This protocol applies to patients with chronic hyponatraemia — confirmed to have been present for at least 48 hours — in the setting of syndrome of inappropriate antidiuresis (SIAD) with normal extracellular fluid volume, serum sodium below 135 mmol/l, and no severe or moderately severe symptoms.
SIAD is a diagnosis of exclusion. Confirming that hyponatraemia is chronic (present for at least 48 h) is a defining prerequisite for this pathway — the documented duration directly shapes the permissible management approach. Normal extracellular fluid volume and the absence of urgent symptoms place this case in a specific risk stratum with its own treatment priorities.
For moderate or profound hyponatraemia in this setting, management begins with a specific strategy around fluid intake. The structured protocol also identifies particular agents that carry explicit recommendations against their use in this context — distinctions that matter for safe, guideline-concordant care.