Nursing Calculations Workbook - Middlesex University

[Pages:22]LDU Maths, Stats and Numeracy Support Metric Conversions

Here are some metric weights arranged in size order, starting with the biggest:-

Kg (kilogram) g (gram) mg (milligram) mcg (microgram)

Each one is a thousand (1000) times smaller than the one before. The same rule applies for the metric volumes below

L (Litre)

ml (millilitre)

If you want to convert from big to small you multiply by 1000 by moving the decimal

point 3 places to the right.

If you want to convert from small to big you divide by 1000 by moving the decimal

point 3 places to the left.

Example 1: Convert 7.5 kg to g

Answer 1: 7500 g

Example 2: Convert 7280 mcg to mg

Answer 2: 7.28 mg

Example 3: Convert 1.5 Litres to ml

Answer 3: 1500 ml

Example 4: Convert 55 ml to Litres

Answer 4: 0.055 litres

Try the following questions

1) Convert 4.56 g to mg

2) Change 75 mcg to mg

3) Convert 0.78 mg to mcg

4) Change 950 mg to g

5) Convert 0.5 Litres to ml

6) Change 452 ml to Litres

numeracy@mdx.ac.uk

Page 1

LDU Maths, Stats and Numeracy Support Metric Conversions

ANSWERS

1) 4560 mg 2) 0.075 mg 3) 780 mcg 4) 0.95 g 5) 500 ml 6) 0.452 Litres

numeracy@mdx.ac.uk

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LDU Maths, Stats and Numeracy Support

Giving the Correct Amount of Tablets

You can use the following formula to calculate how many tablets to give

Example: Your patient has been prescribed 400mg ibuprofen. The tablets available are 200mg. How many tablets do you give the patient? Answer:

400 2

200

Notice that the prescription and stock units (mg) must be the same.

Try the following questions

1) A patient has been prescribed 40 mg. The stock tablets you have are 20 mg. How many tablets do you give the patient?

2) A patient has been prescribed 0.06 mg. The stock tablets you have are 30 mcg. How many tablets do you give the patient?

3) The stock tablets you have are 600 mcg. A patient has been prescribed 1.2 mg. How many tablets do you give the patient?

4) A patient has been prescribed 750 mg TDD (total daily dose). The stock tablets you have are 250 mg. How many tablets do you give the patient in a day?

5) A patient has been prescribed 750 mg TDD in 3 divided doses. The stock tablets you have are 250 mg. How many tablets do you give the patient for a single dose?

6) A patient has been prescribed 200 mg every 4 hours. The stock tablets you have are 100 mg. How many tablets do you give the patient in a day?

numeracy@mdx.ac.uk

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LDU Maths, Stats and Numeracy Support Giving the Correct Amount of Tablets

ANSWERS

1) 2

2) 0.06 mg = 60 mcg 2

3) 1.2 mg = 1200 mcg 2

4) 3

5) 250

250 250 1

6) 6

200 x 6 = 1200 mg per day 12

numeracy@mdx.ac.uk

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LDU Maths, Stats and Numeracy Support Giving the Correct Amount for Injection

You can use the following formula to calculate volumes for injection

Example:

Your patient has been prescribed 50mg of pethidine as injection. The stock strength

available is 100mg in 1ml. How many ml do you give the patient?

Answer:

0.5 ml

Notice that prescription and stock units (mg) must be the same.

Try the following questions

1) A patient has been prescribed 2mg of Pethidine. The stock strength you have is 10mg/ml. How many ml do you give the patient?

2) 40 units of Insulin have been prescribed. It is dispensed as 100 units in 1ml. How much do you give?

3) Ampoules of Morphine contain 10mg in 2ml. What volume must be drawn up to give 8mg?

4) The patient needs 250 mcg of Drug X. You have 1 mg in 1 ml. How many ml do you give?

5) 0.6mg of drug X is required. Stock is 0.4 mg in 2 ml. What volume do you give?

6) 0.25g of drug is ordered. Available stock on the ward is 500mg/5ml. Calculate the volume to be drawn up for injection.

7) 0.1 ml is given; it should have been 0.01ml. How many times too much is this?

numeracy@mdx.ac.uk

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LDU Maths, Stats and Numeracy Support Giving the Correct Amount for Injection

ANSWERS

1) 0.2

2) 0.4

3) 1.6

4) 0.25

5) . 3

.

6) 2.5

7)10 times too much. Every time the decimal point moves 1 place this is a factor of 10.

numeracy@mdx.ac.uk

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LDU Maths, Stats and Numeracy Support

Body Weight Calculations (single dose)

To work out the dosage based on the weight of the patient use the following formula

Dosage required = prescription x body weight

Example: Mrs B has been prescribed Ibuprofen 5mg/kg/dose. She weighs 60 kg. Calculate how much Ibuprofen you will give her. Answer:

5 mg x 60 = 300 mg

Note, the answer is never in kg (this only refers to the body weight)

Try the following questions

1) A patient has been prescribed Erythromycin, 40 mg/kg/dose. He weighs 74 kg. What is the dosage in mg?

2) A male patient weighs 90 kg and has been prescribed, 1.5 mg/kg/dose of drug X. How many mg will he need for a single dose?

3) Cloxacillin, 50 mg/kg/dose has been prescribed to a patient, whose weight is 45 kg. a) How many mg are required for a single dose? b) How many grams is this?

4) A female patient has been prescribed Chloramphenicol, 40 mg/kg/dose. She weighs 78 kg. How many grams of the drug does she require for each dose?

5) A patient weighs 60kg and requires 40 mcg/ kg of a drug. a) How many mcg are required? b) How many mg is this?

6) A patient who is 5 years old and weighs 20 kg has been prescribed 5 mcg per kilogram body weight of Digoxin elixir. The Digoxin elixir is available as 50 mcg per ml. a) How many mcg does the patient require per single dose? b) What volume will you give the patient at each dose?

numeracy@mdx.ac.uk

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LDU Maths, Stats and Numeracy Support Body Weight Calculations (single dose)

ANSWERS

1) 40 x 74 = 2960 mg

2) 90 x 1.5 = 90 + 45 = 135mg

3a) 50 x 45 = 2250mg 3b) 2.25 g

4) 78 x 40 = 3120mg = 3.12 g

5a) 60 x 40 = 2400mcg 5b) = 2.4 mg

6a) 20 x 5 = 100mcg 6b) 1 = 2 ml

numeracy@mdx.ac.uk

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