SIADH in the Hospitalized Patient: Master the Evidence-Based Diagnosis and Safe Management of Hyponatremia (Urea vs. Vaptans)

In this episode of Hospital Medicine Unplugged, we dive into Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH)—diagnose it early, treat fluid imbalances, and carefully manage hyponatremia.

We start with the essentials: identify and treat reversible causes first. Whether it’s medications, malignancy, or pulmonary/CNS disorders, addressing the underlying issue is key. For life-threatening symptoms like seizures or coma, 3% sodium chloride is recommended to quickly reverse cerebral edema, followed by specialist consultation.

For nonemergent cases, fluid restriction remains the first-line therapy—typically 1–1.5 liters/day. However, randomized trials show modest benefits. If that doesn't work, consider oral urea (15 g twice daily) for safe, effective treatment. Salt tablets + furosemide can also be used, but they have modest benefits and come with a higher risk of acute kidney injury and hypokalemia, so use cautiously in patients with comorbidities.

Next, we cover long-term management with Tolvaptan—a vasopressin receptor antagonist that’s highly effective but comes with monitoring challenges. Cost and monitoring requirements are limiting factors, so use it for refractory cases when other options fail.

Emerging therapies are on the horizon: SGLT2 inhibitors (e.g., empagliflozin) show promise, but the data are still limited.

Throughout all treatments, close monitoring of serum sodium is essential to avoid rapid correction and dangerous neurologic complications.

We wrap up with key pearls for monitoring during therapy:

• For severe hyponatremia (e.g., <120 mmol/L), monitor serum sodium every 6-8 hours.

• Tolvaptan and oral urea require daily sodium checks until stable, then less frequently.

• Always monitor for overcorrection to avoid osmotic demyelination—never correct more than 10 mmol/L in 24 hours.

Hospital-specific pearls: • Address reversible causes immediately (discontinue offending medications, treat underlying malignancy or CNS issues). • Fluid restriction is your starting point, but keep the fluid volume under 1.5 L/day. • If oral urea or salt + furosemide don’t work, move to Tolvaptan. • Close sodium monitoring is critical—check every 6–8 hours during active correction. • For severe cases, use 3% sodium chloride but stick to correction limits to avoid neurologic complications.

In summary: identify the cause, titrate fluid intake, and monitor sodium levels carefully—SIADH treatment requires precision and diligence to avoid long-term complications like cognitive impairment and fractures.

System moves: A SIADH management bundle that:

1. Auto-calculates fluid restriction in the EHR based on patient labs.

2. Orders 3% saline for symptomatic cases.

3. Flags Tolvaptan for refractory cases with specialist input.

4. Sets sodium monitoring schedules for ongoing management.

5. Triggers automatic alerts for SGLT2 inhibitors when appropriate, based on evolving evidence.

Managing SIADH requires careful attention to fluid balance, serum sodium, and patient-specific needs—get it right and you’ll prevent neurological complications while improving long-term outcomes.