How should I evaluate and manage moderate-to-severe hyponatremia with a serum sodium of 123 mmol/L?

Evaluation and Management of Moderate Hyponatremia (Serum Sodium 123 mmol/L)

Immediate Assessment and Diagnostic Workup

For a serum sodium of 123 mmol/L, you must immediately assess symptom severity and volume status, then initiate appropriate treatment while simultaneously pursuing diagnostic workup—do not delay treatment while establishing the underlying cause. 1

Essential Initial Laboratory Tests

• Serum osmolality to confirm hypotonic hyponatremia and exclude pseudohyponatremia 1
• Urine osmolality and urine sodium concentration to differentiate between causes 1
• Serum creatinine, BUN, glucose, and uric acid (uric acid <4 mg/dL has 73-100% positive predictive value for SIADH) 1
• Thyroid-stimulating hormone (TSH) and cortisol to exclude hypothyroidism and adrenal insufficiency 1
• Complete blood count, liver function tests to assess for underlying conditions 1

Volume Status Assessment

Physical examination alone has poor accuracy (sensitivity 41%, specificity 80%), so combine clinical findings with laboratory data 1:

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

---

Treatment Based on Symptom Severity

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

Administer 3% hypertonic saline immediately with a target correction of 6 mmol/L over 6 hours or until severe symptoms resolve. 1

• Dosing: Give 100 mL boluses of 3% NaCl over 10 minutes, repeating up to three times at 10-minute intervals 1, 2
• Monitoring: Check serum sodium every 2 hours during initial correction 1
• Critical safety limit: Total correction must not exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome 1
• ICU admission is required for close monitoring 1

Mild to Moderate Symptoms (Nausea, Headache, Confusion)

Treatment depends on volume status (see below), but correction should be more gradual than in severe cases 1. Monitor serum sodium every 4-6 hours initially 1.

---

Treatment Based on Volume Status

Hypovolemic Hyponatremia (True Volume Depletion)

Administer isotonic saline (0.9% NaCl) for volume repletion. 1

• Initial infusion rate: 15-20 mL/kg/h for the first hour, then 4-14 mL/kg/h based on response 1
• Diagnostic clue: Urine sodium <30 mmol/L has 71-100% positive predictive value for saline responsiveness 1
• Discontinue diuretics immediately if they are contributing 1
• Correction rate: 4-8 mmol/L per day, maximum 8 mmol/L in 24 hours 1

Euvolemic Hyponatremia (SIADH)

Fluid restriction to 1 L/day is the cornerstone of treatment. 1

• First-line: Restrict fluids to <1 L/day 1
• If no response: Add oral sodium chloride 100 mEq three times daily 1
• Pharmacologic options for resistant cases: Vasopressin receptor antagonists (tolvaptan 15 mg once daily, titrate to 30-60 mg), urea, demeclocycline, or loop diuretics 1, 3
• For severe symptoms: 3% hypertonic saline with target correction of 6 mmol/L over 6 hours 1

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

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

• Discontinue or reduce diuretics temporarily if sodium <125 mmol/L 1
• For cirrhotic patients: Consider albumin infusion (8 g per liter of ascites removed) alongside fluid restriction 1
• Avoid hypertonic saline unless life-threatening symptoms are present, as it may worsen edema and ascites 1
• Vasopressin receptor antagonists (tolvaptan) may be considered for persistent severe hyponatremia despite fluid restriction, but use with extreme caution in cirrhosis due to hepatotoxicity risk (4.4% developed ALT >3× ULN) and increased GI bleeding risk (10% vs 2% placebo) 1, 3

---

Critical Correction Rate Guidelines

The single most important safety principle: Never exceed 8 mmol/L correction in any 24-hour period. 1

Standard-Risk Patients

• Target: 4-8 mmol/L per day 1
• Absolute maximum: 10-12 mmol/L in 24 hours 1

High-Risk Patients (Advanced Liver Disease, Alcoholism, Malnutrition, Prior Encephalopathy)

• Target: 4-6 mmol/L per day 1
• Absolute maximum: 8 mmol/L in 24 hours 1
• Risk of osmotic demyelination syndrome: 0.5-1.5% even with careful correction 1

---

Management of Overcorrection

If sodium rises excessively (>8 mmol/L in 24 hours), immediately intervene to prevent osmotic demyelination syndrome. 1

• Stop current fluids and switch to D5W (5% dextrose in water) 1
• Administer desmopressin to slow or reverse the rapid rise 1
• Target: Bring total 24-hour correction back to ≤8 mmol/L from baseline 1
• Watch for osmotic demyelination syndrome signs (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically 2-7 days after rapid correction 1

---

Special Considerations

Neurosurgical Patients (Cerebral Salt Wasting vs SIADH)

Distinguishing cerebral salt wasting (CSW) from SIADH is critical because they require opposite treatments. 1

• CSW characteristics: True hypovolemia, CVP <6 cm H₂O, urine sodium >20 mmol/L despite volume depletion 1
• CSW treatment: Volume and sodium replacement with isotonic or hypertonic saline, fludrocortisone 0.1-0.2 mg daily for severe cases 1
• Never use fluid restriction in CSW—it worsens outcomes and can precipitate cerebral ischemia 1
• In subarachnoid hemorrhage patients at risk of vasospasm: Avoid fluid restriction; consider fludrocortisone or hydrocortisone 1

Cirrhotic Patients

• Hyponatremia in cirrhosis increases risk of spontaneous bacterial peritonitis (OR 3.40), hepatorenal syndrome (OR 3.45), and hepatic encephalopathy (OR 2.36) 1
• Correction rates must be especially cautious (4-6 mmol/L per day maximum) 1
• Tolvaptan use carries higher risks in cirrhosis: hepatotoxicity and GI bleeding 1, 3

---

Common Pitfalls to Avoid

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