At what level of hyponatremia (low sodium levels) should correction be started in patients?

When to Start Correction of Hyponatremia

Hyponatremia correction should be initiated when serum sodium falls below 135 mEq/L, with the urgency and aggressiveness of treatment determined by symptom severity rather than the absolute sodium level alone. 1

Threshold for Investigation and Treatment

• Serum sodium <135 mEq/L defines hyponatremia and warrants initial assessment, including serum and urine osmolality, urine electrolytes, and volume status evaluation 1
• Full diagnostic workup and active treatment consideration begins at sodium <131 mEq/L, though even mild hyponatremia (130-135 mEq/L) should not be dismissed as clinically insignificant 1
• Even mild chronic hyponatremia (130-135 mEq/L) carries significant risks, including a 60-fold increased mortality (11.2% vs 0.19%), increased fall risk (21% vs 5%), cognitive impairment, and gait disturbances 1, 2, 3

Treatment Urgency Based on Symptom Severity

Severe Symptomatic Hyponatremia (Medical Emergency)

• Immediate treatment with 3% hypertonic saline is required for patients with severe symptoms (seizures, coma, altered consciousness, confusion, respiratory distress) regardless of the absolute sodium level 1, 4
• Target correction of 6 mEq/L over 6 hours or until severe symptoms resolve, with total correction not exceeding 8 mEq/L in 24 hours 1, 5
• Monitor serum sodium every 2 hours during initial correction 1

Moderate Symptomatic Hyponatremia

• Patients with moderate symptoms (nausea, vomiting, headache, weakness, mild confusion) at sodium 120-125 mEq/L require active treatment 1, 2
• Fluid restriction to 1-1.5 L/day is first-line for euvolemic/hypervolemic patients, with consideration of oral sodium supplementation (100 mEq three times daily) if fluid restriction fails 1, 6

Asymptomatic or Mildly Symptomatic Hyponatremia

• Sodium 126-135 mEq/L in asymptomatic patients can often be managed conservatively with close monitoring and treatment of underlying cause 1
• However, treatment should still be considered even at these levels given the association with falls, fractures, cognitive impairment, and increased mortality 2, 3

Volume Status-Based Treatment Thresholds

Hypovolemic Hyponatremia

• Begin isotonic saline (0.9% NaCl) for volume repletion immediately when hypovolemia is confirmed (orthostatic hypotension, dry mucous membranes, urine sodium <30 mEq/L) 1
• Discontinue diuretics immediately if sodium <125 mEq/L 1

Euvolemic Hyponatremia (SIADH)

• Fluid restriction to 1 L/day is first-line treatment for sodium <135 mEq/L 1
• Add oral sodium chloride 100 mEq three times daily if no response to fluid restriction 1, 6
• Consider vaptans (tolvaptan 15 mg daily) for persistent hyponatremia despite fluid restriction, particularly if sodium <125 mEq/L 1, 7

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

• Implement fluid restriction to 1-1.5 L/day when sodium drops below 125 mEq/L 1
• For cirrhotic patients, consider albumin infusion alongside fluid restriction 1
• Avoid hypertonic saline unless life-threatening symptoms are present, as it worsens fluid overload 1

Critical Safety Considerations

• Never exceed correction of 8 mEq/L in 24 hours for chronic hyponatremia (>48 hours duration) to prevent osmotic demyelination syndrome 1, 7, 3
• High-risk patients (advanced liver disease, alcoholism, malnutrition, prior encephalopathy) require even slower correction at 4-6 mEq/L per day 1
• Acute hyponatremia (<48 hours) can be corrected more rapidly without risk of osmotic demyelination, but still avoid exceeding 10-12 mEq/L in 24 hours 1, 5

Special Population Considerations

Neurosurgical Patients

• Distinguish between SIADH and cerebral salt wasting (CSW), as they require opposite treatments 1
• CSW requires volume and sodium replacement, not fluid restriction 1
• Never use fluid restriction in subarachnoid hemorrhage patients at risk of vasospasm 1

Cirrhotic Patients

• Sodium ≤130 mEq/L increases risk of spontaneous bacterial peritonitis (OR 3.40), hepatorenal syndrome (OR 3.45), and hepatic encephalopathy (OR 2.36) 1
• Only 1.2% of cirrhotic patients with ascites have sodium ≤120 mEq/L, highlighting the severity when it occurs 1

Common Pitfalls to Avoid

• Do not ignore mild hyponatremia (130-135 mEq/L) as clinically insignificant—it carries real morbidity and mortality risk 1, 2
• Do not delay treatment while pursuing extensive diagnostic workup in symptomatic patients—treat based on symptom severity first 4
• Do not use fluid restriction in cerebral salt wasting—this worsens outcomes 1
• Do not correct chronic hyponatremia too rapidly—overly rapid correction (>8 mEq/L in 24 hours) causes osmotic demyelination syndrome 1, 7, 8