A pulse oximeter is a small device that can measure the oxygen
saturation in your blood. Pulse oximetry is a measure of how much oxygen
is in the blood.
Pulse
oximetry is a non-invasive method of measuring the oxygenation level in the
blood.
Pulse
oximetry is useful for people with chronic lung or heart conditions, who need
to monitor how well oxygen is being sent from the heart and lungs out to the
furthest parts of the body.
To
use a pulse oximeter, you'll clip the device on your toe, finger, or earlobe —
here's to use it properly so you can get an accurate reading.
Pulse
oximeters can be used to gauge warning signs for chronic lung or heart
conditions, and may help determine whether you should seek medical attention.
What does a pulse oximeter measure?
A pulse oximeter measures the oxygen saturation of your blood.
Essentially, this percentage is a calculation of how much oxygen is in the
blood, with 100% being 'fully saturated' and the optimal level.
And while this simple
non-invasive medical tool is available over the counter in many pharmacies,
it's not necessary for most people.
"Unless you have a chronic
heart or lung condition that affects your oxygen saturation on a regular basis,
most individuals don't need one in their home.
Those with lung or heart
conditions — such as chronic obstructive pulmonary disease (COPD) or heart
failure — may be prescribed home oxygen therapy by their doctor, and
a pulse oximeter can help them to monitor whether the use of oxygen at home is
improving their condition or not.
In fact, oxygen saturation by
itself is often not the best indicator of medical conditions, and other
symptoms are just as important to tell your doctor.
Other warning signs of low blood
oxygen levels may include:
- Increased heart rate
- increased breathing rate
- Feeling shortness of breath or gasping for air
- Inability to do an activity that you did before without
getting out of breath
How does a pulse oximeter work?
Every
system and organ in the body needs oxygen to survive. Without oxygen, cells
begin to malfunction and eventually die. Cell death can cause severe symptoms
and ultimately lead to organ failure.
The body
transports oxygen to the organs by filtering it through the lungs. The lungs
then distribute oxygen into the blood via haemoglobin proteins in red blood
cells. These proteins provide oxygen to the rest of the body.
Pulse
oximetry measures the percentage of oxygen in haemoglobin proteins,
called oxygen saturation. Oxygen saturation usually indicates how
much oxygen is getting to the organs.
Normal
oxygen saturation levels are between 95 and 100 percent. Oxygen saturation
levels below 90 percent are considered abnormally low and can be a
clinical emergency.
Oxygen
saturation can drop for many reasons, including:
- suffocation
- choking
- infections,
such as pneumonia
- drowning
- diseases, such
as emphysema, lung cancer, and lung infections
- inhaling
poisonous chemicals
- heart failure or
a history of heart attacks
- allergic
reactions
- general anaesthesia
- sleep apnoea
Pulse
oximeters work by shining a light through a relatively transparent area of the
skin. The light shines through to a detector positioned on the other side of
the skin.
For
example, when a pulse oximeter is clipped onto a finger, one side of the clip
shines the light, and the other detects it.
The
amount of light absorbed by the blood indicates the oxygen saturation. A pulse
oximeter does not directly measure oxygen saturation but instead uses a complex
equation and other data to estimate the exact level.
Benefits
Pulse oximeters are useful for
people who have conditions that affect oxygen saturation. For example, a sleep
specialist might recommend a pulse oximeter to monitor the night-time oxygen
saturation level of someone with suspected sleep apnoea or severe snoring.
Pulse oximetry can also provide
feedback about the effectiveness of breathing interventions, such as oxygen
therapy and ventilators.
Some doctors use pulse oximetry
to assess the safety of physical activity in people with cardiovascular or
respiratory problems, or may recommend that a person wears a pulse oximeter
while exercising. A doctor may also use pulse oximetry as part of a stress test.
Some hospitals also use pulse
oximeters for particularly vulnerable patients. For instance, infants in
neonatal intensive care units may wear pulse oximeters, which can alert staff
of a drop in oxygen saturation.
A drop in oxygen saturation in infants in neonatal intensive
care units may be detected using pulse oximetry.
Some benefits of pulse oximetry
include:
- monitoring
oxygen saturation over time
- alerting to
dangerously low oxygen levels, particularly in new-borns
- offering peace
of mind to people with chronic respiratory or cardiovascular conditions
- assessing the
need for supplemental oxygen
- monitoring
oxygen saturation levels in people under anaesthesia
- indicating
dangerous side effects in people taking drugs that affect breathing or
oxygen saturation
Pulse oximeters are now
widely available to buy online, so some people without specific risk factors
may use them.
What to expect
Pulse oximetry devices are non-invasive
and carry no serious risks. Some people experience minor irritation, including
skin redness and sensitivity.
If fitted very tightly and used
for a prolonged period, pulse oximeters can cut off oxygen from surrounding
vessels. Anyone who experiences numbness, tingling, or changes in skin color
should promptly notify a doctor.
The main risk of pulse oximetry
is a false reading. The accuracy of pulse oximeters depends on a correct fit,
and minor changes in their positioning can produce an inaccurate reading. A
person who rolls over in their sleep may loosen the device, causing it to give
a false alert.
Oxygen saturation may also dip
for brief periods due to other factors, such as a change in sleeping position
or momentary breath-holding. A pulse oximeter gives an alert even when the drop
is temporary and harmless.
For people with
health anxiety, or whose doctors have not helped them understand the role
of a pulse oximeter, this can cause unnecessary worry.
Conversely, pulse oximeters can
give some people a false sense of security. They do not provide alerts for all
possible oxygen issues, and cannot serve as a substitute for other forms of
monitoring.
People using pulse oximeters
should discuss the risks with a doctor and should maintain a record of the
readings over time. Changes in readings, particularly in response to
environmental changes, sometimes signal a health problem.
People interested in using
consumer-grade pulse oximeters should discuss their plans with a doctor before
investing in a device.
Limitations
Some factors can reduce the
accuracy of a pulse oximeter reading, including:
- changes in the
pulse
- carbon
monoxide poisoning, which may not produce an alert in a pulse oximeter
- bilirubin
levels
- lipids in blood
plasma
- interference
from external light or color, including nail polish
- having cold
hands or poor circulation
People who use pulse oximeters to
monitor oxygen saturation should not rely on the oximeter as a substitute for
subjective experience.
People experiencing difficulty
breathing, shortness of breath, dizziness, or other signs of possible oxygen
deprivation should seek medical attention.
To get the most accurate reading
on a pulse oximeter, there are a few simple steps, according to the World
Health Organization:
Position the probe
correctly. Depending on the device, this will usually be on the finger,
toe, or earlobe. Make sure it is well-fitted, and not being forced on: for
example, try the second toe rather than the big toe. If the probe is too loose
or too tight, it may allow extra light in, which will impact the reading.
Make sure you're sitting still. Shaking
or shivering will affect the reading, and may make it seem much lower than it
actually is.
Remove any nail polish. If
you're wearing coloured nail polish, this might affect the reading. Finger
tattoos or henna dye can also affect the reading: in this case, choose a
different finger, toe, or earlobe. Cold fingers or toes can also cause false
readings.
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