Injection and reconstitution calculations
3 marks of the 15 in Part A, which runs for 30 minutes.
An injection question gives you an ampoule or a vial and asks for a volume. Reconstitution is where these get interesting, because the concentration you divide by is the one after the diluent has gone in, not the amount printed on the vial.
What this section asks about
- Drawing up part of an ampoule, given a strength per millilitre
- Reconstituting a powder and working out the concentration that results
- Doses per kilogram that then have to become a volume
- Recognising a volume too large for one intramuscular site
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.
Where candidates lose marks
- Dividing by the vial contents instead of the concentration after reconstitution.
- Ignoring what the answer means in practice. More than 2 to 3 mL in one intramuscular site in an adult is divided between two sites.
- Losing a decimal place on a small volume. 0.25 mL and 2.5 mL are a tenfold difference.
Questions people ask
- Do I need to know displacement values?
- The question gives you what you need. If it tells you the reconstituted concentration, use it; if it tells you the diluent volume, work the concentration out from it.
- Are injection questions harder than tablet questions?
- They have more steps, which is where the marks go rather than in the arithmetic. Write the steps down on the note board instead of holding them in your head.
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.