What is the management of hyponatremia?

Management of Hyponatremia

Initial Assessment and Classification

Hyponatremia is defined as serum sodium <135 mmol/L and should be further investigated when levels are <131 mmol/L. 1

Your initial workup must include:

• Serum and urine osmolality 1
• Urine sodium and electrolytes 1
• Serum uric acid 1
• Assessment of extracellular fluid volume status (hypovolemic, euvolemic, or hypervolemic) 1, 2

Volume status assessment is critical but imperfect—physical examination alone has only 41% sensitivity and 80% specificity. 1 Look specifically for:

• Hypovolemic signs: orthostatic hypotension, dry mucous membranes, decreased skin turgor, flat neck veins 1
• Hypervolemic signs: peripheral edema, ascites, jugular venous distention, pulmonary congestion 1, 2
• Euvolemic: absence of both hypovolemic and hypervolemic signs 1

Treatment Based on Symptom Severity

Severe Symptomatic Hyponatremia (Seizures, Coma, Altered Mental Status)

For severe symptomatic hyponatremia, immediately administer 3% hypertonic saline with an initial goal to correct 6 mmol/L over 6 hours or until severe symptoms resolve. 1, 2

• Administer 100 mL boluses of 3% saline over 10 minutes, repeatable up to three times at 10-minute intervals until symptoms improve 1
• The total correction must not exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome 1, 2, 3
• Monitor serum sodium every 2 hours during initial correction 1, 2
• Consider ICU admission for close monitoring 1

Calculate sodium deficit using: Desired increase in Na (mEq/L) × (0.5 × ideal body weight in kg) 1, 2

Mild to Moderate Symptomatic or Asymptomatic Hyponatremia

Treatment depends on volume status and underlying etiology, with slower correction rates appropriate. 1, 2

Treatment Based on Volume Status

Hypovolemic Hyponatremia

Discontinue diuretics and administer isotonic saline (0.9% NaCl) for volume repletion. 1, 2

• Urine sodium <30 mmol/L predicts good response to saline infusion (71-100% positive predictive value) 1, 2
• Once euvolemic, reassess and adjust management based on sodium response 1
• Correction rate should not exceed 8 mmol/L in 24 hours 1, 2

Euvolemic Hyponatremia (SIADH)

Fluid restriction to 1 L/day is the cornerstone of treatment for SIADH. 1, 2

• If no response to fluid restriction, add oral sodium chloride 100 mEq three times daily 1, 2
• For resistant cases, consider pharmacological options: urea, diuretics, lithium, or demeclocycline 1, 2
• Vaptans (tolvaptan 15 mg once daily, titrated to 30-60 mg) may be considered for clinically significant hyponatremia resistant to fluid restriction 1, 4
• For severe symptoms despite euvolemia, use 3% hypertonic saline with careful monitoring 1

SIADH diagnostic criteria: 1, 2

• Hypotonic hyponatremia with serum osmolality <275 mOsm/kg
• Inappropriate urine concentration (urine osmolality >100 mOsm/kg)
• Urine sodium >20-40 mmol/L
• Euvolemic state on clinical examination
• Normal thyroid, adrenal, and renal function

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

Implement fluid restriction to 1-1.5 L/day for serum sodium <125 mmol/L. 1, 2

• Discontinue diuretics temporarily if sodium <125 mmol/L 1, 2
• In cirrhotic patients, consider albumin infusion alongside fluid restriction 1, 2
• Avoid hypertonic saline unless life-threatening symptoms are present, as it may worsen edema and ascites 1, 2
• Sodium restriction (not fluid restriction) results in weight loss as fluid passively follows sodium 1, 2
• Vaptans may be considered for persistent severe hyponatremia despite fluid restriction and maximization of guideline-directed medical therapy, but use with extreme caution in cirrhosis due to higher risk of gastrointestinal bleeding (10% vs 2% placebo) 1, 4

Special Considerations for Neurosurgical Patients

Cerebral Salt Wasting (CSW) vs SIADH

Distinguishing CSW from SIADH is critical because treatment approaches are opposite. 1, 2

CSW characteristics: 1, 2

• True hypovolemia with CVP <6 cm H₂O
• Urine sodium >20 mmol/L despite volume depletion
• Evidence of extracellular volume depletion (hypotension, tachycardia, dry mucous membranes)
• More common in poor clinical grade, ruptured anterior communicating artery aneurysms, and hydrocephalus

CSW treatment—volume and sodium replacement, NOT fluid restriction: 1, 2

• Isotonic or hypertonic saline based on severity
• For severe symptoms: 3% hypertonic saline plus fludrocortisone (0.1-0.2 mg daily) in ICU 1, 2
• Hydrocortisone may be used to prevent natriuresis in subarachnoid hemorrhage patients 1, 2
• Never use fluid restriction in CSW—this worsens outcomes 1, 2

In subarachnoid hemorrhage patients at risk of vasospasm: 1, 2

• Do not treat with fluid restriction
• Consider fludrocortisone to prevent vasospasm
• Hypertonic saline increases regional cerebral blood flow and brain tissue oxygen

Critical Correction Rate Guidelines

The maximum correction rate should not exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome. 1, 2, 3

High-Risk Populations Requiring Slower Correction (4-6 mmol/L per day):

• Advanced liver disease 1, 2
• Alcoholism 1, 2
• Malnutrition 1, 2
• Prior encephalopathy 1, 2
• Severe hyponatremia (<120 mmol/L) 1, 2
• Hypophosphatemia, hypokalemia, hypoglycemia 1

Management of Overcorrection

If sodium correction exceeds 8 mmol/L in 24 hours: 1, 2

• Immediately discontinue current fluids and switch to D5W (5% dextrose in water)
• Consider administering desmopressin to slow or reverse the rapid rise
• Target reduction to bring total 24-hour correction to no more than 8 mmol/L from starting point

Watch for signs of osmotic demyelination syndrome (typically occurring 2-7 days after rapid correction): 1, 2

• Dysarthria
• Dysphagia
• Oculomotor dysfunction
• Quadriparesis

Monitoring Protocols

Severe symptoms: Monitor serum sodium every 2 hours during initial correction 1, 2

After resolution of severe symptoms: Monitor every 4 hours 1, 2

Mild symptoms or asymptomatic: Monitor every 24 hours initially, then adjust based on response 1, 2

Common Pitfalls to Avoid

• Overly rapid correction of chronic hyponatremia (>8 mmol/L in 24 hours) leading to osmotic demyelination syndrome 1, 2, 3
• Using fluid restriction in CSW, which worsens outcomes 1, 2
• Inadequate monitoring during active correction 1, 2
• Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms 1, 2
• Failing to recognize and treat the underlying cause 1, 2
• Ignoring mild hyponatremia (130-135 mmol/L) as clinically insignificant—it increases fall risk (23.8% vs 16.4%) and mortality 1, 3
• Using lactated Ringer's solution for hyponatremia treatment due to its hypotonic nature (130 mEq/L sodium, 273 mOsm/L) 1

Pharmacological Considerations

Vaptans (Vasopressin Receptor Antagonists)

Tolvaptan is FDA-approved for euvolemic and hypervolemic hyponatremia. 4

• Starting dose: 15 mg once daily, titrate to 30-60 mg based on response 1, 4
• Avoid fluid restriction during first 24 hours to prevent overly rapid correction 4
• Monitor closely to avoid overcorrection (>8 mmol/L/day) 1, 4
• Contraindicated with strong CYP3A inhibitors (ketoconazole increases tolvaptan AUC 5.4-fold) 4
• Use with extreme caution in cirrhosis due to 10% risk of gastrointestinal bleeding vs 2% with placebo 1, 4
• Common side effects: thirst, dry mouth, polyuria, nausea 4
• Risk of hypernatremia (1.7% vs 0.8% placebo) and osmotic demyelination syndrome 4