’ hyponatraemia as hyponatraemia that is documented to exist for at least 48 h.
Patients with hyponatraemia and a contracted extracellular fluid volume have a combination of a true sodium and water deficit.
We recommend restoring extracellular volume with i.v. infusion of 0.9% saline or a balanced crystalloid solution at 0.5–1.0 ml/kg per h (1B).
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