This protocol applies to patients with syndrome of inappropriate antidiuretic hormone secretion (SIADH) presenting with severe hyponatraemia. When hyponatraemia causes severe symptoms, it reflects the presence of brain oedema — a situation requiring urgent, structured management beyond first-hour measures.
The initial approach for this presentation — first-hour management with prompt i.v. 3% hypertonic saline infusion, repeated to target a 5 mmol/l increase in serum sodium concentration within one hour sufficient to improve symptoms — did not meet its goals. Either the target sodium rise was not achieved, symptoms have not adequately improved, or both.
This protocol defines the structured next step after that first-hour management falls short.
The approach at this stage centres on continuing intravenous hypertonic saline, with the duration and continuation governed by close, timed monitoring of serum sodium concentration and defined stopping conditions based on clinical and biochemical response. In parallel, additional diagnostic evaluation is indicated to determine whether causes other than hyponatraemia are contributing to the persistent symptoms.
The complete regimen — including the precise targets, stopping thresholds, monitoring intervals, and diagnostic workup — is in the full protocol.
The goals of this next-line protocol are improvement of symptoms and a controlled, incremental rise in serum sodium concentration, with defined upper limits to guide safe cessation of therapy and prevent overcorrection.
DOI: 10.1530/EJE-13-1020
When hyponatraemia causes severe symptoms, it reflects the presence of brain oedema.
We recommend continuing an i.v. infusion of 3% hypertonic saline or equivalent aiming for an additional 1 mmol/l per h increase in serum sodium concentration (1D).
We recommend stopping the infusion of 3% hypertonic saline or equivalent when the symptoms improve, the serum sodium concentration increases 10 mmol/l in total or the serum sodium concentration reaches 130 mmol/l, whichever occurs first (1D).
We recommend additional diagnostic exploration for other causes of the symptoms than hyponatraemia (1D).
We suggest checking the serum sodium concentration every 4 h as long as an i.v. infusion of 3% hypertonic saline or equivalent is continued (2D).
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