What could explain an unusually high arterial oxygen level for a patient breathing room air?

The presence of air bubbles in an arterial blood gas sample can lead to an artificially high arterial oxygen level. When a sample contains air bubbles, the oxygen in the bubbles can mix with the blood, resulting in a reading that does not accurately reflect the patient's true arterial oxygen level. This phenomenon occurs because the air bubbles introduce extra oxygen into the sample, skewing the measurement higher than it should be based on the patient's actual respiratory status.

Other factors, while relevant in the context of arterial oxygen levels, do not directly lead to an artificially high reading in the same way. For instance, blood coagulation can affect the sample's usability but does not inherently increase oxygen levels. Normal ventilation and perfusion (V/Q) matching would typically reflect appropriate oxygenation based on the individual's respiratory dynamics, thus not causing a marked increase. Hyperventilation can raise oxygen levels in the blood, but not to an unusual degree as seen with sample contamination from air bubbles. Therefore, air bubbles present in a blood sample are the most likely explanation for an unusually high arterial oxygen level when the patient is breathing room air.