Objectives: To synthesize current recommendations for hypotonic hyponatremia in adults, focusing on the SIADH and heart-failure contexts, compare them with real-world practice, and identify evidence gaps.
Search methods: A structured narrative review, not fully following the PRISMA framework. PubMed/MEDLINE and the Cochrane Library were searched (January 2012-July 2026) using three keyword blocks: hyponatremia/guideline; SIADH/fluid restriction/tolvaptan; sodium correction rate/osmotic demyelination. Of 13 records identified, 8 were retained after duplicate removal and screening, and synthesized narratively.
Results: Classification by extracellular fluid volume remains the diagnostic foundation, but clinical assessment alone has limited sensitivity and specificity (50-80% and 30-50%), making urine osmolality/sodium and fractional excretion of urate valuable adjuncts. The 2013 US and 2014 European guidelines agree on hypertonic saline for acute cases and limiting correction to around 8-10 mmol/L/24h, but differ in bolus dosing and the place of vaptans. In practice, fluid restriction, despite being the most common measure (44%), left only 19% of patients reaching Na⁺ ≥ 135 mmol/L at discharge.
Conclusion: Management of hyponatremia requires a high degree of individualization based on pathophysiology. Substantial gaps persist among guidelines and between guidelines and practice, warranting priority in future research.