Asthma - Testing Oxygen levels
Assessing enrichment of the blood with oxygen by the lung can be made by a noninvasive technique called oximetry, in which a sensor placed on the fingertip or earlobe can accurately measure oxygen saturation. Such a sensor is often immediately placed on an asthmatic patient who has been admitted to an emergency room. Oxygen saturation testing measures how much oxygen the blood has acquired in the air sacs of the lungs.
The oximeter transmits different wavelengths of light through small blood vessels called capillaries. The fingernail and earlobe are used since these small vessels are close to the surface of the skin. In these small blood vessels oxygen is carried by a protein called hemoglobin. As oxygen is used by the body, the hemoglobin undergoes a change that can be detected by a different absorption of light from the oximeter. This determine is made during each pulse beat and from the relative amounts of hemoglobin with and without oxygen, the saturation is determined. The patient’s pulse is also recorded.
This technique can be extremely helpful in evaluating bronchial asthma since oxygen levels will typically fall with significant degrees of airway obstruction. An asthma attack that reduces oxygen levels signifies a more severe episode and calls for aggressive medical treatment. Oximetry is painless and does not require blood sampling.
