Treatment of Hypernatremia with D5W in a 47kg Patient
For a 47kg patient with sodium of 164 mEq/L, initiate D5W at approximately 100 mL/hour, adjusting to correct the sodium deficit over 48-72 hours to avoid cerebral edema from overly rapid correction.
Calculation of Water Deficit and Correction Rate
The free water deficit should be calculated and replaced gradually over 48-72 hours to prevent osmotic demyelination. 1
Water deficit formula: Free water deficit = 0.6 × body weight (kg) × [(current Na/140) - 1]
For this 47kg patient: 0.6 × 47 × [(164/140) - 1] = 4.8 liters deficit 1
Target correction rate: Sodium should decrease no faster than 8-10 mEq/L per 24 hours 2, 3
Optimal timeframe: Replace the calculated deficit over 48-72 hours 1
Specific D5W Infusion Rate
Start D5W at 100 mL/hour as the baseline maintenance rate, then adjust based on serial sodium monitoring. 4
- The standard D5W maintenance rate is approximately 100 mL/kg per 24 hours, which translates to roughly 100 mL/hour for fluid maintenance 4
- For a 47kg patient requiring aggressive free water replacement, the initial rate should be 100-150 mL/hour 4
- This provides approximately 2.4-3.6 liters over 24 hours, addressing roughly half the water deficit in the first day 1
Critical Monitoring Parameters
Check serum sodium every 2-4 hours initially to ensure correction rate does not exceed 8-10 mEq/L per 24 hours. 2, 3
- Blood glucose must be monitored every 1-2 hours when initiating D5W infusions 4
- If sodium drops too rapidly (>10 mEq/L in 24 hours), reduce the D5W infusion rate 2
- If sodium correction is inadequate, increase D5W rate by 25-50 mL/hour increments 1
Algorithmic Approach to Rate Adjustment
Hour 0: Start D5W at 100 mL/hour 4
Hour 4: Recheck sodium
- If sodium decreased by 2-3 mEq/L → continue current rate 2
- If sodium decreased by <1 mEq/L → increase to 125-150 mL/hour 1
- If sodium decreased by >4 mEq/L → decrease to 75 mL/hour 2
Hour 8-12: Recheck sodium and adjust accordingly to maintain correction rate of 0.3-0.5 mEq/L per hour (8-12 mEq/L per 24 hours) 2, 1
Critical Pitfalls to Avoid
Too rapid correction (>10-12 mEq/L per 24 hours) can cause fatal cerebral edema, particularly in chronic hypernatremia. 1, 3
- Extreme hypernatremia (>190 mEq/L) has been associated with fatal arrhythmias including QT prolongation and ventricular tachycardia 3
- In this patient with Na 164 mEq/L, the risk of cerebral edema from overly rapid correction outweighs the immediate cardiac risk 1
- Monitor for signs of cerebral edema: worsening mental status, seizures, or neurological deterioration during correction 1, 3
Additional Considerations
If the patient has cardiac or renal compromise, limit D5W to 100 mL/hour or less and monitor closely for fluid overload. 4
- Consider adding loop diuretics if hypervolemic hypernatremia is present, though this requires careful calculation to ensure negative sodium balance exceeds negative water balance 5
- Free water can also be administered via nasogastric tube (if patient can tolerate) to supplement IV D5W 6
- Desmopressin may be considered if diabetes insipidus is contributing to hypernatremia 6