How CMS Pulse Oximeters Work

By Georgia Diaz


CMS pulse oximeters are the little medical devices that they plug onto your fingertip whenever you go to the Emergency Room or before an operation. Sometimes they put them onto the earlobes. In tiny babies, they use a foot. The purpose of the device is to measure the percentage of hemoglobin that is saturated with oxygen. Generally, this number should always be at 95% or higher.

The physical principles of how a pulse oximeter works are beyond the scope of this article. It is based on the absorbance of light. By shining light of two different wavelengths into the skin, the instrument can calculate the light absorbance, and hence the concentration of O2 in blood that is circulating in the arteries.

While this is a decent method of measuring oxygen saturation, it gives no information about the actual level of oxygen in the blood. More accurate measurements of blood oxygen levels may be obtained by measuring arterial blood flow. The best method of doing this is by sticking a needle directly into an accessible artery.

They need a good reason to measure arterial oxygen levels because placing the needle into an artery is very painful to the patient. This is fine if the person is unconscious, as if they were under an anesthetic or unconscious. If they are awake and aware, it feels like someone is plunging a needle directly into bone.

One of the circumstances where pulse oximetry is employed is during sleep studies. These investigations require an overnight stay in the hospital and are done for the purpose of finding out if someone has a condition called sleep apnea. This is when a person periodically stops breathing during the night. At best, they wake up drowsy and fuzzy-headed. At worst, it is a risk factor for life-threatening conditions like heart attack and stroke.

There are two basic forms of sleep apnea; neurological (or central) and obstructive sleep apnea (OSA). Of these, OSA is the more common and the easiest to treat. Some people need surgery to correct an anatomical abnormality, while others are easier to treat with continuous positive airway pressure (CPAP) or wearing an oral device, prescribed by an oral surgeon, while thy sleep.

Central, or neurological sleep apnea, is less common and harder to treat than OSA. Instead of stopping the breathing process, the brain doesn't attempt it. There is often a serious condition underlying neurological OSA that affects the brain stem. This is the brain area that is responsible for breathing and heart rate. Neurological sleep apnea can happen by itself or in combination with OSA.

Although anyone can have any type of sleep apnea, the major risk factors are male gender over the age of 40 and being overweight. Sleep apnea is particularly dangerous in infants, who can stop breathing for as long as twenty seconds. This is a very daunting prospect for new parents. Fortunately, there are apnea alarms available that will alert the parents when a baby stops breathing for a set number of seconds. It is also possible to obtain CMS pulse oximeters for home use.




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