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)