Capillary blood gas measurements
Blood gas analysers can measure pO2 (partial pressure of oxygen) levels accurately on all types of appropriate samples, e.g., arterial or venous blood, or tidal gas flow samples.
However, measurements of capillary blood gas oxygen are not recommended. This is due to:
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collection difficulties- the ability to maintain anaerobic collection conditions is almost impossible when collecting capillary blood into a capillary blood collection tube. Compare this to a hypodermic needle arterial stab, when no ambient oxygen is able to contaminate the sample.
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peripheral perfusion variations- due to varying temperature of hands or heels. Oxygen tension is markedly affected by peripheral blood flow and the coldness of hands or feet.
On the other hand, the partial pressure of carbon dioxide, pCO2, compares well in capillary and arterial samples and may be measured accurately in capillary blood samples. CO2 tends to diffuse more slowly than O2 and ambient levels of CO2 are far closer to capillary blood levels than are O2 levels.
