OSCE calculations for vets: worked examples for fluid rates, doses and tablets

Updated 20 October 2026

Maths is a common reason for lost marks, mostly through unit slips under pressure. Practise the same four sums until the steps are automatic, and say your working aloud. These examples are for practice only: always check the datasheet for real dosing.

Fluid rate over 24 hours

A 20 kg dog is 5% dehydrated. Maintenance is 50 ml/kg/day and there are no extra losses. Replace the deficit and give maintenance over 24 hours.

Deficit = 20 x 0.05 x 1000 = 1000 ml.
Maintenance = 20 x 50 = 1000 ml.
Total 2000 ml over 24 hours = 83 ml/hr.

Injection volume

Give meloxicam at 0.2 mg/kg to a 10 kg dog. The bottle is 5 mg/ml.

Dose = 10 x 0.2 = 2 mg.
Volume = 2 / 5 = 0.4 ml.

Tablets to dispense

Give 10 mg/kg once daily to a 20 kg dog for 7 days using 100 mg tablets, rounding to the nearest half tablet.

Dose = 20 x 10 = 200 mg, which is 2 tablets.
Total = 2 x 7 = 14 tablets.

Fresh gas flow

A 15 kg dog, breathing 15 times a minute, on a Bain circuit with a system factor of 2.5 to 3.

Tidal volume = 15 x 10 = 150 ml.
Minute volume = 150 x 15 = 2250 ml/min.
Flow = 2250 x 2.5 to 3 = 5.6 to 6.75 L/min.

Habits that protect your marks

Write the units on every line.
Check the answer is sensible: a 2 ml injection for a 10 kg dog is not.
Say the working aloud so the examiner can follow it.
Re-read the question for the unit it asks for.

Frequently asked questions

What calculations come up in a vet OSCE?

Common ones are fluid rates, drug volumes, tablets to dispense and fresh gas flows. Practise them until the steps are automatic.

How do I calculate a fluid rate in ml/hr?

Add the deficit (weight x percentage dehydrated x 1000) to the maintenance volume, then divide by the hours over which you will give it.

Keep reading

Official sources

RCVS: Statutory Membership Exam