Maintenance IV Fluids (4-2-1 Rule)

Why use it

Universal standard for maintenance fluid calculation. Essential for pediatric fluid management. Used perioperatively, in NPO patients, and as a starting point for IV fluid orders.

About

The Holliday-Segar method (4-2-1 rule) calculates maintenance fluid requirements based on body weight. It is the standard method for determining baseline IV fluid rates in both pediatric and adult patients. The rule provides hourly and daily rates that approximate insensible losses and basal metabolic water requirements.

When to use

• Any patient requiring maintenance IV fluids
• Perioperative fluid management
• NPO patients needing basal hydration
• Pediatric fluid calculations

Formula

Pearls & pitfalls

• 4 mL/kg/h for first 10 kg, 2 mL/kg/h for next 10 kg, 1 mL/kg/h for each kg above 20.
• Daily equivalent: 100 mL/kg for first 10 kg, 50 mL/kg for next 10 kg, 20 mL/kg per kg above 20.
• Maximum practical maintenance rate is typically ~125 mL/h for adults (rarely exceed this).
• This formula does NOT account for ongoing losses, fever, or pathological states.
• In pediatrics, electrolyte composition of maintenance fluids is critical — isotonic fluids (NS or balanced) preferred to reduce hyponatremia risk.
• The rule slightly overestimates needs in obese patients — consider ideal body weight.

Next steps

Maintenance rate is a STARTING point. Adjust for: fever (+10% per °C above 37°C), ongoing losses (drains, NG, diarrhea), third-spacing, renal function. Choose appropriate fluid (D5 0.45% NS for adults, D5 0.2% NS for young children — follow institutional protocols).

Evidence

Holliday and Segar (Pediatrics, 1957). Based on metabolic rate and water requirements. Universally adopted worldwide. Recent NICE and AAP guidelines recommend isotonic maintenance fluids in children to prevent hospital-acquired hyponatremia.

References

1. Holliday MA, Segar WE. The maintenance need for water in parenteral fluid therapy. Pediatrics. 1957;19(5):823-832. — link