How to manage a patient with hyponatremia?

Management of Hyponatremia

Hyponatremia (serum sodium <135 mmol/L) requires immediate assessment of symptom severity, volume status, and correction rate limits to prevent both neurologic complications from the hyponatremia itself and osmotic demyelination syndrome from overly rapid correction.

Initial Assessment and Classification

Determine symptom severity first, as this dictates urgency of treatment:

• Severe symptoms (seizures, coma, altered mental status, respiratory distress) constitute a medical emergency requiring immediate hypertonic saline 1
• Moderate symptoms include nausea, vomiting, confusion, headache, and require prompt but measured correction 1, 2
• Mild/asymptomatic cases allow for more conservative management focused on treating underlying causes 1

Assess volume status through physical examination (though sensitivity is only 41.1% and specificity 80%) 1:

• Hypovolemic signs: orthostatic hypotension, dry mucous membranes, decreased skin turgor, flat neck veins 1
• Euvolemic: no edema, normal blood pressure, normal skin turgor 1
• Hypervolemic signs: peripheral edema, ascites, jugular venous distention, pulmonary congestion 1

Obtain essential laboratory tests 1:

• Serum and urine osmolality
• Urine sodium and electrolytes
• Serum uric acid (level <4 mg/dL has 73-100% positive predictive value for SIADH) 1
• Thyroid function (TSH) and cortisol to exclude endocrine causes 1

Critical Correction Rate Guidelines

The single most important safety principle: NEVER exceed 8 mmol/L correction in 24 hours for chronic hyponatremia (>48 hours duration) to prevent osmotic demyelination syndrome 1, 3, 4.

For high-risk patients (advanced liver disease, alcoholism, malnutrition, severe hyponatremia <120 mmol/L), limit correction to 4-6 mmol/L per day, maximum 8 mmol/L in 24 hours 1, 5.

For acute hyponatremia (<48 hours), more rapid initial correction is safer, but still respect the 24-hour limit 1, 5.

Treatment Based on Symptom Severity

Severe Symptomatic Hyponatremia (Medical Emergency)

Administer 3% hypertonic saline immediately 1, 4, 6:

• Give 100 mL bolus over 10 minutes, can repeat up to 3 times at 10-minute intervals 1
• Target: correct 6 mmol/L over first 6 hours OR until severe symptoms resolve 1, 7
• Maximum total correction: 8 mmol/L in 24 hours 1, 3
• Monitor serum sodium every 2 hours during initial correction 1
• ICU admission for close monitoring 1

Mild to Moderate Symptomatic or Asymptomatic Hyponatremia

Treatment depends on volume status:

Hypovolemic Hyponatremia:

• Discontinue diuretics immediately 1
• Administer isotonic saline (0.9% NaCl) for volume repletion 1, 6
• Initial rate: 15-20 mL/kg/h, then 4-14 mL/kg/h based on response 1
• Urine sodium <30 mmol/L predicts good response to saline (71-100% positive predictive value) 1

Euvolemic Hyponatremia (SIADH):

• Fluid restriction to 1 L/day is the cornerstone of treatment 1, 4, 6
• If no response to fluid restriction, add oral sodium chloride 100 mEq three times daily 1, 7
• For resistant cases, consider vasopressin receptor antagonists (tolvaptan 15 mg once daily, titrate to 30-60 mg) 1, 3
• Alternative options: urea, demeclocycline, or lithium 1, 4

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis):

• Fluid restriction to 1-1.5 L/day for sodium <125 mmol/L 1, 6
• Discontinue diuretics temporarily if sodium <125 mmol/L 1
• For cirrhotic patients, consider albumin infusion alongside fluid restriction 1
• Avoid hypertonic saline unless life-threatening symptoms present, as it worsens edema and ascites 1
• Vaptans may be considered for persistent severe hyponatremia despite fluid restriction, but use with extreme caution in cirrhosis due to higher risk of GI bleeding (10% vs 2% placebo) 1, 3

Special Considerations for Neurosurgical Patients

Distinguish between SIADH and Cerebral Salt Wasting (CSW)—they require opposite treatments 1:

SIADH characteristics:

• Euvolemic state
• Urine sodium >20-40 mmol/L
• Urine osmolality >300 mOsm/kg
• Treatment: fluid restriction 1

CSW characteristics:

• True hypovolemia with low CVP (<6 cm H₂O)
• Urine sodium >20 mmol/L despite volume depletion
• Clinical signs of volume depletion 1
• Treatment: volume and sodium replacement with isotonic or hypertonic saline, NOT fluid restriction 1
• For severe symptoms: 3% hypertonic saline plus fludrocortisone 0.1-0.2 mg daily 1

In subarachnoid hemorrhage patients at risk of vasospasm, NEVER use fluid restriction—it worsens outcomes 1.

Monitoring During Treatment

Frequency of sodium monitoring 1:

• Severe symptoms: every 2 hours during initial correction
• After symptom resolution: every 4 hours
• Mild symptoms or asymptomatic: every 4-6 hours initially, then daily

Calculate sodium deficit using formula: Desired increase in Na (mEq/L) × (0.5 × ideal body weight in kg) 1, 7.

Management of Overcorrection

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

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

Common Pitfalls to Avoid

Critical errors that worsen outcomes 1:

• Overly rapid correction exceeding 8 mmol/L in 24 hours—causes osmotic demyelination syndrome
• Using fluid restriction in cerebral salt wasting—worsens outcomes
• Inadequate monitoring during active correction
• Failing to recognize and treat the underlying cause
• Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms
• Ignoring mild hyponatremia (130-135 mmol/L) as clinically insignificant—it increases fall risk (21% vs 5%) and mortality (60-fold increase with sodium <130 mmol/L) 1, 2, 4

Clinical Significance

Even mild chronic hyponatremia is associated with significant morbidity 2, 4:

• Cognitive impairment and attention deficits
• Increased fall risk and fractures
• Increased hospital mortality
• In cirrhotic patients: increased risk of spontaneous bacterial peritonitis (OR 3.40), hepatorenal syndrome (OR 3.45), and hepatic encephalopathy (OR 2.36) 1

Correction of hyponatremia significantly improves cognitive function, quality of life, and reduces fall risk 2.