Management 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 to prevent osmotic demyelination syndrome. 1
Initial Assessment
Hypovolemic hyponatremia occurs when both sodium and water are lost, but water loss is proportionally less than sodium loss. 2 The key diagnostic features include:
- Clinical signs of volume depletion: orthostatic hypotension, dry mucous membranes, decreased skin turgor, flat neck veins 1
- Urine sodium <30 mmol/L has a 71-100% positive predictive value for response to saline infusion 1
- Low serum osmolality with inappropriately concentrated urine 1
Common causes include gastrointestinal losses (vomiting, diarrhea), excessive diuretic use, burns, and third-spacing of fluids. 3
Treatment Algorithm
Step 1: Immediate Interventions
- Stop all diuretics immediately if sodium is <125 mmol/L 1
- Begin isotonic saline (0.9% NaCl) for volume repletion 1, 2
- Initial infusion rate: 15-20 mL/kg/h, then adjust to 4-14 mL/kg/h based on clinical response 1
Step 2: Determine Symptom Severity
For severe symptoms (seizures, coma, altered mental status):
- Administer 3% hypertonic saline with initial goal to correct 6 mmol/L over 6 hours or until severe symptoms resolve 1
- Monitor serum sodium every 2 hours during initial correction 1
- Consider ICU admission for close monitoring 1
For mild/asymptomatic cases:
- Continue isotonic saline until euvolemia is achieved 1
- Monitor sodium levels every 4-6 hours initially 1
Step 3: Critical Correction Rate Guidelines
Standard correction limits (most patients):
High-risk patients (cirrhosis, alcoholism, malnutrition, prior encephalopathy):
Special Considerations
Severe Dehydration with Neurological Symptoms
For patients with severe volume depletion and neurological symptoms, consider hypertonic saline with careful monitoring, but transition to isotonic saline once symptoms improve. 1 The priority is reversing life-threatening symptoms while avoiding overcorrection.
Diuretic-Induced Hyponatremia
This is a particularly common cause in clinical practice. 5 The combination of sodium loss from diuretics plus free water intake creates the perfect storm for hypovolemic hyponatremia. Immediate diuretic cessation is essential. 1
Monitoring During Correction
- Check sodium every 2 hours for severe symptoms 1
- Check sodium every 4 hours after symptom resolution 1
- Once stable, transition to daily monitoring 1
Common Pitfalls to Avoid
Overly rapid correction exceeding 8 mmol/L in 24 hours leads to osmotic demyelination syndrome, which can cause dysarthria, dysphagia, oculomotor dysfunction, quadriparesis, or death. 1, 4 This typically occurs 2-7 days after rapid correction. 1
Using hypotonic fluids (like lactated Ringer's) can worsen hyponatremia through dilution and should be avoided. 1 Lactated Ringer's has only 130 mEq/L sodium and is slightly hypotonic (273 mOsm/L). 1
Inadequate monitoring during active correction is dangerous—frequent sodium checks are mandatory, not optional. 1
Failing to discontinue diuretics when sodium drops below 125 mmol/L perpetuates the problem. 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 administering desmopressin to slow or reverse the rapid rise 1
- The goal is to bring total 24-hour correction to no more than 8 mmol/L from the starting point 1
Calculating Sodium Deficit
Use the formula: Desired increase in Na (mEq/L) × (0.5 × ideal body weight in kg) 1
This helps determine the appropriate amount of sodium supplementation needed, though clinical response and frequent monitoring should guide ongoing management rather than relying solely on calculations. 1