Management of Hyponatremia
Initial Assessment: Determine Severity and Acuity
The first critical step is to assess symptom severity and timing of onset, as this determines whether you treat aggressively or conservatively. 1
Severe Symptomatic Hyponatremia (Medical Emergency)
- Seizures, coma, altered consciousness, confusion/delirium, or respiratory distress require immediate hypertonic saline (3% NaCl) 1, 2
- Administer 100 mL boluses of 3% saline over 10 minutes, repeatable up to three times at 10-minute intervals until symptoms improve 1
- Target correction: 6 mmol/L over 6 hours or until severe symptoms resolve 1, 3
- Absolute maximum: 8 mmol/L in any 24-hour period to prevent osmotic demyelination syndrome 1, 3
- Check serum sodium every 2 hours during initial correction 1
Moderate Symptomatic Hyponatremia
- Nausea, vomiting, headache, muscle cramps, gait instability, lethargy, or dizziness 2
- Hospital admission required for monitored correction 1
- Fluid restriction to 1 L/day is first-line for euvolemic patients (SIADH) 1
- Consider oral sodium chloride 100 mEq three times daily if fluid restriction fails 1
Asymptomatic or Mildly Symptomatic
- Even mild hyponatremia (130-135 mmol/L) is not benign—it increases fall risk 4-fold (21% vs 5%) and mortality 60-fold (11.2% vs 0.19%) when <130 mmol/L 2
- Treat based on volume status and underlying cause 1
Volume Status Assessment: The Decisive Factor
Physical examination alone has poor accuracy (sensitivity 41%, specificity 80%), so combine clinical findings with laboratory data 1
Hypovolemic Hyponatremia
Clinical signs: Orthostatic hypotension, dry mucous membranes, decreased skin turgor, flat neck veins 1
Laboratory: Urine sodium <30 mmol/L (71-100% positive predictive value for saline responsiveness), elevated BUN/creatinine 1
Treatment:
- Discontinue diuretics immediately if sodium <125 mmol/L 1
- Administer isotonic saline (0.9% NaCl) at 15-20 mL/kg/h initially, then 4-14 mL/kg/h based on response 1
- Maximum correction: 8 mmol/L in 24 hours 1
Euvolemic Hyponatremia (SIADH)
Clinical signs: No edema, no orthostatic hypotension, normal skin turgor, moist mucous membranes 1
Laboratory: Urine sodium >20-40 mmol/L, urine osmolality >300 mOsm/kg, serum uric acid <4 mg/dL (73-100% positive predictive value for SIADH) 1
Treatment:
- Fluid restriction to 1 L/day is the cornerstone 1
- Add oral sodium chloride 100 mEq three times daily if no response 1
- Consider vasopressin receptor antagonists (tolvaptan 15 mg once daily, titrate to 30-60 mg) for resistant cases 1, 4
- Urea, demeclocycline, or lithium are alternative pharmacologic options 1
Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)
Clinical signs: Peripheral edema, ascites, jugular venous distention, pulmonary congestion 1
Laboratory: Urine sodium variable (often >20 mmol/L due to compensatory natriuresis) 1
Treatment:
- Fluid restriction to 1-1.5 L/day for sodium <125 mmol/L 1
- Discontinue diuretics temporarily if sodium <125 mmol/L 1
- For cirrhosis: Consider albumin infusion (6-8 g per liter of ascites drained) 1
- Avoid hypertonic saline unless life-threatening symptoms present—it worsens ascites and edema 1
- Tolvaptan may be considered for persistent severe hyponatremia despite fluid restriction, but carries higher risk of GI bleeding in cirrhosis (10% vs 2% placebo) 4
Special Populations: Neurosurgical Patients
Distinguishing SIADH from cerebral salt wasting (CSW) is critical—they require opposite treatments 1
Cerebral Salt Wasting (More Common in Neurosurgical Patients)
Diagnostic features: True hypovolemia with CVP <6 cm H₂O, urine sodium >20 mmol/L despite volume depletion, evidence of extracellular volume depletion 1
Treatment:
- Volume and sodium replacement with isotonic or hypertonic saline—NEVER fluid restriction 1
- Aggressive volume resuscitation: 50-100 mL/kg/day 1
- Fludrocortisone 0.1-0.2 mg daily for severe symptoms 1
- Hydrocortisone may prevent natriuresis in subarachnoid hemorrhage patients 1
- Fluid restriction in CSW worsens outcomes and can precipitate cerebral ischemia 1
Subarachnoid Hemorrhage Patients at Risk of Vasospasm
- Never use fluid restriction—it increases ischemic complications 1
- Consider fludrocortisone or hydrocortisone to prevent vasospasm 1
High-Risk Patients: Slower Correction Required
Patients with advanced liver disease, alcoholism, malnutrition, severe hyponatremia, or prior encephalopathy require more cautious correction (4-6 mmol/L per day, maximum 8 mmol/L in 24 hours) 1
These patients have a 0.5-1.5% risk of osmotic demyelination syndrome even with careful correction 1
Monitoring During Correction
Severe Symptoms
- Check serum sodium every 2 hours during initial correction 1
- Once severe symptoms resolve, switch to every 4 hours 3
Mild Symptoms or Asymptomatic
- Check serum sodium every 4 hours initially, then daily 1
Watch for Osmotic Demyelination Syndrome
- Typically occurs 2-7 days after rapid correction 1
- Symptoms: Dysarthria, dysphagia, oculomotor dysfunction, quadriparesis 1
Management of Overcorrection
If sodium rises >8 mmol/L in 24 hours:
- Immediately discontinue current fluids and switch to D5W (5% dextrose in water) 1
- Consider administering desmopressin to slow or reverse the rapid rise 1
- Target: Bring total 24-hour correction back to ≤8 mmol/L from baseline 1
Common Pitfalls to Avoid
- Ignoring mild hyponatremia (130-135 mmol/L) as clinically insignificant—it increases mortality and fall risk 2
- Correcting chronic hyponatremia faster than 8 mmol/L in 24 hours—this causes osmotic demyelination syndrome 1
- Using fluid restriction in cerebral salt wasting—this worsens outcomes 1
- Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms—it worsens fluid overload 1
- Failing to distinguish SIADH from CSW in neurosurgical patients—they require opposite treatments 1
- Inadequate monitoring during active correction—check sodium frequently 1
- Stopping treatment at symptom resolution without reaching target sodium of 125-130 mmol/L 5