What rate of D5W (Dextrose 5% in Water) is needed to correct hypernatremia from 132 to 128 mmol/L in 6 hours?

Calculating D5W Rate to Lower Overcorrected Sodium from 132 to 128 mmol/L in 6 Hours

To lower sodium from 132 to 128 mmol/L over 6 hours, administer D5W at approximately 3 mL/kg/hour, which translates to roughly 200-250 mL/hour for a 70 kg patient. This approach prevents osmotic demyelination syndrome while achieving controlled relowering of overcorrected sodium 1.

Understanding the Clinical Context

When sodium has been overcorrected beyond the safe limit of 8 mmol/L in 24 hours, immediate intervention with D5W is critical to prevent osmotic demyelination syndrome 1. The goal is to bring the total 24-hour correction back within safe parameters by actively relowering the sodium level 1.

Calculation Method

Step 1: Determine Required Sodium Decrease

• Target decrease: 4 mmol/L (from 132 to 128 mmol/L) over 6 hours 1
• This represents a correction rate of approximately 0.67 mmol/L/hour 1

Step 2: Calculate Free Water Deficit

• Use the formula: Desired decrease in Na (mEq/L) × (0.5 × body weight in kg) 1
• For a 70 kg patient: 4 mEq/L × (0.5 × 70 kg) = 140 mEq sodium needs to be diluted 1
• This requires approximately 1.4-1.8 liters of free water over 6 hours 2

Step 3: Determine D5W Infusion Rate

• For a 70 kg patient: 1.4-1.8 L ÷ 6 hours = 233-300 mL/hour 2
• Weight-based calculation: approximately 3-4 mL/kg/hour 2
• Start with 3 mL/kg/hour and adjust based on hourly sodium monitoring 1

Monitoring Requirements

• Check serum sodium every 2 hours during active relowering 1
• Adjust D5W rate if sodium decreases too rapidly or too slowly 1
• Target is to achieve 128 mmol/L within the 6-hour window without overshooting 1

Special Considerations for High-Risk Patients

Patients with Advanced Liver Disease or Malnutrition

• These patients require even more cautious correction, with maximum rates of 4-6 mmol/L per day 1
• Consider slower relowering over 8-12 hours rather than 6 hours 1

Patients with Renal Failure on CRRT

• D5W can be administered prefilter to prevent overcorrection while maintaining adequate effluent volumes 2
• Calculate D5W rate based on prescribed effluent volume to maintain sodium correction within safe limits 2

Adjunctive Therapy

Consider administering desmopressin (2-4 mcg IV or SC) to slow or reverse the rapid rise in serum sodium 1. This can be particularly helpful when overcorrection has occurred rapidly and additional pharmacologic intervention is needed beyond D5W alone 1.

Common Pitfalls to Avoid

• Failing to discontinue hypertonic saline immediately when overcorrection is recognized - this delays appropriate intervention 1
• Not monitoring sodium levels frequently enough - hourly or every 2 hours is essential during active relowering 1
• Underestimating free water requirements - err on the side of slightly faster D5W rates with close monitoring rather than inadequate correction 2
• Forgetting to account for ongoing fluid losses - adjust D5W rate upward if patient has continued losses from diuretics or other sources 1

Alternative Approach for Patients Unable to Tolerate Large Volumes

For patients with heart failure or cirrhosis who cannot tolerate large fluid volumes, consider using D5W at a slower rate (1-2 mL/kg/hour) combined with desmopressin to achieve the target sodium decrease over 8-12 hours instead of 6 hours 1. This reduces the risk of volume overload while still preventing osmotic demyelination syndrome 1.