IV Infusion Set Calculations

It is imperative to understand how to calculate IV Infusion/IV mixture, dosage, and rate of flow in preparing for the PTCB or ExCPT exams. This page is dedicated to IV administration sets that serve the mixture to the end user (Patient).

IV Infusion sets are pre-calibrated to how many drops per ml(gtt/ml) of a solution they administer to the patient.

This is
NOT to be confused with Drops per Minute (gtt/min). Drops per minute can be adjusted on the device. It is very important to never confuse the two.

Here is the basic formula:

Flow Rate Formula

Memorize the difference of the two.
Drop Factor gtt/mL IV Infusion devices are calibrated to deliver so many Drops per Milliliter.
gtt/min A nurse will set the device to dispense so many drops per minute in order to achieve the proper ml/min.

Let's use an example similar to the one on the
last page :

The patient is prescribed:

720ml of mixture over 6 hours

720mL ÷ 6 Hrs = 120mL/Hr

determine how much per Minute.

120mL/Hr ÷ 60(min/Hr) = 2mL/min

We arrived at

The Infusion set device delivers
10 gtt/ml,

Now, simply take the amount of
ml/min and multiply it by the gtt/ml.

2ml/min x 10gtt/ml = 20gtt/min

This example seemed very easy, right? Well, it really is just that easy. The only things that makes it more complicated are fractions, decimals and rounding up to the nearest drop. As long as you keep gtt/ml and gtt/min straight the rest is just math. Would you rather watch a video? Here's one -
Video Tutorial

Another flow rate calculation example

Question from Angel on Yahoo! Answers
A 110lb woman is started on a nitroglycerin IV drip.The order is to administer the nitroglycerin at 5mcg/min. The pharmacy sends a 250ml IV container with 25mg of nitroglycerin added to the container. What rate in ml/hr should the IV run?

The patients weight is irrelevant. The 250ml IV is just saline and used as a vehicle to carry the active drug into the patient's body. Angel is in pharmacy tech school and I know she knows some math. So....

First you need to convert your mg's to mcg's.

Next, using proportions math you can determine how many mL's are needed to deliver 5mcg's.

          Here is how it will look:





You now know that
0.05 ml contains 5mcg

The patient needs 5mcg/min, so they need 0.05 ml/min

0.05 ml    x     60 min    = 3ml/Hour

The Answer is 3ml/Hour

Flow rate calculations tutorial
By Zita Schmitt, CPhT


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IV Infusion flow rate example