Hyponatremia Management
Initial Assessment and Classification
Hyponatremia (serum sodium <135 mmol/L) requires immediate evaluation based on symptom severity, volume status, and serum osmolality to guide treatment and prevent serious complications including osmotic demyelination syndrome. 1
Severity Classification
- Mild: 130-135 mmol/L 2
- Moderate: 125-129 mmol/L (120-125 mmol/L per some guidelines) 1, 2
- Severe: <120-125 mmol/L 1, 2
Critical Initial Workup
- Serum and urine osmolality 1
- Urine sodium concentration 1
- Urine electrolytes 1
- Serum uric acid (levels <4 mg/dL suggest SIADH with 73-100% positive predictive value) 1
- Assessment of extracellular fluid volume status through physical examination (orthostatic hypotension, dry mucous membranes, skin turgor, jugular venous distention, peripheral edema, ascites) 1
Treatment Based on Symptom Severity
Severe Symptomatic Hyponatremia (Medical Emergency)
For patients with severe symptoms (seizures, coma, confusion, altered mental status), immediately administer 3% hypertonic saline with a target correction of 6 mmol/L over 6 hours or until symptoms resolve. 1, 2, 3
- Administration: 100-150 mL bolus of 3% hypertonic saline over 10 minutes, repeatable up to three times at 10-minute intervals 1
- Target: Increase sodium by 4-6 mEq/L within first 1-2 hours 3
- Critical limit: Total correction must NOT exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome 1, 3
- Monitoring: Check serum sodium every 2 hours during initial correction 1
- ICU admission: Required for close monitoring 1
Asymptomatic or Mildly Symptomatic Hyponatremia
Treatment depends on volume status classification:
Treatment Based on Volume Status
Hypovolemic Hyponatremia
Discontinue diuretics immediately and administer isotonic saline (0.9% NaCl) for volume repletion. 1, 2
- Diagnostic clue: Urine sodium <30 mmol/L has 71-100% positive predictive value for saline responsiveness 1
- Initial infusion rate: 15-20 mL/kg/h, then 4-14 mL/kg/h based on response 1
- Causes: Gastrointestinal losses, diuretic use, burns, dehydration 1, 4
Euvolemic Hyponatremia (SIADH)
Fluid restriction to 1 L/day is the cornerstone of treatment for SIADH. 1, 3
- First-line: Fluid restriction <1 L/day 1, 3
- If no response: Add oral sodium chloride 100 mEq three times daily 1
- Second-line options:
Diagnostic criteria for SIADH: Hypotonic hyponatremia, urine osmolality >300 mOsm/kg, urine sodium >20-40 mmol/L, euvolemic state, normal thyroid/adrenal/renal function 1
Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)
Implement fluid restriction to 1-1.5 L/day for serum sodium <125 mmol/L and avoid hypertonic saline unless life-threatening symptoms are present. 1, 2
- Fluid restriction: 1000-1500 mL/day 1
- Discontinue diuretics temporarily if sodium <125 mmol/L 1
- For cirrhosis: Consider albumin infusion alongside fluid restriction 1
- Avoid hypertonic saline: It worsens ascites and edema unless severe symptoms present 1
- Note: Fluid restriction may prevent further decline but rarely improves sodium significantly—it is sodium restriction (not fluid restriction) that results in weight loss as fluid follows sodium 1
Critical Correction Rate Guidelines
The maximum correction rate must not exceed 8 mmol/L in 24 hours for all patients to prevent osmotic demyelination syndrome. 1, 3
Standard Correction Rates
- Average risk patients: 4-8 mmol/L per day, maximum 10-12 mmol/L in 24 hours 1
- High-risk patients: 4-6 mmol/L per day, maximum 8 mmol/L in 24 hours 1
High-Risk Populations Requiring Slower Correction (4-6 mmol/L per day)
- Advanced liver disease 1
- Alcoholism 1
- Malnutrition 1
- Prior encephalopathy 1
- Severe hyponatremia (<120 mmol/L) 1
- Hypophosphatemia, hypokalemia, hypoglycemia 1
Management of Overcorrection
If sodium correction exceeds 8 mmol/L in 24 hours, immediately discontinue current fluids and switch to D5W (5% dextrose in water). 1
- Immediate action: Stop hypertonic saline, administer D5W 1
- Consider desmopressin: To slow or reverse rapid sodium rise 1
- Goal: Bring total 24-hour correction to no more than 8 mmol/L from starting point 1
- Monitor for osmotic demyelination syndrome: Dysarthria, dysphagia, oculomotor dysfunction, quadriparesis (typically occurs 2-7 days after rapid correction) 1
Special Considerations
Cerebral Salt Wasting (CSW) in Neurosurgical Patients
CSW requires volume and sodium replacement with isotonic or hypertonic saline—NEVER fluid restriction, which worsens outcomes. 1
- Treatment: Volume and sodium replacement with normal saline or 3% hypertonic saline 1
- Severe symptoms: 3% hypertonic saline plus fludrocortisone (0.1-0.2 mg daily) in ICU 1
- Distinguishing from SIADH: CSW shows true hypovolemia (CVP <6 cm H₂O), orthostatic hypotension, dry mucous membranes despite high urine sodium >20 mmol/L 1
- Subarachnoid hemorrhage patients: Avoid fluid restriction as it increases vasospasm risk; consider fludrocortisone or hydrocortisone 1
Cirrhotic Patients
Cirrhotic patients with hyponatremia have significantly increased risk of complications and require cautious correction at 4-6 mmol/L per day. 1
- Increased risks: Spontaneous bacterial peritonitis (OR 3.40), hepatorenal syndrome (OR 3.45), hepatic encephalopathy (OR 2.36) 1
- Tolvaptan caution: Higher risk of gastrointestinal bleeding (10% vs 2% placebo) 1
- Albumin infusion: May be beneficial alongside fluid restriction 1
Common Pitfalls to Avoid
- Overly rapid correction exceeding 8 mmol/L in 24 hours causes osmotic demyelination syndrome 1
- Using fluid restriction in CSW worsens outcomes 1
- Inadequate monitoring during active correction 1
- Failing to recognize and treat underlying cause 1
- Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms 1
- Ignoring mild hyponatremia (130-135 mmol/L) which increases fall risk (21% vs 5%) and mortality (60-fold increase at <130 mmol/L) 1, 3