This rule helps to easily calculate the maintenance fluid needs in hospitalized patients.

Maintenance fluid can be defined as the amount of fluid required to compensate for ongoing fluid losses (insensible and sensible), thus maintaining steady state in the body.

In a study published in 1957 in the Journal of Paediatrics, Malcolm Holiday and William Segar developed a simple rule that can be easily remembered for calculating maintenance fluid in sick children.

This rule is based on the assumption that there exists a DIRECT LINEAR RELATIONSHIP between physiologic water and energy metabolism (that is, under normal resting conditions, 1ml of body water is required to metabolize 1KCal).

These authors (Holliday and Segar), having also understood that there is a relationship (NON-LINEAR) between body weight and energy expenditure, therefore plotted a graph showing this relationship. By this, they arrived at a method that can help to calculate maintenance fluid using body weight, based on the the established DIRECT LINEAR relationship between body water and energy metabolism.

And here is the conclusion:

First 10kg (0-10kg) will require 100ml/kg/day

Second 10kg (11-20kg) will require 50ml/kg/day

Remaing kg (>20kg) will require 20ml/kg/day

This formula is then simplified to produce the 4-2-1 rule, by expressing the maintenance fluid in “per hour” instead of “per day”.

To achieve this, the amount of fluid is divided by 24 (since 1day= 24hours).

0-10 kg= 100ml/kg ÷ 24= 4.167 (approx. 4ml/kg/hr)

11-20kg = 50ml/kg ÷ 24= 2.083 (approx. 2ml/kg/hr)

>20kg= 20ml/kg ÷ 24= 0.83 (approx. 1ml/kg/hr)

And that’s the 4-2-1 rule for calculating HOURLY MAINTENANCE FLUID.

**Example 1:**

What is the daily maintenance fluid for a sick child weighing 12kg? Also, calculate the maintenace fluid to be administered to this child over a period of 8hrs.

Weight of the child is 12kg (10kg + 2kg)

First 10kg= 100ml/kg/day= 100ml*10= 1000ml/day

Second 2kg= 50ml/kg/day= 50ml*2= 100ml/dayThe daily maintenance fluid for the child

= 1000ml + 100ml= 1100ml/day.To calculate the 8hrs period maintenance fluid, convert daily maintenance to hourly maintenance, and multiply the result by 8.

1100ml ÷ 24= 45.83ml/hr

Maintenance fluid for a period of 8hrs

= 45.83ml*8

= 366.64 (approx. 367ml).

**Example 2:**

Using the 4-2-1 rule, calculate the hourly maintenance fluid for a sick child weighing 25kg.

Weight= 25kg (10kg + 10kg + 5kg)

First 10kg= 4ml*10= 40ml/hr

Second 10kg= 2ml*10= 20ml/hr

Last 5kg= 1ml*5= 5ml/hrThe hourly maintenance fluid

= 40+20+5

= 65ml/hr.To calculate the daily maintenance fluid, simply multiply by 24hrs

Daily maintenance fluid for this child= 65ml*24= 1560ml per day.

*OGUNLABI, David (RN).*