From your readings in module 2, you would realize the importance of correct drug calculations. In this module you are going to look at drug calculations that you will encounter next year and in your career when you have to revisit these calculations. You don’t have to solve these problems (you can if you wish) but to critically study them to understand what they are asking and extract the information needed.
On successful completion of this module you should be able to:
Here is a transcript of part of this video.
Susan: Gee you don’t have to do much calculating here. All the machines do it for you and the doctor tells you what dose to give..It’s all on the labels.
Nurse 1: Um...most of the time it is relatively straight forward. But you’ve gotta know what your doing. They’re pretty hot on calculating doses ‘cos it can be really bad if they’re wrong. We have to pass a test before we start - and once a year after that.
Susan: Sounds like a waste of time to me. Must get everybody all worked up for nothing. Well at least I can use my calculator.
Susan sees Mary-Anne passing. She looks worried, and is in a hurry.
Susan: Can you excuse me for a minute - there’s a friend of mine ...
Nurse 1 nods assent. Susan follows Mary-Anne to a casualty booth. Danny and another two nurses are in there. A doctor has been examining Danny’s arm. A nurse takes Danny to the scales.
Susan: Mary-Anne - what happened?
Mary-Anne: (Surprised) Oh Susan. Danny fell of his bike - they think his arm’s broken.
Nurse 2: How heavy are you Danny?
Danny: About forty Kilos.
Nurse 2: (Weighing) That’s right Danny. Forty Kilos.
Doctor: Right Danny - we’d better give you something to ease the pain. How much did we say you weighed?
Dan: 40 kilograms (looking exasperated)
Doctor: Well yes....we need your weight so we can calculate the exact amount of painkiller for you. (to nurses) Give him 15 milligrams IV pethidine.
Nurse 2: Cathy can you check again the standard dose with me? (Nurse 3 (Cathy) looks up the MIMS with Nurse 2 looking on.)
Cathy: point five to 1 milligrams per kilogram dose for IV point five times 40 is 20 milligrams. It’s a bit on the low side. Is that OK? (To the doctor)
Doctor: Yep. That’s fine.
Nurse 2: We’ve got to give 15 milligrams from the ampule. OK, let’s work out how much we have to draw up.
Susan: I thought you’d just worked that out.
Nurse 2: We worked out a weight. We need to know the volume to draw from the ampule. We have to calculate the amount.
Nurse 2: Let’s see. There’s 50 milligrams in a millilitre (Nurse 2 does the calculation on paper) so for 15 milligrams we divide 15 by 50 then multiply that by one millilitre - equals point three).
(Cathy and Susan look on and agree. Susan still looks confused but goes along with the other nurses. (The calculation reads 15 mg/50 mg x 1 mL = 0.3) Then Nurse 2 draws up 0.3 mL from the ampule into a syringe and prepares to give it to Dan in a vein....scene fades)
Let’s have a closer look at some drug questions. One of the most important skills you need is being able to interpret the question correctly. Try this exercise.
When you perform drug calculation problems you will need to interpret what type of question it is. Have a look at the flow chart below. You start by asking yourself what type of drug therapy it is. Look for phrases like “volume to deliver”, “infused over two hours”; “calculate the rate” etc. All these involve infusion therapy. This will be a RATE. You then need to identify the type of infusion - will it be in mLs per hour or drops per minute? The photo to the left will deliver mL per hour. The one on the right will deliver in drops per minute.
If it is a medication, then it may be tablets or liquid. Both the liquid and the tablets have different strengths and you need to identify the strength.
For example on the left the label states:
So the container itself has 10 millilitres of fluid. In each millilitre there is 100 Units of Protaphane.
On the right the box states:
So the box has 30 tablets. In each tablet there is 40 milligrams of the drug atorvastatin.
In drug calculation written problems you also need to highlight the information given in the problem and determine if any information is irrelevant.