How should hyponatremia be corrected, taking into account acute versus chronic onset, symptom severity, volume status, and safe limits for serum sodium increase?

Hyponatremia Correction

Hyponatremia correction must be guided by symptom severity and chronicity, with the absolute priority being prevention of osmotic demyelination syndrome by never exceeding 8 mmol/L correction in any 24-hour period, while simultaneously treating severe symptoms aggressively enough to prevent herniation and death. 1

Immediate Assessment: Symptom Severity Determines Urgency

The first decision point is whether the patient has severe symptoms (seizures, coma, altered consciousness, respiratory distress) versus mild symptoms (nausea, headache, confusion) versus asymptomatic hyponatremia. 1, 2

Severe Symptomatic Hyponatremia (Medical Emergency)

Administer 3% hypertonic saline immediately with a target of raising sodium by 6 mmol/L over 6 hours or until severe symptoms resolve—this is sufficient to reverse impending herniation. 1, 3

• Give 100 mL boluses of 3% NaCl over 10 minutes, repeating up to three times at 10-minute intervals if needed. 1
• Check serum sodium every 2 hours during this acute phase. 1
• Stop hypertonic saline once severe symptoms resolve, then transition to protocols for mild/asymptomatic hyponatremia. 4
• The total 24-hour correction must not exceed 8 mmol/L to prevent osmotic demyelination syndrome. 1, 3

Critical pitfall: If you correct 6 mmol/L in the first 6 hours, you can only allow an additional 2 mmol/L rise over the remaining 18 hours. 1, 4

Mild Symptomatic or Asymptomatic Hyponatremia

The approach depends on volume status and chronicity (acute <48 hours versus chronic >48 hours). 1, 5

Volume Status Classification: The Key Diagnostic Step

Assess for hypovolemic, euvolemic, or hypervolemic hyponatremia through physical examination (orthostatic hypotension, skin turgor, edema, ascites, jugular venous distension) and laboratory studies (urine sodium, urine osmolality). 1, 5

Hypovolemic Hyponatremia

Administer isotonic saline (0.9% NaCl) for volume repletion at 15-20 mL/kg/h initially, 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
• Discontinue diuretics if sodium <125 mmol/L. 1
• For cirrhotic patients, consider albumin infusion (8 g per liter of ascites removed) alongside isotonic saline. 1
• Correction rate: 4-6 mmol/L per day maximum in cirrhotic or malnourished patients; standard patients 4-8 mmol/L per day. 1

Euvolemic Hyponatremia (SIADH)

Fluid restriction to 1 L/day is the cornerstone of treatment. 1, 5

• If no response to fluid restriction, 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). 6, 7
• Urea is an alternative option with fewer side effects than vaptans. 7, 8
• Avoid fluid restriction in neurosurgical patients with cerebral salt wasting—this requires volume and sodium replacement, not restriction. 1

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

Fluid restriction to 1-1.5 L/day for sodium <125 mmol/L. 1, 5

• Discontinue diuretics temporarily if sodium <125 mmol/L. 1
• For cirrhotic patients, albumin infusion may be beneficial. 1
• Avoid hypertonic saline unless life-threatening symptoms are 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 hepatotoxicity risk (4.4% ALT >3× ULN) and increased GI bleeding (10% vs 2% placebo). 1, 6

Safe Correction Limits: The Non-Negotiable Rules

Standard-risk patients: Maximum 8 mmol/L in 24 hours, target 4-8 mmol/L per day. 1, 3

High-risk patients (advanced liver disease, alcoholism, malnutrition, prior encephalopathy, severe hyponatremia <120 mmol/L): Maximum 8 mmol/L in 24 hours, target 4-6 mmol/L per day. 1, 3

Monitoring Frequency

• Severe symptoms: Every 2 hours during initial correction, then every 4 hours after symptom resolution. 1
• Mild symptoms or asymptomatic: Every 4-6 hours initially, then daily. 1

Acute Versus Chronic Hyponatremia: Different Risks

Acute hyponatremia (<48 hours) causes severe brain swelling and can be corrected more rapidly (up to 1 mmol/L per hour) without risk of osmotic demyelination. 1, 3, 9

Chronic hyponatremia (>48 hours) has minimal brain swelling but carries high risk of osmotic demyelination if corrected too rapidly—the 8 mmol/L/24-hour limit is absolute. 1, 3

Critical distinction: In practice, assume hyponatremia is chronic unless you have clear documentation of acute onset, because the consequences of overcorrecting chronic hyponatremia (osmotic demyelination) are devastating and irreversible. 1, 3

Management of Overcorrection

If sodium rises >8 mmol/L in 24 hours, immediately:

• Stop all hypertonic fluids and switch to D5W (5% dextrose in water). 1
• Administer desmopressin to slow or reverse the rapid rise. 1
• Target is to bring the total 24-hour correction back to ≤8 mmol/L from baseline. 1

Special Populations

Neurosurgical Patients (Subarachnoid Hemorrhage, Brain Injury)

Distinguish SIADH from cerebral salt wasting (CSW)—they require opposite treatments. 1

• CSW: True hypovolemia with urine sodium >20 mmol/L despite volume depletion → treat with volume and sodium replacement, consider fludrocortisone 0.1-0.2 mg daily. 1
• SIADH: Euvolemia with urine sodium >20-40 mmol/L → treat with fluid restriction. 1
• Never use fluid restriction in subarachnoid hemorrhage patients at risk of vasospasm. 1

Cirrhotic Patients

• Hyponatremia in cirrhosis is usually hypervolemic and dilutional. 1
• Correction rates must be especially cautious (4-6 mmol/L per day maximum) due to exceptionally high risk of osmotic demyelination. 1
• Sodium restriction (not fluid restriction) results in weight loss, as fluid follows sodium. 1
• Hyponatremia <130 mmol/L increases risk of spontaneous bacterial peritonitis (OR 3.40), hepatorenal syndrome (OR 3.45), and hepatic encephalopathy (OR 2.36). 1

Common Pitfalls

• Ignoring mild hyponatremia (130-135 mmol/L) as clinically insignificant—even mild chronic hyponatremia increases mortality 60-fold and causes cognitive impairment, falls, and fractures. 1, 2, 7
• Using fluid restriction in cerebral salt wasting—this worsens outcomes and can be fatal. 1
• Correcting chronic hyponatremia faster than 8 mmol/L in 24 hours—this causes osmotic demyelination syndrome (dysarthria, dysphagia, quadriparesis) appearing 2-7 days after overcorrection. 1, 3
• Inadequate monitoring during active correction—sodium can rise unpredictably, especially after volume repletion in hypovolemic patients. 1
• Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms—this worsens fluid overload. 1