Sample 1 of 2
500 mL via micro-drip set (60 drops/mL) over 6 hours. Drip rate in drops/min, to the nearest whole number?
Give your answer in drops/min.
Answer:83
Why
(500 x 60) / (6 x 60) = 30000/360 = 83.33, rounds to 83.
NMC Standards
Intravenous infusion rates
Written and checked against the NMC’s published sources by The NMCMATE editorial team.Last checked .
3 marks of the 15 in Part A, which runs for 30 minutes.
Two kinds of question live here. A pump wants millilitres an hour, which is a division. A gravity set wants drops a minute, which needs the drop factor of the set and a conversion from hours to minutes. Knowing which one you have been asked is half the mark.
What this section asks about
- Pump rates: total volume divided by the hours it runs over
- Drip rates: volume times the drop factor, divided by the time in minutes
- Drop factors, which differ between a standard set, a blood set and a micro-drip set
- Recalculating a rate partway through, when an infusion is behind or ahead
- Continuous infusions prescribed in units or micrograms per hour
Where the marks go
3 marks of the 15 in Part A, which runs for 30 minutes.
Every numeracy question sits at the apply and analyse level: you are given a situation and asked to work something out, rather than to recall a fact.
Worked examples
The method, with the answer shown. Practise below once you have the shape of it.
1,000 mL of sodium chloride 0.9% over 8 hours on a pump. What rate?
- Total volume divided by the time in hours.
- 1,000 / 8
Answer: 125 mL per hour
If the prescription gives the time in minutes, convert to hours first. 500 mL over 30 minutes is 500 / 0.5, which is 1,000 mL per hour, not 500.
500 mL over 4 hours through a standard giving set of 20 drops per mL. What drip rate?
- Volume times the drop factor, divided by the time in minutes.
- 4 hours is 240 minutes.
- 500 x 20 / 240 = 41.67
Answer: 42 drops per minute
Check the set before you start. Calculating at 20 drops per mL when the set is a 60 drop micro-burette gives an answer three times too low.
1,000 mL was prescribed over 10 hours. Four hours in, only 300 mL has gone through. What rate now?
- Work with what is left, not what was prescribed.
- 700 mL remaining over the 6 hours remaining.
- 700 / 6 = 116.67
Answer: 117 mL per hour
Recalculating from the original volume and the original time gives 125 mL per hour and leaves the patient behind for the rest of the infusion.
Where candidates lose marks
- Using hours where the formula wants minutes. Multiply by 60 before you divide.
- Assuming a drop factor. The question states it, and 20, 15 and 60 drops per millilitre give three different answers.
- Leaving a drip rate as a decimal. You cannot set half a drop, so round to the nearest whole drop.
Sample questions
From our bank, with the explanation as a student sees it. These particular questions are kept out of the mock papers, so reading them here does not use anything up.
Sample 2 of 2
A patient needs 0.9% NaCl 1500 mL over 12 hours. Rate in mL/hour?
Give your answer in mL/hour.
Answer:125
Why
1500 / 12 = 125 mL/hour.
NMC Standards
Questions people ask
- Do I have to remember the drop factors?
- No. The question tells you the set it wants you to use. What you have to remember is that the factor belongs in the calculation.
- Are infusion questions in Part A or Part B?
- The calculation is in Part A, with the calculator. Part B may ask about the same infusion in clinical terms, such as what to check before it starts.
Practise this section
Practice is filtered by section, so you can work on this one on its own. Every account gets 10 new questions a day without a card.
This is one of the fifteen sections the paper is built from. Work through the whole thing with the NMC CBT study guide.