Calculating Flow Rates

• Flow rate– Calculated from

• amount of fluid to be infused

• length of time for infusion

– Expressed as milliliters per hour

Calculating Flow Rates (cont.)

Rule 15-5 Rule 15-5 To calculate flow rates in milliliters per hour, identify the following:

V (volume)T (time)F (flow rate)

Formula:

Calculating Flow Rates (cont.)

Find the flow rate using the formula method

Ordered: 500 mg ampicillin in 100 mL NS, infuse over 30 minutes

Convert minutes to hour: 30 ÷ 60 = 0.5 hr

Flow rate = 200 mL/hr

ExampleExample

Calculating Flow Rates (cont.)

Find the flow rate using Dimensional Analysis.

Ordered: 500 mg ampicillin in 100 mL NS to infuse over 30 minutes

F mL/h = 100 mL / 30 min x 60 min /1 h

F mL/h = 600 mL / 30 h

Flow rate = 200 mL/hr

ExampleExample

Calculating Flow Rates (cont.)

• Manually regulated IVs– Calculated as gtt/min

– Macrodrip tubing• Larger drops• Drop factors: 10 gtt/mL,

15 gtt/mL, or 20 gtt/mL

– Microdrip tubing • Smaller drops• Drop factor: 60 gtt/mL

Calculating Flow Rates (cont.)

Rule 15-6 Rule 15-6 To determine flow rate (f) in drops per minute:1. Change the flow rate mL/h (F) to gtt/min (f) using

the formula:

C = calibration factor of tubing60 = minutes/hour

Calculating Flow Rates (cont.)

Find the flow rate in drops perminute that is equal to 35 mL/hour using 60 gtt/mL microdrop tubing.

Formula method:

f = 35 gtt/min

ExampleExample

Calculating Flow Rates (cont.)

Find the flow rate in drops perminute that is equal to 35 mL/hour using 60 gtt/mL microdrop tubing.

Dimensional analysis:

f gtt/min = 35 mL / 1 h x 1 hr / 60 min x 60 gtt / 1mL

f gtt/min = 35 x 60 gtt / 60 min

f = 35 gtt/min

ExampleExample

Adjusting Flow Rates

• Counting drops– Check IV hourly to see if

it is on schedule.

– Before adjusting the rate, check facility policy.

Adjusting Flow Rates (cont.)

Rule 15–7Rule 15–7 To adjust the flow rate:

Recalculate the infusion, using the volume remaining in the IV and the time remaining in the order.

Check the guidelines at your facility before adjusting the flow rate.

Adjusting Flow Rates (cont.)

Original Order: 1500 mL NS over 12 hours

The IV was infusing at an original rate of 42 gtt/min using 20 gtt/mL macrodrip tubing.

After 3 hours, 1200 mL remain in the bag.

ExampleExample

Adjusting Flow Rates (cont.)

Use formula

f = 44gtt/min = adjusted flow rate

Example (cont.)Example (cont.)

Practice

Calculate flow rate; then determine if an adjustment is necessary.

Ordered: 250 mL NS over 2 hours (10 gtt/mL tubing)

After 30 minutes 100 mL infused.

ANSWER: Original flow rate = 21 gtt/min

Adjusted flow rate = 17 gtt/min