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The 4-2-1 Rule (Holliday-Segar Method)
The 4-2-1 rule is the standard method for calculating hourly maintenance intravenous fluid rates for children and adults. It estimates water loss based on caloric expenditure.
- First 10 kg 4 mL/kg/hr
- Next 10 kg (11-20 kg) 2 mL/kg/hr
- Each kg over 20 kg 1 mL/kg/hr
Example Calculation
Patient: A 25 kg child requires maintenance fluids.
Step 1 (First 10 kg): 10 kg × 4 mL/kg/hr = 40 mL/hr
Step 2 (Next 10 kg): 10 kg × 2 mL/kg/hr = 20 mL/hr
Step 3 (Remaining 5 kg): 5 kg × 1 mL/kg/hr = 5 mL/hr
Total Rate: 40 + 20 + 5 = 65 mL/hr
Important Considerations
- Maximum Rates: In adults, maintenance fluids are often capped at 100-120 mL/hr depending on clinical status.
- Fluid Type: Isotonic fluids (e.g., 0.9% Normal Saline or Plasmalyte) are generally preferred for maintenance to prevent hyponatremia.
- Adjustments: Increase for fever, sweating, burns, or vomiting. Decrease for heart failure, renal failure, or oliguria.
How to Use
Input the patient's weight. The tool applies the 4-2-1 rule to calculate the hourly maintenance IV fluid rate.
Case Example
Patient: A child weighing 25 kg requiring maintenance fluids.
Calculation: First 10 kg: 40 mL. Next 10 kg: 20 mL. Remaining 5 kg: 5 * 1 = 5 mL. Total = 40 + 20 + 5 = 65 mL/hr.
Interpretation: Set the pump to 65 mL/hr for standard maintenance fluids.
Frequently Asked Questions
It calculates hourly fluid needs: 4 mL/kg/hr for the first 10 kg, 2 mL/kg/hr for the next 10 kg, and 1 mL/kg/hr for every kg above 20 kg.
For large adults, the 4-2-1 rule can result in very high rates. Typically, adult maintenance fluids are capped around 100-150 mL/hr depending on clinical status.