What is the 4-2-1 rule (four-two-one rule) for estimating maintenance fluid requirements in pediatric patients?

From the Guidelines

The 4-2-1 rule is a widely accepted method for estimating maintenance fluid requirements in pediatric patients, where children need 4 mL/kg/hour for the first 10 kg of body weight, 2 mL/kg/hour for the next 10 kg, and 1 mL/kg/hour for each kilogram above 20 kg. This rule is based on the physiological principle that metabolic rate and fluid requirements per kilogram decrease as body weight increases 1. For example, a 25 kg child would require 40 mL/hour for the first 10 kg, plus 20 mL/hour for the next 10 kg, plus 5 mL/hour for the remaining 5 kg, totaling 65 mL/hour or 1,560 mL/day.

Key Considerations

• The calculated maintenance fluids typically consist of isotonic solutions (like 0.9% normal saline or Lactated Ringer's) with appropriate dextrose concentration based on age 1.
• It's essential to adjust this baseline calculation for factors like fever (increase by 10-15% per degree Celsius above normal), increased insensible losses, or clinical conditions affecting fluid balance.
• Regular reassessment of the patient's fluid status through vital signs, urine output, and electrolyte levels is crucial for appropriate management 1.

Clinical Application

• The 4-2-1 rule provides a practical and straightforward method for estimating maintenance fluid requirements in pediatric patients.
• However, it's crucial to consider individual patient factors and adjust the calculation accordingly to avoid complications such as fluid overload or hyponatremia 1.
• The use of isotonic fluids and balanced solutions is recommended to reduce the risk of hyponatremia and other complications 1.

Evidence-Based Recommendations

• The ESPNIC clinical practice guidelines recommend using isotonic fluids and balanced solutions for intravenous maintenance fluid therapy in acutely and critically ill children 1.
• The guidelines also emphasize the importance of regular reassessment of the patient's fluid status and adjusting the fluid therapy accordingly 1.

From the Research

Overview of the 4-2-1 Rule

• The 4-2-1 rule, also known as the four-two-one rule, is a traditional method for estimating maintenance fluid requirements in pediatric patients 2.
• This rule suggests that for every 100 mL of fluid administered, 4 mL should be given for the first 10 kg of body weight, 2 mL for the next 10 kg, and 1 mL for each kilogram above 20 kg 2.

Limitations and Controversies

• The traditional recommendations for maintenance fluids, including the 4-2-1 rule, have been increasingly criticized for not consistently applying in acute illness, where energy expenditure and electrolyte requirements deviate significantly from the original estimates 3.
• Studies have shown that using hypotonic intravenous fluids, as suggested by the 4-2-1 rule, may lead to an increased incidence of hyponatremia in pediatric patients 4, 5.
• The use of isotonic fluids as maintenance therapy has been suggested as a way to prevent iatrogenic hyponatremia in pediatrics 5.

Current Practices and Recommendations

• A survey of pediatric hospitalists found that isotonic solutions were preferred in older children, while hypotonic fluids were more commonly chosen in the neonatal period 6.
• The American Academy of Pediatrics Clinical Practice Guideline recommends the use of isotonic fluids as maintenance therapy in pediatric patients outside of the neonatal period 6.
• Studies have shown that the use of isotonic fluids does not increase the incidence of adverse events compared to hypotonic fluids 5.