Portable Oxygen: A
Oximeters: Part 1
The information here provided
educational purposes only and it is not intended, nor implied, to be a
for professional medical advice. Always consult your own physician or
healthcare provider with any questions you may have regarding a medical
is a Pulse Oximeter?
called a "pulseox," is a
noninvasive device used to measure pulse rate and oxygen saturation.
It reports the amount of oxygen currently carried by
arterial blood as a percent of the maximum amount the blood can carry.
It also records and reports pulse rate. An oximeter probe is
typically clipped to a
finger or ear lobe, or is attached to the body with adhesive. It has a
sensor that measures the light passing
through the skin and reports the saturation and pulse rate, either
printing the reading.
tests to determine oxygen
saturation-- the level of oxygen
blood. They are the arterial blood gas (ABG) test, co-oximetry, and
- Before the oximeter, the ABG test and co-oximetry
were the only two methods of
saturation. A technician performs an ABG by inserting a needle into an
artery and taking a blood sample. The artery chosen for this test may
be the radial artery at the wrist or the brachial artery on the elbow.
An examination of the blood sample provides several
measures, including the amount of oxygen and carbon dioxide and its pH.
- Since the 1980s, pulse oximetry has become available
measurement method. Whereas the ABG test continues to be used, it has
its drawbacks when it is used strictly to determine oxygen saturation.
It is invasive and is administered only in a medical facility by
professional staff. It cannot be administered during sleep; the
is wide-awake and sitting up. To assume that a single reading
represents the patient’s
oxygen level at other times and under other conditions is expecting
more of the ABG than it can deliver.
Georg Gabriel Stokes
hemoglobin is the carrier of
oxygen in the blood.
1876 Karl von Vierordt uses a light source to
distinguish fully saturated blood from that which is not.
1941 "Oximetry testing" is is first used to identify the
of obtaining saturation readings with an pulse oximeter.
1940s Oximetry testing saves WW II pilots who fly aircraft that lack
1970 Oximetry becomes clinically feasible.
1980s Oximeters become smaller in size, easier to use, and lower in
1995, "Finger" oximeters, small enough to perch on a finger, first
appear on the market.
physicians' billing for in-office oximeter readings.
oximeters of the 1970s weighed 25 pounds and was transported on a cart.
Its sensor on the end of a long cord weighed 3 pounds, looked like a
large C clamp, and was very uncomfortable when attached to the
patient's ear. With that, oximetry
testing became the fifth measure of vital signs, the
first four being temperature, respiration, pulse rate, and blood
First Encounter With an Oximeter
spring of 1998,
was in the hospital for the second
time in as many months because my body could not support both my normal
breathing and the coughing which accompanied my lung infection. I
remember being awakened the third day to find both my primary care
doctor and pulmonologist standing at the foot of my bed. Both smiling,
they asked if I was ready to give up smoking. With the two bouts of
coughing clear in my mind, I knew there was only one choice. I nodded
remember is walking very fast down the hospital
hallway. One of my hands was busy keeping the back of my hospital gown
while on the index finger of the other was a clamp with a wire coming
out from it. At the other end of the wire was a nurse who was trying to
keep pace with me. She was carrying a device the size of a large
dictionary that she cradled in her arms. Her objective, she
kept muttering was to get this device to give her the Medicare number
she wanted before she ran into a wall or was tripped up by the
carpeting. As we walked, her defense was to keep her eyes moving more
her feet--from the numbers displayed on that device, to the
connecting wire, to the floor in front of her. I later learned the
number she was seeking would qualify me for supplemental oxygen under
have been a
funny sight to those in that hallway. Perhaps you
too were first introduced to a pulseox while scurrying down a
hospital hallway with one hand behind you, holding your gown closed.
purchased my own pulseox. It was a relatively
inexpensive and, gratefully, much lighter-weight version of the device
used by that nurse. In 2002, I responded to an Internet survey of
oxygen users, indicating that I owned a pulseox, as did 61
percent of the other respondents.
I took my
home and quickly "trained" it, or so I
thought. When I
huffed and puffed, the pulseox would dutifully display a saturation
reading below 90 percent and when my breathing was normal, it would
show a reading above 90.
supplemental oxygen use for those who
demonstrate saturation levels at 88% or lower as measured by an
dependent edema, polycythemia, or cor pulmonale is also present, a
patient can meet the Medicare requirement with a saturation level of
89%. Some patients may not qualify for oxygen therapy at rest but can
qualify for oxygen during ambulation, sleep, or exercise.
Advice for the Patient?
as I became
more dependent on my pulseox I became more critical of the numbers it
displayed. I found times when I was not huffing and
puffing and yet my pulseox displayed a saturation of less than
90 percent. I found other times I did huff and puff that it displayed
saturation above 90 percent. Was my pulseox broken? Should I trust my
pulseox or the huffing and puffing? Did I not fully understand the
capabilities? What was going on?
"expert" advice, first in the manual that
accompanied the oximeter and there was nothing there. A lot of advice
about how to
use and maintain it but nothing about what the numbers it displayed
meant to my
health. I next searched the Internet for helpful advice. What I found
were research studies that used oximeters or training materials for
in which doctors or respiratory therapists talked to patients about how
use an oximeter? I found one written by Dr.
Fred Furgang, but
it was directed at healthy
airline pilots who use oximeters when they "reach for the stars" with
oxygen but no cabin pressure. I rcently for a second source entitled Tips for Using Oximetry in Home Oxygen Therapy that was written by Brent Blue, M.D.
occurred that helped me better understand the
advantages and shortcomings of my huffing and puffing as a medical
alert signal, as well as the advantages and shortcomings of my pulseox.
outlandish readings when it first starts up. Ignore these
readings. Valid readings will begin to appear about ten (10) seconds
after you first see numbers displayed. Your pulseox displays
rolling averages of both pulse and saturation readings. The device
needs about ten seconds to accumulate enough good readings to display a
For nearly five years my pulseox has been my constant companion,
dangling from its lanyard around my neck, strategically placed so it
can catch the food that doesn't reach my mouth, and always available to
be popped on my
finger at any time. I check my "sat" several times a day for several
- I take readings after both showering and dressing in
morning. These are events I perform in a routine manner. For this
reason my sat should not vary day to day when I am using the same
level of supplemental oxygen. What I don't want to see are higher pulse
rates and lower saturation readings. Things I have no control
over--the weather, atmospheric pressure, and pollen, can
cause some variations, but so can lung infections. Abnormal pulseox
readings tell me to check symptoms of respiratory exacerbations--a dry
nonproductive but persistent cough, excessive and/or discolored sputum,
wheezing, breathlessness or chest tightness--and take proper action.
written to express their concern about how slowly the oximeter
readings sometimes move from the 80s back into the 90s. If you have
that the readings move more quickly from the low to the middle 80s and
much more slowly from the middle 80s to 90, do not despair. There is
nothing wrong with your oximeter. This is the way it is supposed to
work. Saturation percentages are not based on numbers but on their
logarithms. If you want to know more about this, look under "Theory of
Operation" in the operator's manual. No lecture from me today on
- I also take readings when I feel my pulseox reading
be below 88 percent. When my saturation reading is below 88 percent, I
continue to monitor my saturation until it is back in the 90s. I
increase oxygen output to speed the recovery process and I make note of
the time it takes to recover.
Up until a
years ago, the only reason I used the pulse reading was to compare my
actual reading with the expected reading during exercise at Pulmonary
Rehab. Normal pulse rate for me ranged from the 80s to as high as 120.
More recently, I have found the pulse readings became predictors of
problems I was having with my heart. Abnormal readings sent me to my
physician to determine what the problem was and what to do about it, if
About the time I experienced significant edema--enough to require 120
mg of a diretic--I noticed my pulse rate would drop into the 40s for a
time and I would become breathless until it rose again. This would
occur even though my satuation was in the 90s.They tell me that arrhythemia like this
are not dangerous in a normal heart.
More recently, I experienced pulse rates of 150 -250. On three
occasions, this rate remained with me for over 20 minutes, which
encouraged me to get into the emergency room right away. I was having
SVTs (Super Ventricular Tachycardia), which are not so benign. After
wearing a heart monitor for a month, it was determined that my basic
problem was atrial fibrillations, a much more serious problem.
There is medication for atrial fibrillations but it did not agree with
me. I therefore got a fancy pacemaker, called an implantable cardiac
device (ICD), which not only regulates my heart but also has a
defibrillator in it to shock life back into it should my heart stop.
I never thought that my oximeter would provide me with advanced notice
of such a dangerous condition.
I have more to say about oximeters and will do so shortly in Part 2.
Peter M. Wilson, Ph.D.
Founder of PortableOxygen.org
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