Management of Hyponatremia
Initial Assessment and Classification
Hyponatremia management depends critically on three factors: symptom severity (asymptomatic, mild, or severe), duration (acute <48 hours vs. chronic >48 hours), and volume status (hypovolemic, euvolemic, or hypervolemic). 1
Assess volume status through physical examination looking for:
- 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
Obtain essential laboratory tests including serum and urine osmolality, urine sodium concentration, serum creatinine, and thyroid function to determine the underlying cause 1
Treatment Based on Symptom Severity
Severe Symptomatic Hyponatremia (Seizures, Coma, Altered Mental Status)
This is a medical emergency requiring immediate hypertonic saline regardless of volume status. 1
- Administer 3% hypertonic saline as 100 mL boluses over 10 minutes, repeatable up to three times at 10-minute intervals 1
- Target correction of 6 mmol/L over the first 6 hours or until severe symptoms resolve 1
- Never exceed 8 mmol/L correction in any 24-hour period to prevent osmotic demyelination syndrome 1
- Check serum sodium every 2 hours during initial correction 1
- For high-risk patients (cirrhosis, alcoholism, malnutrition), limit correction to 4-6 mmol/L per day with an absolute maximum of 8 mmol/L in 24 hours 1
Mild to Moderate Symptomatic Hyponatremia
Treatment depends on volume status and underlying cause 1
Treatment Based on Volume Status
Hypovolemic Hyponatremia
Discontinue diuretics immediately and administer isotonic saline (0.9% NaCl) for volume repletion. 1
- Initial infusion 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 (positive predictive value 71-100%) 1
- In cirrhotic patients, consider albumin infusion (8 g per liter of ascites removed) alongside isotonic saline 2, 1
- Correction rate should not exceed 8 mmol/L in 24 hours 1
Euvolemic Hyponatremia (SIADH)
Fluid restriction to 1 L/day is the cornerstone of treatment. 1
- If fluid restriction fails after 24-48 hours, add oral sodium chloride 100 mEq three times daily 1
- For resistant cases, consider vasopressin receptor antagonists (tolvaptan 15 mg once daily, titrate to 30-60 mg) 1
- Alternative pharmacological options include urea, demeclocycline, or loop diuretics 1
- Never exceed 8 mmol/L correction in 24 hours 1
Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)
Implement fluid restriction to 1-1.5 L/day for serum sodium <125 mmol/L. 2, 1
- Temporarily discontinue diuretics if sodium <125 mmol/L 2, 1
- In cirrhotic patients, consider albumin infusion alongside fluid restriction 2, 1
- Avoid hypertonic saline unless life-threatening symptoms are present, as it may worsen ascites and edema 1
- For heart failure patients, optimize guideline-directed medical therapy (ACE inhibitors, beta-blockers) before adding additional interventions 1
- Vasopressin receptor antagonists may be considered for persistent severe hyponatremia despite fluid restriction 1
Special Populations and Considerations
Cirrhotic Patients
Cirrhotic patients require exceptionally cautious correction (4-6 mmol/L per day maximum) due to heightened risk of osmotic demyelination syndrome. 1
- Hyponatremia in cirrhosis increases risk of spontaneous bacterial peritonitis (OR 3.40), hepatorenal syndrome (OR 3.45), and hepatic encephalopathy (OR 2.36) 1
- Sodium restriction (not fluid restriction) results in weight loss, as fluid passively follows sodium 2, 1
- Tolvaptan should be used with extreme caution due to higher risk of gastrointestinal bleeding (10% vs. 2% placebo) 1
Neurosurgical Patients
Distinguish between SIADH and cerebral salt wasting (CSW), as they require opposite treatments. 1
- SIADH: euvolemic, treat with fluid restriction 1
- CSW: hypovolemic with CVP <6 cm H₂O, treat with volume and sodium replacement (isotonic or hypertonic saline), never fluid restriction 1
- In subarachnoid hemorrhage patients at risk of vasospasm, fluid restriction is contraindicated 1
- Consider fludrocortisone 0.1-0.2 mg daily for CSW or to prevent vasospasm 1
Patients with Advanced Liver Disease, Alcoholism, or Malnutrition
These high-risk patients have a 0.5-1.5% risk of osmotic demyelination syndrome even with careful correction. 1
- Limit correction to 4-6 mmol/L per day, absolute maximum 8 mmol/L in 24 hours 1
- Monitor for signs of osmotic demyelination syndrome (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically 2-7 days after rapid correction 1
Management of Overcorrection
If sodium correction exceeds 8 mmol/L in 24 hours, immediately discontinue current fluids and switch to D5W (5% dextrose in water). 1
- Consider administering desmopressin to slow or reverse the rapid rise 1
- Target is to bring total 24-hour correction back to ≤8 mmol/L from baseline 1
Monitoring Requirements
- Severe symptoms: Check serum sodium every 2 hours during initial correction 1
- After symptom resolution: Check every 4-6 hours 1
- Mild symptoms or asymptomatic: Check every 24-48 hours initially 1
- Monitor for signs of volume overload or depletion during treatment 1
Common Pitfalls to Avoid
- Never correct chronic hyponatremia faster than 8 mmol/L in 24 hours—this causes osmotic demyelination syndrome 1
- Never use fluid restriction in cerebral salt wasting—this worsens outcomes and can be fatal 1
- Never ignore 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, 3
- Never use hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms—it worsens fluid overload 1
- Inadequate monitoring during active correction can lead to overcorrection 1
- Failing to recognize and treat the underlying cause leads to recurrence 1