Stethopedia | Approach

Approach to

Hyponatremia

Treat severe symptoms with 3% saline boluses first. Otherwise confirm hypotonicity, sort the cause by volume status and urine Osm/Na, and keep the rise ≤10 mmol/L in the first 24 h and ≤8 each day after.

  1. Serum Na <135 mmol/L, from no symptoms to seizure or coma
  2. Osm ≥275 mOsm/kg = not hypotonic: glucose (Na ↓2.4 per 5.6 mmol/L), lipids, paraprotein, glycine1,8
  3. Send urine Osm/Na, TSH, AM cortisol (never delay 3%); volume status; drugs1,9
  4. Severe symptoms, or acute with symptoms?

Severe symptoms: give 3% NaCl bolus now1,2,5,9

  • Seizure, coma, or somnolence1,4
  • Vomiting or cardiorespiratory distress1,4
  • Acute (<48 h) + symptoms: marathon, MDMA1
  • Symptoms resolve or Na ↑5: stop 3%1,9
  • Na rise over limit: relower, D5W ± DDAVP1,9

→ 3% NaCl 100–150 mL/10–20 min; Na after each; ≤3×; aim ↑4–61,2,9

If not: volume status + urine Osm/Na?

CausesCluesWorkupManagement

Hypovolemic

  • Vomiting, diarrhea, third-spacing
  • Thiazides; cerebral salt wasting
  • Primary adrenal insufficiency
  • Orthostatic, dry mucosa, low JVP
  • UNa ≤30: extrarenal loss1
  • UNa >30: diuretic, adrenal, renal1
  • Urine Na before giving fluids1
  • AM cortisol, K; ACTH stim if low
  • Isotonic saline; stop thiazide1
  • Adrenal crisis: IV hydrocortisone 100 mg9
  • UOP >100 mL/h: DDAVP ± D5W1,9

Euvolemic

  • SIADH: lung, CNS, cancer
  • Drugs: SSRIs, carbamazepine; pain
  • Low cortisol; severe hypothyroid
  • UOsm >100, UNa >30, no diuretic1
  • FE urate >12% even on diuretics7
  • Na falls after normal saline9
  • TSH, AM cortisol before SIADH label1
  • CXR; CT head if neuro signs
  • Fluid restrict 1–1.5 L/d; treat cause9
  • Urea 0.25–0.5 g/kg/d, or NaCl + loop1,3
  • Avoid normal saline in SIADH9

Hypervolemic

  • Heart failure
  • Cirrhosis
  • Nephrotic syndrome; advanced CKD
  • Edema, ascites, raised JVP
  • UNa ≤30 unless diuretics or CKD1
  • BNP, echo; liver tests, albumin
  • Creatinine, urine protein
  • Fluid restriction1
  • Loop diuretic if overloaded1
  • Treat the heart, liver or kidney

Low urine Osm

  • Primary polydipsia
  • Low solute: beer, tea and toast
  • UOsm ≤100 mOsm/kg1
  • Psychiatric illness; large intake
  • Beer, poor diet: high demyelination risk6
  • Diet and fluid intake history
  • UOsm ≈ last 2 digits of SG × 309
  • Restrict water; add solute slowly9
  • Corrects fast: watch Na and UOP6,9
  • DDAVP clamp if rising too fast9

Can't-miss cause Superscripts link to the references below.

References

  1. Spasovski G, Vanholder R, Allolio B, et al. Clinical practice guideline on diagnosis and treatment of hyponatraemia. Eur J Endocrinol. 2014;170:G1–G47. PubMed 24569125
  2. Verbalis JG, Goldsmith SR, Greenberg A, et al. Diagnosis, evaluation, and treatment of hyponatremia: expert panel recommendations. Am J Med. 2013;126(10 Suppl 1):S1–S42. PubMed 24074529
  3. Hoorn EJ, Zietse R. Diagnosis and treatment of hyponatremia: compilation of the guidelines. J Am Soc Nephrol. 2017;28:1340–1349. PubMed 28174217
  4. Adrogué HJ, Tucker BM, Madias NE. Diagnosis and management of hyponatremia: a review. JAMA. 2022;328:280–291. PubMed 35852524
  5. Baek SH, Jo YH, Ahn S, et al. Risk of overcorrection in rapid intermittent bolus vs slow continuous infusion therapies of hypertonic saline for patients with symptomatic hyponatremia: the SALSA randomized clinical trial. JAMA Intern Med. 2021;181:81–92. PubMed 33104189
  6. George JC, Zafar W, Bucaloiu ID, Chang AR. Risk factors and outcomes of rapid correction of severe hyponatremia. Clin J Am Soc Nephrol. 2018;13:984–992. PubMed 29871886
  7. Fenske W, Störk S, Koschker AC, et al. Value of fractional uric acid excretion in differential diagnosis of hyponatremic patients on diuretics. J Clin Endocrinol Metab. 2008;93:2991–2997. PubMed 18477658
  8. Hillier TA, Abbott RD, Barrett EJ. Hyponatremia: evaluating the correction factor for hyperglycemia. Am J Med. 1999;106:399–403. PubMed 10225241
  9. Gay E, Levy N, eds. Sodium Disorders; IV Fluids & Electrolyte Repletion; Adrenal Disorders. In: Department of Medicine Housestaff Manual, 30th ed. 2024:104, 107, 182.

For education only; not a substitute for clinical judgment or local protocols. Where sources differ, the flowchart follows the current guideline.

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