Initial Approach to Treating Hyponatremia
The initial approach to treating hyponatremia must be determined by assessing symptom severity, volume status (hypovolemic, euvolemic, or hypervolemic), and serum osmolality, with immediate 3% hypertonic saline reserved for severe symptomatic cases and tailored management based on the underlying etiology for all others. 1
Step 1: Assess Symptom Severity and Urgency
Severe symptomatic hyponatremia (seizures, coma, altered consciousness, respiratory distress) constitutes a medical emergency requiring immediate intervention 1, 2:
- Administer 3% hypertonic saline immediately as 100 mL boluses over 10 minutes, repeatable up to three times at 10-minute intervals 1
- Target correction of 6 mmol/L over 6 hours or until severe symptoms resolve 1
- Never exceed 8 mmol/L correction in 24 hours to prevent osmotic demyelination syndrome 1
- Monitor serum sodium every 2 hours during initial correction 1
Mild to moderate symptoms (nausea, vomiting, headache, lethargy, muscle cramps) or asymptomatic hyponatremia require a more measured approach based on volume status 2, 3.
Step 2: Determine Volume Status and Serum Osmolality
Perform focused physical examination looking for specific signs 1:
Hypovolemic indicators:
- Orthostatic hypotension, dry mucous membranes, decreased skin turgor, flat neck veins 1
- Urine sodium <30 mmol/L predicts saline responsiveness with 71-100% positive predictive value 1
Euvolemic indicators:
- No edema, normal blood pressure, moist mucous membranes 1
- Urine sodium >20-40 mmol/L with urine osmolality >300 mOsm/kg suggests SIADH 1
Hypervolemic indicators:
- Peripheral edema, ascites, jugular venous distention 1
Obtain serum and urine osmolality, urine sodium, and uric acid to determine underlying cause 1.
Step 3: Initiate Treatment Based on Volume Status
For Hypovolemic Hyponatremia:
- Discontinue diuretics immediately 1
- Administer isotonic saline (0.9% NaCl) for volume repletion 1
- Correct at 4-8 mmol/L per day, maximum 8 mmol/L in 24 hours 1
For Euvolemic Hyponatremia (SIADH):
- Fluid restriction to 1 L/day is the cornerstone of treatment 1
- If no response after 24-48 hours, add oral sodium chloride 100 mEq three times daily 1
- For severe symptoms, use 3% hypertonic saline as described above 1
- Consider urea or tolvaptan for resistant cases 1, 4
For Hypervolemic Hyponatremia (heart failure, cirrhosis):
- Fluid restriction to 1-1.5 L/day for sodium <125 mmol/L 1
- Discontinue diuretics temporarily if sodium <125 mmol/L 1
- Consider albumin infusion in cirrhotic patients 1
- Avoid hypertonic saline unless life-threatening symptoms present, as it worsens edema and ascites 1
Step 4: Special Populations Requiring Cautious Correction
High-risk patients (advanced liver disease, alcoholism, malnutrition, prior encephalopathy) require even slower correction at 4-6 mmol/L per day, maximum 8 mmol/L in 24 hours due to increased risk of osmotic demyelination syndrome 1.
Neurosurgical patients require distinction between SIADH and cerebral salt wasting (CSW) 1:
- CSW requires volume and sodium replacement, not fluid restriction 1
- Consider fludrocortisone 0.1-0.2 mg daily for severe CSW 1
- Never use fluid restriction in subarachnoid hemorrhage patients at risk of vasospasm 1
Critical Pitfalls to Avoid
- Never correct chronic hyponatremia faster than 8 mmol/L in 24 hours - this causes osmotic demyelination syndrome 1
- Never use fluid restriction in cerebral salt wasting - this worsens outcomes 1
- Never ignore mild hyponatremia (130-135 mmol/L) - it increases fall risk 60-fold and mortality 1, 2
- Never use hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms 1
- Avoid lactated Ringer's solution - it is hypotonic (273 mOsm/L) and can worsen hyponatremia 1