IV, infusion

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CHAPTER 16

IV Flow Rate Calculation

Objectives The learner will:

1. identify the calibrations in gtt/mL on IV administration sets.

2. calculate flow rates using dimensional analysis.

3. calculate flow rates using the formula and division factor methods.

4. recalculate flow rates to correct off-schedule infusions.

Suggested Review Questions 1. What information is needed to calculate the infusion rate of IV fluids in drops/minute?

2. What is the correct format for writing the equation when using dimensional analysis to

calculate IV flow rates?

3. What is a formula that can be used to calculate IV flow rates?

4. Explain the division factor method for calculating IV flow rates.

5. Explain the purpose and formula for recalculating the rate of IV fluids infusing via gravity

when they become off-schedule.

Answers to Review Questions 1. Infusion rates in drops/minute (gtt/min) are usually calculated when fluids are infusing by

gravity. The essential information needed to calculate the gtt/min rate is

a. the tubing drop factor, the number of gtt/mL

b. the prescribed infusion rate in mL/hr

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2. The format for constructing the DA equation to calculate IV flow rates in gtt/min is

tubing drop factor (gtt) amount of fluid to be infused (mL) 1 hrgtt/min = 1 mL time (in hr) min

× ×

Therefore, if 75 mL of IV fluid were to infuse each hour and the drop factor is 15 gtt/mL,

the equation would be

gtt 15 = min

1

gtt 1 mL

75 mL × 1 hr

1 hr × 60

4

= 18.75 = 19 gtt/min min

The DA equation can be simplified by substituting 60 minutes for the 1 hr entry. Thus, the

equation would be

tubing drop factor (gtt) amount of fluid to be infused (mL)gtt/min = 1 mL time in minutes

×

And if 75 mL of IV fluid were to infuse each hour and the drop factor is 15 gtt/mL, the

equation would be

gtt 15 = min

1

gtt 1 mL

75 mL × 60

4

= 18.75 = 19 gtt/min min

3. A formula that can be used to calculate IV flow rates (or drops per minute) is

gtt volume set calibration = min time in minutes

×

This formula is especially useful when the time for the infusion is 60 minutes or less.

4. To calculate IV infusion rates when the order is expressed in mL/hr and gtt/min the

division factor method can also be used. The division factor method is obtained by

dividing 60 by the drop factor of the IV administration set. Once the division factor is

known, it can be used to calculate the gtt/min by simply dividing the mL/hr ordered by the

division factor. For example, the division factor for IV tubing with a drop factor of 15 is 4

(60/15 = 4); if IV fluids are ordered at 75 mL/hr, the gtt/min are determined by dividing 75

by 4 = 18.75 or 19 gtt/min. Once the division factor has been determined for each of the

commonly used IV administration sets, it is remembered and used to quickly calculate the

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gtt/min for IV fluids ordered as mL/hr. The division factor for each of the commonly used

IV administration sets is

10 gtt/mL – division factor is 6

15 gtt/mL – division factor is 4

20 gtt/mL – division factor is 3

60 gtt/mL – division factor is 1

5. The rate of all continuous IV infusions should be counted by the nurse at least once each

hour, as changes in the fluid gravity pressure and position of the extremity where the IV

catheter is placed can alter the established IV infusion rate. The nurse needs to monitor the

IV so that the fluid does not infuse too quickly or too slowly. When assessing an IV

infusion that has become off-schedule, the remaining volume of fluid and time of infusion

are determined. IV rates that are found to be too fast are slowed down. IV rates that are too

slow are recalculated to the original ordered rate. Sometimes, the IV rate may be increased

so that the infusion can be completed within the ordered time frame; however, careful

assessment of the patient and consideration of the type of fluid infusing (i.e., does it

contain a medication) is done to determine if increasing the infusion rate above the ordered

rate has the potential to harm the patient. Always follow the hospital policy related to

increasing infusion rates.

The formula for recalculating IV infusion rates is the same for increasing and

decreasing the IV rate. The remaining infusion time and volume are used to determine the

number of mL/hour that should infuse to complete the infusion within the ordered time

frame. The mL/hour is then divided by the division factor to determine the adjusted

infusion rate. The two step formula is

(1) Volume remaining ÷ time remaining = mL/hr to infuse

(2) mL/hr to infuse ÷ division factor = gtt/min

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Name ____________________________________________ Date ____________________

Chapter 16: IV Flow Rate Calculation

Additional Practice Problems Calculate the IV flow rate in gtt/min for the following IV solutions and medications. Round answers to the nearest whole number (or drop).

1. An IV piggyback of piperacillin diluted in 50 mL of 0.9% NaCl is to infuse in 20 minutes.

The set calibration is 20 gtt/mL.

___________

2. 1000 mL of lactated Ringer’s is to infuse over 12 hr. The set calibration is 15 gtt/mL.

___________

3. An IV piggyback of gentamicin diluted in 100 mL of 5% dextrose in water is to infuse in

1 hr. The set calibration is 10 gtt/mL.

___________

4. Your patient is to receive 1000 mL of D5 0.45% NaCl over 24 hr. The set calibration is

60 gtt/mL.

___________

5. Your patient is to receive 1500 mL of 0.9% NaCl over 10 hours. The set calibration is

10 gtt/mL.

___________

6. An IV piggyback of 500 mg imipenem-cilastatin sodium diluted in 50 mL D5W is to

infuse over 30 minutes. The set calibration is 15 gtt/mL.

___________

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7. 10 mL of IV medication are to infuse in 15 minutes. A microdrip infusion set is used.

___________

8. An IV piggyback of 200 mg ciprofloxacin hydrochloride diluted in 100 mL of 0.9% NaCl

is to infuse over 45 minutes. The set calibration is 20 gtt/mL.

___________

9. An order for 125 mL of D5 0.9% NaCl per hour is written. The set calibration is

15 gtt/mL.

___________

10. A child is to receive 500 mL of D5W over the next 12 hours. A microdrip infusion set is

used.

___________

Recalculate the flow for the infusions below to complete on schedule. Calculate the gtt/min and round answers to the nearest whole number (or drop).

11. An IV of 1000 mL was scheduled to infuse in 8 hours. After 3 hours, you note that 600 mL

have infused. The set calibration is 10 gtt/mL.

___________

12. An IV of 500 mL was started at 8:00 AM to infuse over 5 hours. At 10:00 AM you note

that 125 mL have infused. The set calibration is 15 gtt/mL.

___________

13. An IV of 1000 mL was infusing at 100 mL/hr. After 300 mL had infused, the order was

written to complete the infusion within the next 4 hours. Set calibration is 20 gtt/mL.

___________

14. A 250 mL bag of IV fluid was to infuse in 2 hours. After 1 hour you note that 150 mL

have infused. Set calibration is 10 gtt/mL.

___________

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15. A volume of 400 mL of fluid was to infuse over 5 hours. After 2 hours you note that

200 mL already infused. Set calibration is 15 gtt/mL.

___________

16. 125 mL of IV fluid are to infuse over 3 hours. After 1 hour you note that only 25 mL have

infused. Set calibration is 60 gtt/mL.

___________

17. An IV of 1000 mL is ordered to infuse over 6 hours. After 3 hours, you note that 750 mL

have already infused. Set calibration is 20 gtt/mL.

___________

18. 750 mL of IV fluid are to infuse over 3 hours. After 1 hr and 30 minutes you note that

400 mL have infused. Set calibration is 10 gtt/mL.

___________

19. An IV of 250 mL of solution is infusing at 25 mL/hour. After 3 hours you note that

125 mL of solution have infused. Set calibration is 60 gtt/mL.

___________

20. 800 mL has inused from a 1000 mL IV bag in 5 hours. The drip rate had been set so that

the infusion would be complete in 10 hours. Set calibration is 15 gtt/mL.

___________

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Solutions to Additional Practice Problems Calculate the IV flow rate in gtt/min for the following IV solutions and medications. Round answers to the nearest whole number (or drop).

1. Since the infusion time is less than 60 minutes, the formula method is used.

Answer = 50 gtt/min.

50 mLgtt/min = 20× 1

gtt/ mL 20

1

= 50 gtt/min min

2. The infusion time is greater than 1 hr, so dimensional analysis is used.

Answer = 21 gtt/min.

gtt 15 = min

1

gtt 1 mL

1000 mL × 12 hr

1 hr × 60

4

1000= = 20.8 = 21 gtt/min 48 min

3. The infusion time is 1 hr. Either the formula or dimensional analysis method can be used.

Answer = 17 gtt/min.

Formula method:

100 mLgtt/min = 10× 1

gtt/ mL 60

6

100= = 16.6 = 17 gtt/min 6min

Dimensional analysis:

gtt 10 = min

1

gtt 1 mL

100 mL × 1 hr

1 hr × 60

6

100= = 16.6 = 17 gtt/min 6 min

4. The infusion time is greater than 1 hr, so dimensional analysis is used.

Answer = 42 gtt/min.

gtt 60 = min

1

gtt 1 mL

1000 mL × 24 hr

1 hr × 60

1

1000= = 41.6 = 42 gtt/min 24 min

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5. The infusion time is greater than 1 hr, so dimensional analysis is used.

Answer = 25 gtt/min.

gtt 10 = min

1

gtt 1 mL

1500 mL × 10

1 hr

1 hr × 1500= = 25 gtt/min 60 min 60

6. Since the infusion time is less than 60 minutes, the formula method is used.

Answer = 25 gtt/min.

50 mLgtt/min = 15× 1

gtt/ mL 30

2

50= = 25 gtt/min 2min

7. Since the infusion time is less than 60 minutes, the formula method is used.

Answer = 40 gtt/min.

10 mLgtt/min = 60× 4

gtt/ mL 15

1

= 40 gtt/min min

8. Since the infusion time is less than 60 minutes, the formula method is used.

Answer = 44 gtt/min.

100 mLgtt/min = 20 gtt/ mL× 2000= = 44.4 = 44 gtt/min 45 min 45

9. The infusion time is 1 hr. Either the formula or dimensional analysis method can be used.

Answer = 31 gtt/min.

Formula method:

125 mLgtt/min = 15× 1

gtt/ mL 60

4

125= = 31.2 = 31 gtt/min 4min

Dimensional analysis:

gtt 15 = min

1

gtt 1 mL

125 mL × 1 hr

1 hr × 60

4

125= = 31.2 = 31 gtt/min 4 min

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10. The infusion time is greater than 1 hr, so dimensional analysis is used.

Answer = 42 gtt/min.

gtt 60 = min

1

gtt 1 mL

500 mL × 12 hr

1 hr × 60

1

500= = 41.6 = 42 gtt/min 12 min

Recalculate the flow for the infusions below to complete on schedule. Calculate the gtt/min and round answers to the nearest whole number (or drop). [Note: recalculation is computed based on mL/hr; therefore, the formula method has been used in the calculations below.]

11. Time remaining: 8 hr – 3 hr = 5 hr

Volume remaining: 1000 mL − 600 mL = 400 mL

400 mL 5 hr = 80 mL/hr

80 mL

÷

10× 1

gtt/ mL 60

6

80 = = 13.3 = 6min

13 gtt/min

12. Time remaining: 5 hr − 2 hr = 3 hr

Volume remaining: 500 mL − 125 mL = 375 mL

375 mL 3 hr = 125 mL/hr

125 mL

÷

15× 1

gtt/ mL 60

4

125 = = 31.2 = 4min

31 gtt/min

13. Time remaining: 4 hr

Volume remaining: 1000 mL − 300 mL = 700 mL

700 mL 4 hr = 175 mL/hr

175 mL

÷

20× 1

gtt/ mL 60

3

175 = = 58.3 = 3min

58 gtt/min

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14. Time remaining: 2 hr − 1 hr = 1 hr

Volume remaining: 250 mL − 150 mL = 100 mL

100 mL 1 hr = 100 mL/hr

100 mL

÷

10× 1

gtt/ mL 60

6

100 = = 16.6 = 6min

17 gtt/min

15. Time remaining: 5 hr − 2 hr = 3 hr

Volume remaining: 400 mL − 200 mL = 200 mL

200 mL 3 hr = 66.6 mL/hr

66.6 mL

÷

15× 1

gtt/ mL 60

4

66.6 = = 16.6 = 4min

17 gtt/min

16. Time remaining: 3 hr − 1 hr = 2 hr

Volume remaining: 125 mL − 25 mL = 100 mL

100 mL 2 hr = 50 mL/hr

50 mL

÷

60× 1

gtt/ mL 60

1

= min

50 gtt/min

17. Time remaining: 6 hr − 3 hr = 3 hr

Volume remaining: 1000 mL − 750 mL = 250 mL

250 mL 3 hr = 83.3 mL/hr

83.3 mL

÷ 1

20 gtt/ mL× 60

3

83.3 = = 27.7 = 3min

28 gtt/min

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18. Time remaining: 3 hr − 1.5 hr = 1.5 hr

Volume remaining: 750 mL − 400 mL = 350 mL

350 mL 1.5 hr = 233.3 mL/hr

233.3 mL

÷

10× 1

gtt/ mL 60

6

233.3 = = 38.8 = 6min

39 gtt/min

19. If 250 mL are infusing at 25 mL/hr, the entire infusion would take 10 hr.

Time remaining: 10 hr − 3 hr = 7 hr

Volume remaining: 250 mL − 125 mL = 125 mL

125 mL 7 hr = 17.85 (rounded to nearest 10th) = 17.9 mL/hr

17.9 mL

÷ 1

60 gtt/ mL× 60

1

= 17.9 = min

18 gtt/min

20. Time remaining: 10 hr − 5 hr = 5 hr

Volume remaining: 1000 mL − 800 mL = 200 mL

200 mL 5 hr = 40 mL/hr

40 mL

÷

15× 1

gtt/ mL 60

4

40 = = 4min

10 gtt/min