# 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 of**40mL/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** **–> 1**mL/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*

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