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

In the 2013 guidelines NICE recommend the following requirements for maintenance fluids:

• 25-30 ml/kg/day of water and
• approximately 1 mmol/kg/day of potassium, sodium and chloride and
• approximately 50-100 g/day of glucose to limit starvation ketosis

So, for a 80kg patient, for a 24 hour period, this would translate to:

• 2 litres of water
• 80mmol potassium

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.

The table below shows the electrolyte concentrations (in millimoles/litre) of plasma and the most commonly used fluids:

Specific points

0.9% saline

• if large volumes are used there is an increased risk of hyperchloraemic metabolic acidosis