An Explanation Of CMS Pulse Oximeters

By Georgia Diaz


When doctors, nurses or paramedics need a quick estimate of a patient's oxygen levels, they use technology called CMS pulse oximeters. These little gadgets can be easily clipped onto a finger or an earlobe and indirectly measure oxygen levels by determining the percentage of hemoglobin, a respiratory pigment, that is saturated with the life-giving gas. Normal values in most people are 95 percent or more.

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 technology can reveal the oxygen saturation of a person's hemoglobin, it is at best an indirect means of finding out how much actual oxygen is circulating in the bloodstream. To measure this directly, it is necessary to sample the blood passing through the arteries in real time. This involves placing a needle into an artery.

This is a painful and invasive procedure and there needs to be a good reason for collecting this information. Patients who have their arterial blood sampled while they are awake describe the sensation as akin to having a needle stuck directly into their bone. Unfortunately, because one of the circumstances in which this information is important is while a patient is under an anesthetic, so the poor patient has to have the needle inserted while they are still awake.

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.

The other form of sleep apnea, central, is less common and potentially more serious than OSA. This is because the center of the brain that regulates physiological processes like heart rate and breathing, malfunctions to the point where the body won't try to breathe. Either type of apnea may occur on its own or in conjunction with the other form.

Anybody can be diagnosed with either form of sleep apnea. The principal risk factors are age over 40, obesity and being male. This is a particularly heart-breaking condition in young babies, who can sometimes stop breathing for periods as long as 20s. This is frightening for new parents. Fortunately, alarms are available that can sound an alert when the baby has an apnea episode. CMS pulse oximeters may also be purchased for use at home for both adult and child use.




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