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Pulse Oximetry

Pulse Oximetry

Alternate Names

  • oxygen saturation
  • O2 saturation


Pulse oximetry is an indirect way to measure the level of oxygen in the blood of the arteries.

Who is a candidate for the test?

Pulse oximetry is commonly used to monitor the level of oxygen in a person's blood during heavy sedation or anesthesia. It can often detect problems before they are noticed by the person or by a healthcare professional. This test is also used for a person who is on a ventilator (an artificial breathing machine).
The SaO2 helps the health care professional determine whether the person needs a change to the level of oxygen therapy being delivered. Pulse oximetry can also be used in other clinical settings. These may include pulmonary rehabilitation programs, stress testing, and sleep labs. It can be used to check the body's response to different medications.
A healthcare professional may also order this test at an office visit. This may be done in the case of a child or adult with asthma who is having trouble breathing.

How is the test performed?

A small clip with a sensor is attached to the person's finger, earlobe, or toe. The sensor is connected to the pulse oximeter machine by a small cable. The sensor gives off a light signal that passes through the skin. The sensor measures the amount of light the tissue absorbs, which is directly related to the oxygen saturation of hemoglobin. This information is transmitted to the pulse oximeter. A reading is given in a percentage form.

What is involved in preparation for the test?

If a person has on fingernail polish, this should be removed. The polish can cause falsely low readings.

What do the test results mean?

A reading lower than 90% may be due to any factor which affects blood, hemoglobin, and oxygen circulation in the body. These may include:
  • excessive bleeding
  • lung problems, such as pneumonia
  • cigarette smoking
  • blood vessel problems
  • long-standing respiratory disease, or chronic obstructive pulmonary disease. Below normal SaO2 readings may be the norm for individuals with this condition.
If any of these complications are present, the healthcare professional may order additional tests to better assess oxygen saturation.


Mosby's Medical, Nursing and Allied Health Dictionary, 5th Ed.

Clinical Reference for Critical Care Nursing, 3rd Ed.

The Patient's Guide to Medical Tests, Yale University, 1997

Mosby's diagnostic and Laboratory Test Reference, 4th Ed. 1999

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