Hyperoxia test
Encyclopedia
A hyperoxia test is a test that is performed--usually on an infant-- to determine whether the patient's cyanosis
is due to lung disease or a problem with blood circulation.:141
It is performed by measuring the arterial blood gases of the patient while he breathes room air, then re-measuring the blood gases after the patient has breathed 100% oxygen for 10 minutes.:141 If the cause of the cyanosis is due to poor oxygen saturation by the lungs, allowing the patient to breath 100% O2 will augment the lungs' ability to saturate the blood with oxygen, and the partial pressure
of oxygen in the arterial blood will rise (usually above 150 mmHg). However, if the lungs are healthy and already fully saturating the blood that is delivered to them, then supplemental oxygen will have no effect, and the partial pressure of oxygen will usually remain below 100mmHg. In this case, the cyanosis is most likely due to blood that moves from the systemic veins to the systemic arteries via a right-to-left shunt
without ever going through the lungs.:141
Cyanosis
Cyanosis is the appearance of a blue or purple coloration of the skin or mucous membranes due to the tissues near the skin surface being low on oxygen. The onset of cyanosis is 2.5 g/dL of deoxyhemoglobin. The bluish color is more readily apparent in those with high hemoglobin counts than it is...
is due to lung disease or a problem with blood circulation.:141
It is performed by measuring the arterial blood gases of the patient while he breathes room air, then re-measuring the blood gases after the patient has breathed 100% oxygen for 10 minutes.:141 If the cause of the cyanosis is due to poor oxygen saturation by the lungs, allowing the patient to breath 100% O2 will augment the lungs' ability to saturate the blood with oxygen, and the partial pressure
Partial pressure
In a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume. The total pressure of a gas mixture is the sum of the partial pressures of each individual gas in the mixture....
of oxygen in the arterial blood will rise (usually above 150 mmHg). However, if the lungs are healthy and already fully saturating the blood that is delivered to them, then supplemental oxygen will have no effect, and the partial pressure of oxygen will usually remain below 100mmHg. In this case, the cyanosis is most likely due to blood that moves from the systemic veins to the systemic arteries via a right-to-left shunt
Right-to-left shunt
A right-to-left shunt is a cardiac shunt which allows blood to flow from the right heart to the left heart. This terminology is used both for the abnormal state in humans and for normal physiological shunts in reptiles...
without ever going through the lungs.:141