Treatment of Mild to Moderate Hyponatraemia (Serum Sodium 120–135 mmol/L) with Euvolaemia or Hypervolaemia

Clinical Scenario

This protocol applies to patients with mild or moderate hyponatraemia — serum sodium in the range of 120–135 mmol/L — who present with euvolaemia or hypervolaemia. Determining the patient's volume status is the key step that defines which management pathway applies.

Severity Classification

Mild hyponatraemia: serum sodium 131–135 mmol/L. Moderate: 120–130 mmol/L. Severe: below 120 mmol/L. This protocol covers the mild and moderate range in euvolaemic or hypervolaemic patients.

Treatment Approach (partial — full regimen in protocol)

Management involves a targeted restriction strategy aimed at addressing the underlying volume and solute balance; the complete approach, monitoring parameters, and decision points are provided in the full protocol.

Key Correction Target

Correction must proceed slowly — generally no more than 8 mmol/L in any 24-hour period. Overly rapid correction carries significant risk.

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References

HYPOnatraemia (Mild: 135–131 mmol/L, Moderate: 130–120 mmol/L, Severe: less than 120 mmol/L)
If euvolaemic or hypervolaemic, consider potential causes such as medicines (SSRIs, diuretics, antiepileptics), conditions associated with inappropriate ADH secretion or reduced effective circulating volume (cirrhosis, cardiac failure). Manage with fluid restriction.
Correction should occur slowly – generally no more than 8 mmol/L in 24 hours.

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