There are two ways to answer this question. Firstly, we know that the daily sodium requirement is 70-150mmol. We can convert this to mg by multiplying by 58.5 (molecular weight of sodium is approximately 23, chloride is 35.5).

N.B. molecular weight of potassium is 39

So, 70-150mmol = 4095 - 8775mg = 4 - 8.5g. The nearest answer to this is 6g.

Secondly, this figure ties in with the governments recommended oral salt intake of 6g/day.

Fluid therapy

The prescription of intravenous fluids is one of the most common tasks that junior doctors need to do. The typical daily requirement is:

• 1.5 ml/kg/hr fluid - for a 80kg man around 2-3 litres/day
• 70-150mmol sodium
• 40-70mmol potassium

This is why the typical regime prescribed for patients is

• 1 litre 5% dextrose with 20mmol potassium over 8 hours
• 1 litre 0.9% normal saline with 20mmol potassium over 8 hours
• 1 litre 5% dextrose with 20mmol potassium over 8 hours

The amount of fluid patients require obviously varies according to their recent and past medical history. For example a patient who is post-op and is having significant losses from drains will require more fluid whereas a patient with heart failure should be given less fluid to avoid precipitating pulmonary oedema.

Drop Factor:

10 drops/ml (blood set)

15 drops/ml (regular set)