Correction of Chronic Hyponatremia
For chronic hyponatremia (>48 hours duration), the correction rate must not exceed 8 mmol/L in 24 hours, with high-risk patients requiring even slower correction at 4-6 mmol/L per day to prevent osmotic demyelination syndrome. 1
Initial Assessment and Classification
Before initiating treatment, determine three critical factors 1:
- Volume status: Assess for hypovolemia (orthostatic hypotension, dry mucous membranes, decreased skin turgor), euvolemia (no edema, normal blood pressure), or hypervolemia (peripheral edema, ascites, jugular venous distention) 1
- Symptom severity: Mild symptoms include nausea, forgetfulness, apathy; severe symptoms include confusion, seizures, or coma 2, 3
- Serum sodium level: Mild (130-135 mmol/L), moderate (120-129 mmol/L), or severe (<120 mmol/L) 1, 2
Obtain serum and urine osmolality, urine sodium concentration, and urine electrolytes to determine the underlying etiology 1. A urine sodium >20-40 mmol/L with urine osmolality >300 mOsm/kg suggests SIADH in euvolemic patients 1, 3.
Treatment Based on Volume Status
Hypovolemic Hyponatremia
Discontinue diuretics immediately and administer isotonic saline (0.9% NaCl) for volume repletion 1. A urine sodium <30 mmol/L predicts 71-100% response to saline infusion 1. Once euvolemia is achieved, reassess sodium levels and adjust therapy accordingly 1.
Euvolemic Hyponatremia (SIADH)
Fluid restriction to 1 L/day is the cornerstone of treatment for SIADH 1, 2, 4. If no response to fluid restriction after 24-48 hours, add oral sodium chloride 100 mEq three times daily 1. For resistant cases, consider 1, 2:
- Urea (15-30 g/day in divided doses) - effective but has poor palatability 5
- Demeclocycline (600-1200 mg/day) - reserved for persistent cases 2, 4
- Loop diuretics - useful for chronic SIADH management 4, 6
Vaptans (tolvaptan) may be considered for clinically significant hyponatremia resistant to fluid restriction, starting at 15 mg once daily 1, 7. However, tolvaptan must be initiated in a hospital setting with close sodium monitoring, as it can cause overly rapid correction 7. The dose can be titrated to 30 mg, then 60 mg once daily after at least 24 hours 7. Do not use tolvaptan for more than 30 days due to hepatotoxicity risk 7.
Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)
Implement fluid restriction to 1-1.5 L/day for serum sodium <125 mmol/L 1, 6. Temporarily discontinue diuretics if sodium drops below 125 mmol/L 1. For cirrhotic patients, consider albumin infusion alongside fluid restriction 1, 5.
Avoid hypertonic saline in hypervolemic hyponatremia unless life-threatening symptoms are present, as it worsens edema and ascites 1. Vaptans may be considered for persistent severe hyponatremia despite fluid restriction and maximization of guideline-directed medical therapy 1, 7, but use with extreme caution in cirrhosis due to higher risk of gastrointestinal bleeding (10% vs 2% placebo) 1.
Critical Correction Rate Guidelines
Standard correction rate: 4-8 mmol/L per day, not exceeding 8 mmol/L in 24 hours 1, 3, 6. This limit applies regardless of treatment modality used 1.
High-risk patients require slower correction at 4-6 mmol/L per day 1, 7, 5. High-risk populations include 1, 7:
- Advanced liver disease or cirrhosis
- Chronic alcoholism
- Severe malnutrition
- Prior encephalopathy
- Serum sodium <120 mmol/L
Monitor serum sodium every 4 hours initially during active correction, then daily once stable 1. If overcorrection occurs (>8 mmol/L in 24 hours), immediately discontinue current fluids, switch to D5W (5% dextrose in water), and consider desmopressin to relower sodium levels 1.
Severely Symptomatic Chronic Hyponatremia
For patients with severe neurological symptoms (seizures, coma, altered mental status), administer 3% hypertonic saline with initial goal to correct 6 mmol/L over 6 hours or until symptoms resolve 1, 3, 6. This can be given as 100 mL boluses over 10 minutes, repeated up to three times at 10-minute intervals 1. Total correction must still not exceed 8 mmol/L in 24 hours 1, 7.
Monitor serum sodium every 2 hours during initial correction for severe symptoms 1. Once symptoms improve, transition to slower correction rates and address the underlying cause 1.
Common Pitfalls to Avoid
Overly rapid correction exceeding 8 mmol/L in 24 hours causes osmotic demyelination syndrome, manifesting as dysarthria, dysphagia, dysphagia, lethargy, spastic quadriparesis, seizures, coma, or death, typically 2-7 days after rapid correction 1, 7, 3. In susceptible patients with malnutrition, alcoholism, or advanced liver disease, slower rates are mandatory 7.
Inadequate monitoring during active correction leads to unrecognized overcorrection 1. Failing to identify and treat the underlying cause results in recurrent hyponatremia 1. Using fluid restriction in cerebral salt wasting worsens outcomes - this condition requires volume and sodium replacement, not restriction 1. Ignoring mild hyponatremia (130-135 mmol/L) as clinically insignificant is dangerous, as even mild hyponatremia increases fall risk (21% vs 5%) and mortality (60-fold increase with sodium <130 mmol/L) 1, 5.