Management of Hyponatremia by Severity Grade
Classification and Severity Grading
Hyponatremia is classified by serum sodium concentration: mild (130-134 mEq/L), moderate (120-125 mEq/L), and severe (<120 mEq/L), with management determined by both the sodium level and symptom severity rather than the number alone. 1, 2, 3
- Symptom severity depends on rapidity of onset, duration, and degree of sodium reduction 4, 3
- Acute hyponatremia (<48 hours) carries higher risk of cerebral edema and severe neurological symptoms 1
- Chronic hyponatremia (>48 hours) is associated with cognitive impairment, gait disturbances, falls (23.8% vs 16.4% in normonatremic patients), and fractures 4
Initial Assessment Framework
Volume Status Determination
The first critical step is categorizing patients as hypovolemic, euvolemic, or hypervolemic, as this fundamentally determines treatment approach. 1, 3, 5
- Hypovolemic signs: orthostatic hypotension, dry mucous membranes, decreased skin turgor, flat neck veins 1
- Euvolemic signs: normal volume status without edema or dehydration 1
- Hypervolemic signs: peripheral edema, ascites, jugular venous distention 1, 5
Essential Laboratory Workup
- Serum and urine osmolality, urine sodium, uric acid 1
- Urine sodium <30 mmol/L predicts saline responsiveness (71-100% positive predictive value) 1
- Serum uric acid <4 mg/dL suggests SIADH (73-100% positive predictive value) 1
Management by Severity and Symptom Status
Severe Symptomatic Hyponatremia (Medical Emergency)
For patients with severe symptoms (seizures, coma, altered mental status, cardiorespiratory distress), immediately administer 3% hypertonic saline with a target correction of 6 mmol/L over 6 hours or until symptoms resolve. 1, 4, 3
- Administer 100 mL boluses of 3% saline over 10 minutes, repeatable up to three times at 10-minute intervals 1
- Critical safety limit: Never exceed 8 mmol/L total correction in 24 hours to prevent osmotic demyelination syndrome 1, 4, 3
- Monitor serum sodium every 2 hours during initial correction 1
- Consider ICU admission for continuous monitoring 1
Moderate Hyponatremia (120-125 mEq/L) with Mild Symptoms
For patients with moderate hyponatremia and mild symptoms (nausea, headache, weakness, muscle cramps), treatment is based on volume status with slower correction rates. 2, 3
Hypovolemic:
- Discontinue diuretics immediately 1
- Administer isotonic saline (0.9% NaCl) for volume repletion at 15-20 mL/kg/h initially, then 4-14 mL/kg/h 1
- Target correction: 4-8 mmol/L per day, maximum 8 mmol/L in 24 hours 1
Euvolemic (SIADH):
- Fluid restriction to 1 L/day as first-line treatment 1, 3
- If no response, add oral sodium chloride 100 mEq three times daily 1
- Consider vaptans (tolvaptan 15 mg daily, titrate to 30-60 mg) for resistant cases 1, 6
Hypervolemic (heart failure, cirrhosis):
- Fluid restriction to 1-1.5 L/day 1, 2, 3
- Discontinue diuretics temporarily if sodium <125 mmol/L 1
- For cirrhosis: consider albumin infusion alongside fluid restriction 1
- Avoid hypertonic saline unless life-threatening symptoms present 1
Mild Hyponatremia (130-134 mEq/L)
Even mild hyponatremia requires attention due to increased fall risk and mortality, though treatment is generally conservative. 1, 4
- Continue diuretic therapy with close electrolyte monitoring if sodium >126 mmol/L 1
- Implement fluid restriction to 1-1.5 L/day for hypervolemic patients 2
- Address underlying causes (medications, SIADH, heart failure) 3, 5
- Monitor sodium levels every 24-48 hours initially 1
Critical Correction Rate Guidelines
Standard Patients
High-Risk Patients (Cirrhosis, Alcoholism, Malnutrition)
- More cautious correction: 4-6 mmol/L per day, maximum 8 mmol/L in 24 hours 1, 2
- These patients have significantly higher risk of osmotic demyelination syndrome 1
Management of Overcorrection
- If correction exceeds 8 mmol/L in 24 hours, immediately discontinue current fluids 1
- Switch to D5W (5% dextrose in water) to relower sodium 1
- Consider desmopressin to slow or reverse rapid rise 1
Special Considerations by Etiology
Neurosurgical Patients: SIADH vs Cerebral Salt Wasting
Distinguishing between SIADH and cerebral salt wasting (CSW) is critical as they require opposite treatments. 1
- SIADH: Euvolemic, treat with fluid restriction 1
- CSW: Hypovolemic with high urine sodium despite volume depletion, treat with volume and sodium replacement, NOT fluid restriction 1
- For subarachnoid hemorrhage at risk of vasospasm: never use fluid restriction 1
- Consider fludrocortisone 0.1-0.2 mg daily for CSW 1
Cirrhotic Patients
- Hyponatremia increases risk of spontaneous bacterial peritonitis (OR 3.40), hepatorenal syndrome (OR 3.45), and hepatic encephalopathy (OR 2.36) 1
- Tolvaptan carries higher risk of gastrointestinal bleeding in cirrhosis (10% vs 2% placebo) 1, 6
- Sodium restriction (not fluid restriction) results in weight loss as fluid follows sodium 1
Common Pitfalls to Avoid
- Never correct chronic hyponatremia faster than 8 mmol/L in 24 hours—this causes osmotic demyelination syndrome 1, 4, 7
- Never use fluid restriction in cerebral salt wasting—this worsens outcomes 1
- Never use hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms 1
- Inadequate monitoring during active correction leads to overcorrection 1
- Failing to identify and treat underlying cause leads to recurrence 1, 2
- Using fluid restriction in subarachnoid hemorrhage patients at risk of vasospasm 1
Pharmacological Options
Vaptans (Vasopressin Receptor Antagonists)
- Tolvaptan 15 mg once daily, titrate to 30-60 mg for euvolemic or hypervolemic hyponatremia resistant to fluid restriction 1, 6
- Increases serum sodium significantly more than placebo 1, 6
- Contraindicated with strong CYP3A inhibitors 6
- Monitor closely to avoid overly rapid correction 1, 6
- Common side effects: thirst, dry mouth, polyuria 6