Fluid balance calculations
1 mark of the 15 in Part A, which runs for 30 minutes.
Fluid balance is arithmetic with a clinical judgement attached. Add the intake, add the output, subtract, and say whether the patient is running positive or negative. The marks are lost in what gets left out of the two columns.
What this section asks about
- Totalling intake, including oral fluids, intravenous fluids and the volume that intravenous medicines carry
- Totalling output, including urine, drains, vomit, stoma and estimated insensible losses
- Reporting a balance with its sign, positive or negative
- Percentage dehydration and fluid deficit from a change in body weight
Where the marks go
1 mark 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
- Forgetting that intravenous antibiotics are intake. Three 100 mL doses is 300 mL in.
- Dropping insensible losses when the question has given them to you.
- Reporting the size of the balance without its direction.
Questions people ask
- How much fluid balance is in the CBT?
- It is the smallest of the six numeracy categories in the test specification, but it is on the paper, and it is the one people practise least.
- How is percentage dehydration worked out?
- Weight lost divided by the pre-illness weight, times 100. In a child, each 1% of body weight lost is roughly 10 mL per kilogram of deficit.
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.