Initial Approach to Treating Hyponatremia
The initial approach to treating hyponatremia must be determined by symptom severity first, then volume status—with severe symptoms requiring immediate 3% hypertonic saline regardless of volume status, while asymptomatic or mildly symptomatic cases require volume status assessment to guide therapy. 1
Step 1: Assess Symptom Severity (This Determines Urgency)
Severe symptoms constitute a medical emergency and include seizures, coma, altered consciousness, confusion, delirium, or respiratory distress 1, 2. These patients require immediate treatment regardless of sodium level or volume status 3.
Mild to moderate symptoms include nausea, vomiting, headache, muscle cramps, lethargy, weakness, gait instability, and dizziness 2. These patients can be managed more gradually based on volume status 1.
Asymptomatic patients still require treatment, as even mild chronic hyponatremia (130-135 mEq/L) increases mortality 60-fold and significantly increases fall risk 1, 2.
Step 2: Initial Management Based on Symptom Severity
For Severe Symptomatic Hyponatremia (Medical Emergency)
Administer 100 mL of 3% hypertonic saline IV over 10 minutes immediately 3. This can be repeated every 10 minutes up to three total boluses if symptoms persist 3.
- Target correction: 6 mmol/L over 6 hours or until severe symptoms resolve 1, 3
- Critical safety limit: Never exceed 8 mmol/L correction in 24 hours to prevent osmotic demyelination syndrome 1, 3
- Monitoring: Check serum sodium every 2 hours during initial correction 1, 3
For Asymptomatic or Mildly Symptomatic Hyponatremia
Proceed to volume status assessment before initiating treatment 1.
Step 3: Assess Volume Status (For Non-Emergency Cases)
Perform physical examination looking for specific findings 1:
Hypovolemic signs: Orthostatic hypotension, dry mucous membranes, decreased skin turgor, flat neck veins 1
Euvolemic signs: No edema, no orthostatic hypotension, normal skin turgor, moist mucous membranes 1
Hypervolemic signs: Peripheral edema, ascites, jugular venous distention, pulmonary congestion 1
Step 4: Obtain Essential Laboratory Tests
Immediately obtain 1:
- Serum osmolality (to exclude pseudohyponatremia)
- Urine osmolality
- Urine sodium concentration
- Serum uric acid (if <4 mg/dL, suggests SIADH with 73-100% positive predictive value) 1
Step 5: Treatment Based on Volume Status
Hypovolemic Hyponatremia
Discontinue diuretics immediately and administer isotonic saline (0.9% NaCl) for volume repletion 1. Urine sodium <30 mmol/L predicts good response to saline with 71-100% positive predictive value 1.
Euvolemic Hyponatremia (SIADH)
Fluid restriction to 1 L/day is the cornerstone of treatment 1, 3. If no response to fluid restriction, add oral sodium chloride 100 mEq three times daily 1, 3. For severe symptoms, use 3% hypertonic saline with careful monitoring 1.
Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)
Implement fluid restriction to 1-1.5 L/day for sodium <125 mmol/L 1. Discontinue diuretics temporarily 1. Consider albumin infusion in cirrhotic patients 1. Avoid hypertonic saline unless life-threatening symptoms are present, as it worsens edema and ascites 1.
Critical Correction Rate Guidelines
Standard correction rate: 4-8 mmol/L per day, maximum 8 mmol/L in 24 hours 1
High-risk patients (advanced liver disease, alcoholism, malnutrition, prior encephalopathy) require even slower correction: 4-6 mmol/L per day, maximum 8 mmol/L in 24 hours 1, 3
Common Pitfalls to Avoid
- Never exceed 8 mmol/L correction in 24 hours—this causes osmotic demyelination syndrome 1, 3
- Never use fluid restriction in cerebral salt wasting—this worsens outcomes 1
- Never ignore mild hyponatremia (130-135 mmol/L)—it significantly increases mortality and fall risk 1, 2
- Never use hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms—it worsens fluid overload 1
- In neurosurgical patients, distinguish SIADH from cerebral salt wasting—they require opposite treatments (fluid restriction vs. volume replacement) 1, 3