The Maintenance Fluids Calculator uses the universally recognized Holliday-Segar "4-2-1" rule to determine the hourly intravenous (IV) fluid requirements for a patient who cannot take fluids by mouth.
Understanding Maintenance Fluids
When a patient is NPO (nothing by mouth)—for example, prior to surgery or while sedated on a ventilator—their body continues to lose water. Water is lost through urine, feces, and "insensible" losses like evaporation from the skin and vapor in exhaled breath. If these fluids are not replaced, the patient will slowly become dehydrated.
The Holliday-Segar Method (4-2-1 Rule)
In 1957, Dr. Malcolm Holliday and Dr. William Segar published a paper linking fluid requirements to metabolic rate, which scales non-linearly with weight. Their derived formula is beautifully simple:
- For the first 10 kg of body weight: Give 4 mL/kg/hr.
- For the next 10 kg of body weight (11-20 kg): Give 2 mL/kg/hr.
- For every kilogram above 20 kg: Give 1 mL/kg/hr.
4 mL/kg/hr for the first 10 kg, PLUS 2 mL/kg/hr for the next 10 kg, PLUS 1 mL/kg/hr for every kg over 20 kg.
Example Calculation
Consider a 25 kg child:
- First 10 kg = 40 mL/hr
- Next 10 kg = 20 mL/hr
- Remaining 5 kg = 5 mL/hr
- Total: 65 mL/hr
This rule remains a cornerstone of pediatric and adult hospital medicine.