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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
  • HCO3- 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.