Hyponatremia Correction

Step 1 - Classify Before Treating

1. Acuity - Acute (< 48 h) vs. chronic (> 48 h, or unknown duration which is treated as chronic)
2. Severity of symptoms - Mild (headache, nausea) vs. severe (seizures, obtundation, coma)
3. Volume status - Hypovolemic / Euvolemic / Hypervolemic

Common Causes by Volume Status

Step 2 - Determine the Correction Strategy

A. Acute Symptomatic Hyponatremia (< 48 h, or seizures/coma regardless of chronicity)

• Severe symptoms (seizures, coma): 100 mL of 3% NaCl IV over 10 minutes, repeated up to 2 more times (total up to 300 mL)
• Mild to moderate symptoms: 3% NaCl infusion at 0.5-2 mL/kg/hour
• Rate of correction is not restricted in true acute hyponatremia
• Add supplemental O2 and ventilatory support if pulmonary edema develops; IV loop diuretics treat pulmonary edema and increase free water excretion

"A bolus of 100 mL of hypertonic saline is more effective than an infusion, rapidly improving both serum sodium and mental status." - Harrison's Principles of Internal Medicine 22E

B. Chronic Hyponatremia (> 48 h, or unknown duration)

Correction Rate Limits

• Serum Na < 105 mmol/L
• Hypokalemia
• Alcohol use disorder / malnutrition
• Advanced liver disease (cirrhosis)
• Beer potomania

"The rate of correction should not exceed 8 mmol/L in any 24-hour period in patients at high risk of ODS, and not exceed 10-12 mmol/L in any 24-hour period for patients at normal risk." - Goldman-Cecil Medicine

Step 3 - Treatment by Cause

Hypovolemic Hyponatremia

• IV isotonic (normal) saline to restore volume
• ADH will normalize once volume is restored, which can sometimes cause a rapid spontaneous rise in sodium - monitor closely

Euvolemic Hyponatremia (SIADH)

• Fluid restriction (typically ≥ 500 mL less than urine output per day)
• Use the urine-to-plasma electrolyte ratio ([uNa + uK] / pNa) to guide restriction aggressiveness:
  • Ratio > 1 → aggressive restriction < 500 mL/day
  • Ratio ~1 → restrict to 500-700 mL/day
  • Ratio < 1 → restrict to < 1 L/day
• Oral solute loading: salt tablets + furosemide (20 mg BID) to increase free water excretion
• Oral urea is also effective and well-tolerated
• Vaptans (V2-receptor antagonists): tolvaptan 15-60 mg/day orally; conivaptan IV - indicated for persistent SIADH unresponsive to fluid restriction; NOT for hypovolemic or acute hyponatremia; tolvaptan is restricted to < 1-2 months due to hepatotoxicity risk, and is contraindicated in cirrhosis
• Demeclocycline - inhibits ADH at collecting duct; rarely used now due to nephrotoxicity

Hypervolemic Hyponatremia (heart failure, cirrhosis, CKD)

• Sodium + water restriction
• Loop diuretics
• Treat underlying condition (e.g., optimize ACE inhibition in heart failure)
• Tolvaptan may be used in heart failure but NOT in cirrhosis

Step 4 - Sodium Deficit Formula

Step 5 - Managing Overcorrection

• If starting Na was ≥ 120 mmol/L → re-lowering is often unnecessary
• If starting Na was < 120 mmol/L → re-lower to target:
  1. DDAVP 2-4 mcg IV/SC every 8 hours (clamps further water excretion)
  2. D5W IV at ~3 mL/kg/hour to replace free water
  3. Withhold next vaptan dose if correction > 8 mmol/L
  4. Consider dexamethasone 4 mg IV every 6 hours for 24-48 h if overcorrection has occurred
  5. Check Na hourly until target is reached

ODS (Osmotic Demyelination Syndrome) - Key Points

• Occurs days after rapid correction of chronic hyponatremia
• Affects the pons most often (central pontine myelinolysis); can also affect extrapontine sites
• Clinical features: fluctuating consciousness, pseudobulbar palsy, quadriparesis, ataxia, dysarthria, dysphagia
• Diagnosis: MRI of brainstem
• Prevention is the only reliable strategy - there is no established treatment once it develops

Practical Summary