D5W Requirements in Hypernatremia Management
For treating hypernatremia, D5W (5% dextrose in water) should be administered at a rate that corrects the free water deficit while ensuring the serum sodium decreases by no more than 8 mEq/L per 24 hours to prevent osmotic demyelination syndrome.
Understanding D5W in Hypernatremia
D5W is a hypotonic solution that provides free water once the dextrose is metabolized, making it an appropriate choice for hypernatremia correction. When administered:
- D5W contains 50g of dextrose per liter (5%)
- After dextrose metabolism, it effectively becomes free water
- The osmolarity of D5W is 278 mOsm/L before dextrose metabolism
- After metabolism, it has an osmolarity of 0 mOsm/L, functioning as pure water
Calculating Free Water Deficit
To determine the appropriate amount of D5W needed, calculate the free water deficit:
Free Water Deficit = Total Body Water × [(Current Na⁺/Desired Na⁺) - 1]
Where:
- Total Body Water (TBW) = 0.6 × weight (kg) for men or 0.5 × weight (kg) for women
- Current Na⁺ = measured serum sodium
- Desired Na⁺ = target serum sodium
Administration Guidelines
Rate of Correction
- Maximum rate of sodium correction: 4-6 mEq/L per 24 hours, not exceeding 8 mEq/L per 24 hours 1
- For chronic hypernatremia (>48 hours), correct more slowly over 48-72 hours 2
- For acute hypernatremia (<48 hours), correction can be more rapid but still controlled
Volume Administration
- Calculate the hourly rate by dividing the free water deficit by the planned correction period (48-72 hours)
- Monitor serum sodium every 2-4 hours during initial treatment 1
- Adjust the rate as needed based on sodium measurements
Special Considerations
Hypervolemic Hypernatremia
- In hypervolemic states, combine D5W with diuretics to achieve negative sodium and potassium balance while correcting free water deficit 3
- The goal is to ensure negative Na⁺ and K⁺ balance exceeds negative water balance
Hyperglycemic States with Hypernatremia
- In cases of hyperglycemic hyperosmolar state with hypernatremia, D5W can be used after initial blood glucose reduction to <300 mg/dL 4, 5
- For diabetic patients, once serum glucose reaches 250 mg/dL, change fluid to D5W with appropriate sodium concentration (0.2-0.45% NaCl) 4
Monitoring Requirements
- Check serum sodium every 2 hours initially, then every 4 hours during treatment 1
- Monitor for signs of cerebral edema (headache, altered mental status, seizures)
- Assess volume status frequently
- Monitor potassium levels as correction progresses
Pitfalls to Avoid
- Too rapid correction: Can cause cerebral edema and neurological deterioration
- Too slow correction: Prolonged hypernatremia can lead to continued neurological symptoms
- Failure to account for ongoing losses: Adjust calculations for continued water losses
- Ignoring volume status: Treatment approach differs for hypovolemic, euvolemic, and hypervolemic hypernatremia
- Overlooking concurrent electrolyte abnormalities: Address potassium, calcium, and magnesium imbalances
By carefully calculating free water deficit and administering D5W at an appropriate rate with close monitoring, hypernatremia can be safely and effectively corrected while minimizing the risk of complications.