Duration of an Infusion (How long an infusion to finish)

1. How long an infusion to finish ?

In the NMC CBT numeracy exam, you may be asked to calculate how long an intravenous (IV) infusion will take to finish. This calculation is important for ensuring that IV fluids are administered safely at the prescribed rate. To calculate the infusion time, you need to know the total volume of fluid in mL and the infusion rate in mL/hour. 

The basic formula is: Time = Volume ÷ Rate

Example 1,

A patient is prescribed 1,000 mL of sodium chloride 0.9%.
The infusion pump is running at 125 mL/hour.

Calculation:

1,000 ÷ 125 = 8 hours

Answer: 8 hours

Example 2,

An infusion contains 500 mL and is running at 100 mL/hour.

500 ÷ 100 = 5 hours

Answer: 5 hours

CBT Tip: If the question asks “How long will the infusion take to finish?”, remember:

Volume ÷ Rate = Time