For more information about this and other math topics, come to the Math Lab 722-6300 x 6232. Caproiu & Hall, 2000
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Math for Nursing
Flow Rate Calculation
Many intravenous fluids are frequently ordered on the basis of mL/hr.
The size of the drops is regulated by the size of the IV tubing. IV tubings are
calibrated in gtt/ mL and this calibration is needed to calculate the flow rate.
The type of tubing is usually 10, 15, or 20 gtt to equal 1 mL in standard
microdrip sets, and 60 gtt to equal 1 mL in mini or microdrip sets. The
calibration, in gtt/ mL is clearly printed on each IV package.
To calculate the numnber of drops per minute the nurse needs to know the
prescribed medication over the prescribed infusion time, and the drop factor
of the device.
Example:
One liter of Normal Saline is charted over 9 hours. The drop factor is 15.
Calculate the number of drops per minute.
What is given?
What is asked:
Number of drops to be infused per minute
Use conversion factors 1,000 mL = 1 L 1h = 60 minutes
Start in the numerator with the units you are looking for and use dimensional
analysis.
Cross cancel same units and multiply the numerators and the denominators.
The result will be:
×× ×
15 gtt 1 L 1 hr 1,000 mL
1 mL 9 hr 60 min 1 L
- The infusion amount 1 L of NS
- Microdrip IV set calibration
- Infusion time 9 hours
15 gtt
1mL
28 drops
min
Because drops need to be a whole number the answer will be
=27.77
Cross cancel zeros and divide
15,000
540
