CMS pulse oximeters are medical gadgets that help
medical professionals determine, somewhat indirectly, if
a patient is getting enough oxygen. The devices clip onto
the finger, the earlobes or, in infants, a foot. What they
actually measure is the amount of hemoglobin that is
fully loaded up with oxygen. In most people, this figure
should be at least 95% 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 is an excellent way of screening sick people
from really sick people, a more accurate measurement is
obtained by measuring oxygen directly from arterial
blood. This is important in places like intensive care
units or when a patient is under anesthesia having an
Jamming a needle into an artery, which are by design
very thick, is very painful for the patient. Because of
this, it is not routinely done unless it is really necessary.
The feeling of having a needle pierce into an artery has
been compared to having a sharp implement poking
directly into a 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 main types of sleep apnea, obstructive
and neurological. Obstructive sleep apnea (OSA) is the
more common of the two and is also the easiest to treat.
Therapies include surgery, continuous positive airway
pressure (CPAP) or prescribing a device that the patient
puts in their mouth when they go to bed that helps
them to keep their airway open.
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
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.