Before interpreting the capillary blood gas result, it’s vital to look at the patient’s clinical status because this will provide important context to the result.

Lets look at some examples where the patient’s clinical context is important when interpreting the test results:

• If the patient has a normal PaO₂, we might consider this unremarkable. However, you cannot interpret PaO₂ without knowing the inspired oxygen concentration (FiO₂). If the patient is on high flow oxygen, you would expect their PaO₂ to be abnormally high, so a PaO₂ in the normal range is probably abnormal.
• During an acute asthma attack, there is significant bronchoconstriction which leads to hypoxia (low PaO₂). In an effort to normalise their PaO₂, patients tend to hyperventilate which has the effect of lowering their PaCO₂. Therefore, if their PaCO₂ begins to rise (back to normal levels), this suggests they are tiring and may need ventilatory support
• In a patient with an abnormally low PaO₂, they might be diagnosed with Type I Respiratory failure. However, before jumping to this diagnostic conclusion, if the patient looks well with a normal SpO₂, we should first eliminate the possibility of a pre-analytical error (for example a non-arterialised ELCBG sample)