Why the Modified Parkland Formula is Divided by 16 to Find the Hourly Rate
The modified Parkland formula is divided by 16 to calculate the hourly fluid rate because half of the total 24-hour fluid requirement is administered in the first 8 hours (8 hours), and the remaining half is given over the next 16 hours (16 hours).
Understanding the Parkland Formula
The Parkland formula is a widely used method for calculating fluid resuscitation requirements in burn patients:
- The standard Parkland formula recommends 4 mL/kg/%TBSA (Total Body Surface Area burned) for the first 24 hours 1
- Half of this calculated volume should be given in the first 8 hours post-burn 2
- The remaining half is administered over the following 16 hours 2
Mathematical Breakdown of the Hourly Rate Calculation
When calculating the hourly fluid rate for the second half of resuscitation (hours 9-24):
- Total 24-hour fluid volume = 4 mL/kg/%TBSA
- Second half volume (for hours 9-24) = 2 mL/kg/%TBSA
- This second half is administered over 16 hours
- Therefore, hourly rate = 2 mL/kg/%TBSA ÷ 16 hours = 0.125 mL/kg/%TBSA per hour 1
Clinical Implementation
The division by 16 ensures proper distribution of fluids during the critical second phase of resuscitation:
- For the first 8 hours: Half the total volume ÷ 8 hours = 0.25 mL/kg/%TBSA per hour 2
- For the next 16 hours: Half the total volume ÷ 16 hours = 0.125 mL/kg/%TBSA per hour 1
Importance of Proper Fluid Rate Calculation
Accurate hourly rate calculation is crucial for several reasons:
- Prevents "fluid creep" - excessive fluid administration that can lead to complications 3
- Ensures adequate tissue perfusion while avoiding overhydration 4
- Helps maintain appropriate urine output (target 0.5-1.0 mL/kg/hr) 4
Common Pitfalls in Fluid Resuscitation
- Failure to adjust the infusion rate after the first 8 hours can lead to excessive fluid administration 3
- Using the same hourly rate throughout the 24-hour period would deliver too much fluid during the second phase 3
- Not recognizing that the physiologic need for fluid decreases after the first 8 hours post-burn 5
Evidence Supporting This Approach
Research has shown that the Parkland formula often serves as a starting point, with actual fluid needs varying based on clinical response:
- Studies show that patients frequently receive more fluid than calculated by the formula 4
- The most important parameter for guiding fluid therapy is urine output, not rigid adherence to calculated volumes 4
- Central hemodynamic monitoring shows that the standard Parkland volumes are generally adequate when properly administered 5
By dividing the second half of the fluid requirement by 16, clinicians can provide a physiologically appropriate fluid rate that accounts for the changing needs of burn patients during the resuscitation period.