Treatment of Hypovolemic Hyponatremia
For hypovolemic hyponatremia, discontinue diuretics immediately and administer isotonic saline (0.9% NaCl) for volume repletion, with correction not exceeding 8 mmol/L in 24 hours. 1
Initial Assessment and Diagnosis
Before initiating treatment, confirm hypovolemic status through clinical examination:
- Look for orthostatic hypotension, dry mucous membranes, decreased skin turgor, and flat neck veins 1
- Check urine sodium <30 mmol/L, which has a 71-100% positive predictive value for response to saline infusion 1, 2
- Measure serum and urine osmolality, urine electrolytes, and assess extracellular fluid volume status 1
The most common causes of hypovolemic hyponatremia include gastrointestinal losses (vomiting, diarrhea), excessive diuretic use, burns, and dehydration. 3, 4
Primary Treatment Approach
Administer isotonic saline (0.9% NaCl) for volume repletion: 1, 5, 3
- Initial infusion rate: 15-20 mL/kg/h 1
- Subsequent rates: 4-14 mL/kg/h based on clinical response 1
- Continue until clinical euvolemia is achieved (absence of orthostatic hypotension, normal skin turgor, moist mucous membranes, stable vital signs) 1
Immediately discontinue any diuretics, especially if sodium <125 mmol/L 1, 5
Critical Correction Rate Guidelines
The single most important safety principle is avoiding overly rapid correction:
- Standard correction rate: Maximum 8 mmol/L in 24 hours 1, 2, 5
- For high-risk patients (advanced liver disease, alcoholism, malnutrition, prior encephalopathy): 4-6 mmol/L per day, maximum 8 mmol/L in 24 hours 1, 2
- For severe symptomatic hyponatremia: Correct 6 mmol/L over first 6 hours or until symptoms resolve, then limit total to 8 mmol/L in 24 hours 1, 2
Exceeding these limits risks osmotic demyelination syndrome, a devastating neurological complication that can cause dysarthria, dysphagia, quadriparesis, or death. 1, 2
Monitoring Protocol
Check serum sodium levels: 1
- Every 2 hours during initial correction for severe symptoms 1
- Every 4 hours after resolution of severe symptoms 1
- Every 24-48 hours once stable 1
Monitor for signs of euvolemia: absence of orthostatic hypotension, normal skin turgor, moist mucous membranes, and stable vital signs 1
Special Considerations
Avoid hypotonic fluids (0.45% saline, D5W) as they can worsen hyponatremia 1, 5
Do not use lactated Ringer's solution - it is slightly hypotonic (130 mEq/L sodium, 273 mOsm/L) and was not studied in hyponatremia prevention trials 1
Once euvolemic, switch to maintenance isotonic fluids at 30 mL/kg/day for adults 1
Common Pitfalls to Avoid
- Never correct chronic hyponatremia faster than 8 mmol/L in 24 hours - this causes osmotic demyelination syndrome 1, 2
- Do not use fluid restriction in hypovolemic hyponatremia - this worsens the underlying volume depletion 1, 4
- Inadequate monitoring during active correction can lead to overcorrection 1
- Failing to discontinue causative diuretics perpetuates the problem 1, 5
Management of Overcorrection
If sodium correction exceeds 8 mmol/L in 24 hours: 1
- Immediately discontinue current fluids and switch to D5W (5% dextrose in water) 1
- Consider administering desmopressin to slow or reverse the rapid rise 1
- Watch for signs of osmotic demyelination syndrome (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically occurring 2-7 days after rapid correction 1