CBT numeracy, set up right.
Part A has 15 calculation questions in 30 minutes, and the 2021 test specification puts the pass mark at 13 right. You type each answer as a number, sometimes with its unit, and an on-screen calculator is there. Most marks go in setting up the sum, not in the arithmetic. [S2] [S5] [S4]
The six topics
| Topic | In a real test | In our bank |
|---|---|---|
| Measuring the correct dose | 2 | 10 |
| Metric units | 2 | 10 |
| Oral medications | 4 | 20 |
| Injections | 3 | 15 |
| Intravenous infusions | 3 | 15 |
| Fluid balance | 1 | 5 |
Four set-ups that cover most questions
Volume = dose wanted ÷ stock strength × stock volume
Pump rate (mL/hour) = volume ÷ hours
Drops per minute = volume (mL) × drops per mL ÷ minutes
Fluid balance = total intake − total output
Two worked examples
Mr Clarke cannot swallow tablets and is prescribed 750 mg of paracetamol. The ward stocks paracetamol oral suspension 250 mg in 5 mL. What volume in mL should you measure?
- Dose wanted is 750 mg. Stock is 250 mg in 5 mL.
- Volume = dose wanted / strength x volume = 750 / 250 x 5.
- 750 / 250 = 3, and 3 x 5 = 15.
- Answer: 15 mL
Watch for: Stopping at 3 and forgetting to multiply by the 5 mL that holds each 250 mg.
A patient is prescribed 500 mL of intravenous fluid over 6 hours through a gravity giving set that delivers 20 drops per mL. How many drops per minute, to the nearest whole number?
- Total drops = 500 mL x 20 drops/mL = 10,000 drops.
- Minutes = 6 hours x 60 = 360 minutes.
- Drops per minute = 10,000 / 360 = 27.78.
- Round to the nearest whole number.
- Answer: 28 drops/minute
Watch for: Dividing by the 6 hours instead of the 360 minutes, which gives about 1,667 drops/minute.
Unit rules that cost marks
- Convert before you calculate: 1 g is 1,000 mg, 1 mg is 1,000 micrograms, 1 litre is 1,000 mL.
- Give the unit the question asks for; the real test may need it. [S5]
- Round only at the end, and only as the question says.
- Ask whether the answer is a sensible size before you type it. Four tablets or 250 mL from one ampoule is a warning sign.
- Keep to 2 minutes a question at most. [S4]