Hyponatremia Management Algorithm
Initial Assessment and Classification
Hyponatremia should be evaluated systematically based on volume status, symptom severity, and serum osmolality when serum sodium is <135 mmol/L, with full workup initiated when sodium drops below 131 mmol/L. 1
Step 1: Determine Volume Status
- Hypovolemic signs: Orthostatic hypotension, dry mucous membranes, decreased skin turgor, flat neck veins 1
- Euvolemic signs: No edema, normal blood pressure, normal skin turgor, moist mucous membranes 1
- Hypervolemic signs: Peripheral edema, ascites, jugular venous distention, pulmonary congestion 1
Step 2: Obtain Essential Laboratory Tests
- 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 1
Step 3: Classify Symptom Severity
- Severe symptoms (medical emergency): Seizures, coma, confusion, altered consciousness, respiratory distress 1, 2
- Moderate symptoms: Nausea, vomiting, headache, muscle cramps, lethargy 2
- Mild/asymptomatic: Minimal or no symptoms 1
Treatment Based on Symptom Severity
SEVERE SYMPTOMATIC HYPONATREMIA (Emergency)
For patients with seizures, coma, or altered mental status, immediately administer 3% hypertonic saline with a target correction of 6 mmol/L over 6 hours or until severe symptoms resolve. 1
- Initial bolus: 100 mL of 3% saline over 10 minutes, can repeat up to 3 times at 10-minute intervals 1
- Maximum correction: 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome 1
- Monitoring: Check serum sodium every 2 hours during initial correction 1
- ICU admission: Required for close monitoring during treatment 1
Treatment Based on Volume Status
HYPOVOLEMIC HYPONATREMIA
Discontinue diuretics and administer isotonic saline (0.9% NaCl) for volume repletion. 1
- Diagnostic criteria: Urine sodium <30 mmol/L (71-100% positive predictive value for saline response) 1
- Initial infusion rate: 15-20 mL/kg/h, then 4-14 mL/kg/h based on response 1
- Correction limit: Maximum 8 mmol/L in 24 hours 1
- Once euvolemic: Reassess and adjust management based on underlying cause 1
EUVOLEMIC HYPONATREMIA (SIADH)
Fluid restriction to 1 L/day is the cornerstone of treatment for SIADH. 1
For Mild/Asymptomatic Cases:
- Primary treatment: Fluid restriction to 1000 mL/day 1
- If no response: Add oral sodium chloride 100 mEq three times daily 1
- Alternative options: Urea, demeclocycline, lithium, loop diuretics 1
For Severe Symptomatic Cases:
- Immediate treatment: 3% hypertonic saline as described above 1
- After symptom resolution: Transition to fluid restriction 1
Pharmacological Options for Resistant Cases:
- Tolvaptan: Starting dose 15 mg once daily, titrate based on response 1
- Caution: Monitor closely to avoid overly rapid correction (>8 mmol/L/day) 3
- Adverse effects: Thirst, dry mouth, polyuria 3
HYPERVOLEMIC HYPONATREMIA (Heart Failure, Cirrhosis)
Implement fluid restriction to 1-1.5 L/day for serum sodium <125 mmol/L. 1
Management Steps:
- Fluid restriction: 1000-1500 mL/day 1
- Discontinue diuretics: Temporarily if sodium <125 mmol/L 1
- For cirrhotic patients: Consider albumin infusion (6-8 g per liter of ascites drained) 1
- Avoid hypertonic saline: Unless life-threatening symptoms present, as it worsens edema and ascites 1
Pharmacological Considerations:
- Vaptans: May be considered for persistent severe hyponatremia despite fluid restriction 1
- Cirrhosis warning: Tolvaptan carries 10% risk of gastrointestinal bleeding vs. 2% with placebo 1, 3
Special Populations and High-Risk Considerations
Patients with Advanced Liver Disease, Alcoholism, or Malnutrition
These patients require more cautious correction at 4-6 mmol/L per day, not exceeding 8 mmol/L in 24 hours, due to higher risk of osmotic demyelination syndrome. 1
Neurosurgical Patients: Distinguishing SIADH from Cerebral Salt Wasting (CSW)
In neurosurgical patients, cerebral salt wasting is more common than SIADH and requires fundamentally different treatment. 1
SIADH Characteristics:
- Euvolemic state 1
- Urine sodium >20-40 mmol/L 1
- Urine osmolality >300 mOsm/kg 1
- Treatment: Fluid restriction 1
CSW Characteristics:
- True hypovolemia with CVP <6 cm H₂O 1
- Urine sodium >20 mmol/L despite volume depletion 1
- Evidence of extracellular volume depletion 1
- Treatment: Volume and sodium replacement with isotonic or hypertonic saline 1
- For severe symptoms: 3% hypertonic saline plus fludrocortisone (0.1-0.2 mg daily) 1
Critical Warning for Neurosurgical Patients:
- Never use fluid restriction in CSW as it worsens outcomes 1
- Avoid fluid restriction in subarachnoid hemorrhage patients at risk of vasospasm 1
- Consider fludrocortisone or hydrocortisone to prevent natriuresis 1
Critical Correction Rate Guidelines
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
- Never exceed: 8 mmol/L in 24 hours for chronic hyponatremia 1
Monitoring During Correction:
- Severe symptoms: Every 2 hours initially 1
- After symptom resolution: Every 4 hours 1
- Stable patients: Daily monitoring 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
- Consider desmopressin: To slow or reverse rapid rise in serum sodium 1
- Target: Bring total 24-hour correction to no more than 8 mmol/L from starting point 1
- Watch for osmotic demyelination syndrome: Dysarthria, dysphagia, oculomotor dysfunction, quadriparesis typically occurring 2-7 days after rapid correction 1
Common Pitfalls to Avoid
- Ignoring mild hyponatremia (130-135 mmol/L): Even mild chronic hyponatremia increases fall risk (21% vs. 5%) and mortality (60-fold increase) 1, 2
- Overly rapid correction: Exceeding 8 mmol/L in 24 hours risks osmotic demyelination syndrome 1
- Using fluid restriction in CSW: Worsens outcomes in neurosurgical patients 1
- Inadequate monitoring during active correction: Can lead to overcorrection 1
- Using hypertonic saline in hypervolemic hyponatremia: Without life-threatening symptoms worsens edema 1
- Failing to recognize underlying cause: Delays appropriate treatment 1
Sodium Deficit Calculation
Formula: Sodium deficit (mEq) = Desired increase in Na (mEq/L) × (0.5 × ideal body weight in kg) 1