ABG

What is it?

Arterial Blood Gases (or ABG) is a blood test taken from an artery, then analysed to find out the concentrations of various gases disolved in it.

What is measured?

The standard blood gas profile is:

• pH 7.35-7.45
• PaO₂ 10-13 kPa
• PaCO₂ 4.5-6 kPa
• HCO_3- 22-25 mmol/L
• Base excess -2 to +2

What it means?

ABGs are used to work out acidosis and alkalosis. There is lots about this on the acidosis & alkalosis page, but in summary:

1. Is the pH high or low? - low pH= acidosis and high pH = alkalosis.
2. Is CO₂ abnormal? - if so, is this in keeping with the pH change? - i.e. when pH↑, CO₂↓ or pH↓, CO₂↑. These changes point to a respiratory acidosis/alkalosis. If there is no abnormality in CO₂, it may be there has been a compensatory change.
3. Is the HCO₃^- abnormal? - if so, is this in keeping with the pH change? - i.e. (opposite to CO₂ changes) when pH↑, HCO₃^-↑ OR pH↓ HCO₃^-↓ then the change is metabolic. Otherwise, there may again have been a compensatory change.