A pulse oximetry test may clip to a finger to read blood flow.
People with respiratory or cardiovascular conditions, very young infants, and individuals with some infections may benefit from pulse oximetry.
In this article, we look at how pulse oximeters work and what to expect when using one.
Contents of this article:
What is pulse oximetry?
Oxygen is distributed into the blood in red blood cells.
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 hemoglobin proteins in red blood cells. These proteins provide oxygen to the rest of the body.
Pulse oximetry measures the percentage of oxygen in hemoglobin 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.
How pulse oximeters work
Pulse oximeters are clip-on devices that measure oxygen saturation. The device may be attached to a finger, a wrist, a foot, or any other area where the device can read blood flow.
Oxygen saturation can drop for many reasons, including:
- infections, such as pneumonia
- diseases, such as emphysema, lung cancer, and lung infections
- inhaling poisonous chemicals
- heart failure or a history of heart attacks
- allergic reactions
- general anesthesia
- sleep apnea
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.
Who can benefit from pulse oximetry?
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 nighttime oxygen saturation level of someone with suspected sleep apnea 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 newborns
- 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 anesthesia
- indicating dangerous side effects in people taking drugs that affect breathing or oxygen saturation
Pulse oximeters are now widely available to buy, so some people without specific risk factors may use them.
Some companies now market pulse oximeters to parents of young infants. These devices promise peace of mind to parents concerned about sudden infant death syndrome (SIDS) and sleeping accidents, but no research supports the claim that they can prevent SIDS or accidents.
What to expect from pulse oximetry
Pulse oximetry devices are noninvasive 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 of pulse oximetry
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.