# IV FLUID MAINTENANCE RATE CALCULATION

Calculating intravenous venous fluid maintenance rate can be important part of the anesthetic management of adult and pediatric patient undergoing surgical procedure.

It is crucial component of pediatric anesthesia for any surgical procedure.

Intravenous fluid maintenance is generally calculated as an hourly rate for anesthesia purpose.

To accommodate patient ranging in size premature neonates to adults, a formula bases on the patients weight in kilograms is typically used that follows the form 4:2:1

4mL/kg/hr for the first 10 kilograms of the body weight

+

2mL//kg/hr for the next 10 kilogram of the body weight

+

1mL/kg/hr for the each kilogram thereafter

This formula is not typically intuitive at first so we will use the few examples to demonstrate it

## What is the IV fluid maintenance rate of 5kg infant ?

According to the formula 4:2:1, it says that we should use 4mL/hr for the first 10 kg but this patient is only of 5 kg

so we simply multiply 4mL/hr * 5kg = 20mL/hr

so a 5 kg patient would have the IV fluid maintenance rate of 20mL/hr

### What is the IV fluid maintenance rate of 19 kg patient ?

Looking at the formula we should multiply 4mL/hr for the 1st 10 kg and 2mL/hr for the next 10 kg , since our patient is 19 kg the formula should be applied as ,

19 kg= 10 kg + 9 kg

so for the 1st 10 kg –> 4mL/hr * 10 kg = 40mL/hr

for the next 9 kg –> 2mL/hr * 9 kg = 18 mL/hr

so a 19 kg patient would have IV fluid maintenance rate of40mL/hr +18 mL/hr = 58mL/hr

Now lets try another example for the 55 kg patient

#### What is the IV fluid maintenance rate of 55 kg patient ?

Looking at the formula we should multiply 4mL/hr for the 1st 10 kg and 2mL/hr for the next 10 kg , and 1mL/hr for the rest. since our patient is 55 kg the formula should be applied as

55 kg= 10 kg + 10 kg + 35 kg

so for the 1st 10 kg –> 4mL/hr * 10 kg = 40mL/hr

for the next 10 kg –> 2mL/hr * 10 kg = 20 mL/hr

for the rest 35 kg –> 1mL/hr * 35 kg = 35 mL/hr

Now we will add 40mL/hr + 20 mL/hr + 35 mL/hr = 95 mL/hr

so a 55 kg patient would have the IV fluid maintenance rate of 95mL/hr

##### What is the relationship between the patients weight and the their fluid maintenance rate ?

The weight of patient is 55 kg &

the fluid maintenance rate is 95mL/hr

so the maintenance rate exactly 40% higher than the weight in kilograms

Note: so if the patient’s weight is more than 20 kg , we can just add 40 in the weight of the patient just to calculate hourly IV fluid maintenance rate .

Now lets find a shortcut formula to calculate IV fluid maintenance rate

Patients who weigh at least 20 kg have an hourly maintenance rate that is their weight in kilograms plus 40

Formula

20 kg patient = Weight of patient + 40

Now lets try this formula for the 30 kg patient

###### What is the IV fluid maintenance rate of 30 kg patient ?

Here the patient’s weight is more than 20 kg , so we can apply simplified shortcut formula just by adding 40 in the weight of the patient.

IV fluid maintenance rate of 30 kg patient = 30 kg + 40 = 70mL/hr

According to this shortcut formula

IV fluid maintenance rate of 90 kg patient = 90 kg + 40 = 130mL/hr

IV fluid maintenance rate of 110 kg patient = 110 kg + 40 = 150mL/hr

IV fluid maintenance rate of 45 kg patient = 45 kg + 40 = 85mL/hr

IV fluid maintenance rate of 65 kg patient = 65 kg + 40 = 105mL/hr

NOTE: This formula applies only for the patients who weigh at least 20 kg.This formula is not applicable for the patient who weigh less than 20 kg , for less than 20 kg we must apply 4:2:1 formula

For some problems you may need to convert weight into kilograms.

NOW LETS CALCULATE THE DROPS PER MINUTE

In a normal adult IV set , 1 mL= 16 drops (Approx)

In a normal pediatric IV set , 1 mL= 64 drops (Approx)

Now we use the formula rule of 4

Drop rate = Number of drops per minute

Drop rate   = {Maintenance rate (Volume in mL/hr)} / 4

Now lets demonstrate this formula with an example by calculating drops per minute of a 90 kg patient with the fluid maintenance rate of 130mL/hr

(Fluid maintenance rate is calculated here by using the shortcut formula of adding 40 in the patients weight )

EXAMPLE 1

If 130mL fluid is to infused in 1hr

Drop rate   = {Maintenance rate (Volume in mL/hr)} / 4

= 130mL/4

= 32.5 drops/min approx

Now lets verify this

130mL in 1 hour(60min) = 130/60 = 2.16mL/min

so in 1 min 2.16mL should be infused

In an adult IV set each ml contains 16 drops

so 2.16mL in 1 min = 2.16mL*16 drops = 34.56 drops/min

Conclusion: 34.56 drops per minute fluid should be infused for the maintenance rate of 130mL/hr

Drop rate   = Volume in mL per day / 100

= 3000mL/100

= 30 drops/min (approx)EXAMPLE 2

If 200mL fluid is to infused in 1hr

Drop rate   = {Maintenance rate (Volume in mL/hr)} / 4

= 200mL/4

= 50 drops/min approx

Now lets verify this

200mL in 1 hour(60min) = 200/60 = 3.33mL/min

so in 1 min 3.33mL should be infused

In an adult IV set each ml contains 16 drops

so 3.33mL in 1 min = 3.33mL*16 drops = 53.28 drops/min

Conclusion: 53.28 drops per minute fluid should be infused for the maintenance rate of 200mL/hr

NOW IF THE VOLUME OF FLUID TO BE INFUSED FOR A DAY IS GIVEN

Then, Drop rate = Volume in mL per day / 100

Drops per min  = Volume in (mL per day ) / 100

Now lets demonstrate this formula with an example

3000 mL fluid to be infused in a day (24hr)

If 3000mL fluid is to infused in a day (24hr)

Now lets verify this

3000mL in a day 24 hour = 30000/24 = 125 mL/min

125mL per hour (60 min) = 125/60 = 2.08 mL/min

so in 1 min 2.08mL fluid should be infused

In an adult IV set each ml contains 16 drops

so 2.08 mL in 1 min = 2.08mL*16 drops = 33.28 drops/min

Conclusion: 33.28 drops per minute fluid should be infused for the maintenance rate of 3000mL/day in 24 hr

QUICK REVIEW FORMULAS

1) IV fluid maintenance rate = 4:2:1 (for more or less than 20 kg patients)

4mL/kg/hr for the first 10 kilograms of the body weight

+

2mL//kg/hr for the next 10 kilogram of the body weight

+

1mL/kg/hr for the each kilogram thereafter

2) Shortcut formula for more than 20 kg patients: IV fluid maintenance rate = weight of patient in kg  + 40

3) Drop rate   = {Maintenance rate (Volume in mL/hr)} / 4

4) Drop rate calculation for a day  = Volume in mL per day / 100