ACCESS TO NURSING SHEET 8
SI UNITS
The SI (Systeme International d'Unites) is a globally agreed system of units based on the metric system.
MASS - The base unit of mass (what is often termed weight) is the kilogram, which was first designed as the mass of a cube of water with sides of one-tenth of
The SI system consists of 7 base units:
Basic quantity
Mass
Name Symbol kilogram kg a metre (which equals a litre). Very small objects are weighed in milligrams.
Medicines are usually weighed in milligrams. Very heavy objects are weighed in metric tonnes. There are:
Length metre m
Time
Electric current
Temperature second s
Ampere A
Kelvin K
Amount of substance mole mol
1000 micrograms (μg) = 1 milligram (mg)
1000 milligrams (mg) = 1 gram (g)
1000 grams = 1 kilogram (kg)
1000 kilograms = 1 tonne (t)
Big units to small units: multiply by 1000
Small units to big units: divide by 1000
Luminous intensity candela cd
SI Prefixes
SI prefixes are used to form decimal multiples and submultiples of SI units.
The prefix attaches directly to the name of a unit, and a prefix symbol attaches directly to the symbol for a unit. Here are the most commonly used:
Multiplying Factor
1 000 000 000 000 tera (T)
1 000 000 000
1 000 000
1 000
0.001
0.000 001
0.000 000 001
SI Prefix
(symbol) giga (G) mega (M) 10 6 kilo (k) milli (m)
Scientific
Notation
10 12
10 9
10 3
10 -3 micro (µ) 10 -6 nano (n) 10 -9
EXERCISE 1
Change the following as indicated.
1 780 mg to g 8 8.98 g to mg
2 8 mg to g 9 5.26 kg to g
3 1500 g to kg 10 8.5 kg to g
4 0.103 mg to μg 11 70 μg to mg
5 338 μg to mg 12 950 mg to g
6 12 μg to mg 13 55 mg to g
7 0.010 mg to μg 14 0.075 mg to μg
15 A child is prescribed a drug at the rate of 35 mg for each kg of weight.
Calculate how many mg are required for each dose if the child is 18 kg.
16 How many 50 mg tablets should be given for a dose of 0.1 grams?
17 A tablet contains 100 microgrammes.
How many tablets will provide 0.25
mg?
18 A tablet contains 250 mg of soluble aspirin. What dosage would provide
125 mg?

CAPACITY - is a measure of the amount of space that a liquid takes up. The litre is the volume of a cube 10 cm x 10 cm x 10 cm = 1000 cm 3 . Medicine spoons normally hold 5 millilitres. Cans of Cola usually hold 330ml. Big bottles of pop hold 2 litres. Sometimes the centilitre is used.
There are:
10 millilitres (ml) = 1 centilitre (cl)
100 centilitres = 1 litre (l)
1000 millilitres = 1 litre
EXERCISE 2
Change the following as indicated.
1 3278 ml to litres 6 1.332 litre to ml
2 8250 ml to litres 7 7.6 litres to ml
3 9300 ml to litres 8 0.755 litres to ml
4 6035 ml to litres 9 0.32 litres to ml
5 5020 ml to litres 10 0.1 litres to ml
11 How many cl are there in ½ litre?
12 How many 5 ml spoonfuls would make up 1 cl?
13 100 bottles each holding ½ a litre are filled from a container holding 150 litres. How much is left in the container?
LENGTH - The base unit of length is the metre. The metre was first designed as one ten-millionth of the distance between the North Pole and the equator. A metre is roughly the length of a large pace, or the depth of the shallow end of a swimming pool. There are:
10 millimetres (mm) = 1 centimetre (cm)
100 centimetres = 1 metre (m)
1000 metres = kilometre (km)
1000 millimetres = 1 metre
EXERCISE 3
Change the following as indicated:
1 357 cm to m 6 9137 m to km
2 3760 cm to m 7 3372 m to km
3 60 cm to m 8 19.6 km to m
4 5276 mm to m 9 9.2 m to cm
5 80 mm to m 10 8.21 m to mm
11 A syringe has a diameter of 26.5 mm.
What is its diameter in cm?
12 Add 200 m, 500 m and 350 m giving
your answer in km.
13 Choose the most appropriate metric unit to measure:
a the height of a building
b the capacity of a bottle of ink
c the weight of a baby
d the length of a car journey.
UNITS OF DRUG AMOUNT – THE
MOLE
The base unit for an amount of drug is the mole. One mole is the amount of substance containing 6.02 × 10 23 of its component formula units (e.g. atoms, molecules or ions). The number of moles of a drug may easily be expressed as a mass since a mole of a drug weighs, in grams, the same as the relative molecular mass (RMM) of the substance. Thus, for example, 1 mole of potassium chloride
(RMM= 74.5) weighs 74.5 grams.
1000 micromoles (μmol) = 1 millimole (mmol)
1000 millimoles (mmol) = 1 mole (mol)
EXERCISE 4
Change the following as indicated:
1 2 moles to millimoles
2 5.2 moles to millimoles
3 3000 millimoles to moles
4 4236 millimoles to moles

5 5000 micromoles to millimoles
6 9876 micromoles to millimoles
7 6 millimoles to micromoles
8 4.7 millimoles to micromoles
INFUSION RATES
Health care professionals are regularly required to set and check the rate of drip of an Intravenous Set. To carry out this extremely important function, a knowledge of metric weights and capacities is needed, together with confidence in multiplication and division of decimals.
The rate of drip to be set depends on the amount of solution required, the number of drops to provide that solution, and the length of time specified.
IV sets generally use 15 drops per ml, 20 drops per ml, or 60 drops per ml (used in
Paediatrics).
Use the formula
Drip rate = no. ml x no. drops per ml ÷ time in mins and round any decimal answers to the nearest whole drop
EXERCISE 5
1 An IV set delivers 20 drops per ml. If
0.5 ml of solution must be given every minute, calculate the drip rate.
2 A 500 ml transfusion of blood is to be given over 3 hours. Assuming an intravenous set rate of 15 drops per ml, find the required drip rate in drops per minute. (Round your answer to the nearest whole drip)
3 100 ml of fluid is required over 1 hour.
Find the drip rate per minute required using an IV set delivering 20 drops per ml.
4 A child is prescribed 200 ml of solution over four hours. The IV set delivers 60 drops per ml. Find the required drip rate in drops per minute.
5 An IV set delivers 20 drops per ml at a rate of 10 drips per minute. Find the time taken to deliver 200 ml.
EXERCISE 6 - CONVERSIONS
BETWEEN METRIC AND IMPERIAL
UNITS
2 pounds is slightly less than 1 kilogram
4 oz is slightly more than 100 grams
1 Is 1 oz nearly equal to 3 g, 30 g, 300g or 3 kg?
2 Is 1 kg more or less than 2 lb?
3 Give in pounds the approximate weight of a 4 kg newborn baby.
1 litre is approximately 1¾ pints
30 ml is approximately 1 fl oz
4 Are 2 pints more or less than 1 litre?
5 Are 120 ml approximately equal to 1, 2,
3 or 4 fluid ounces?
6 Is there more cream in a 5 fl oz pot than a 135 ml pot?
1 inch is slightly more than 2½ cm
1 foot is approximately 30 cm
1 yard is slightly less than 1 metre
7 Is 1 m longer or shorter than 1 yard?
8 How many inches are approximately equal to (a) 10 cm (b) 5 cm (c) 20 cm?
9 How many cm are approximately equal to (a) 3 ft (b) 1’6” (c) 6 in?