Oximetry

(Oxygen Saturation, Oximetry, Ear Oximetry, Pulse Ox, Sp0₂)

Procedure overview

What is pulse oximetry?

Pulse oximetry is a procedure used to measure the oxygen level (or oxygen saturation) in the blood. It is considered to be a noninvasive, painless, general indicator of oxygen delivery to the peripheral tissues (such as the finger, earlobe, or nose).

How does pulse oximetry work?

Oxygen in the air is breathed into the lungs. The oxygen then passes into the blood where the majority of the oxygen attaches to hemoglobin (a protein located inside the red blood cell) for transport in the bloodstream. The oxygenated blood circulates to the tissues.

Pulse oximetry technology utilizes the light absorptive characteristics of hemoglobin and the pulsating nature of blood flow in the arteries to aid in determining the oxygenation status in the body. First, there is a color difference between arterial hemoglobin saturated with oxygen, which is bright red, and venous hemoglobin without oxygen, which is darker.

Second, with each pulsation or heartbeat there is a slight increase in the volume of blood flowing through the arteries. Because of the increase of blood volume, albeit small, there is an associated increase in oxygen-rich hemoglobin. This represents the maximum amount of oxygen-rich hemoglobin pulsating through the blood vessels.

A clip-like device called a probe is placed on a body part, such as a finger or ear lobe, to measure the blood that is still carrying or is saturated with oxygen. The probe houses a light source, a light detector, and a microprocessor, which compares and calculates the differences in the oxygen-rich versus oxygen-poor hemoglobin. One side of the probe has a light source with two different types of light, infrared and red, which are transmitted through the finger to the light detector side of the probe. The oxygen-rich hemoglobin absorbs more of the infrared light and the hemoglobin without oxygen absorbs more of the red light. The microprocessor calculates the differences and converts the information to a digital readout. This information helps the doctor assess the amount of oxygen being carried in the blood and evaluate the need for supplemental oxygen.

Other related procedures that may be used to assess problems of the lungs and respiratory system include bronchoscopy, computed tomography (CT scan) of the chest, chest fluoroscopy, chest X-ray, chest ultrasound, lung biopsy, lung scan, mediastinoscopy, peak flow measurement, positron emission tomography (PET) scan, pleural biopsy, pulmonary angiography, pulmonary function tests, and thoracentesis. Please see these procedures for additional information.

Anatomy of the respiratory system

The respiratory system is made up of the organs involved in the exchange of gases, and consists of the:

• Nose

• Pharynx

• Larynx

• Trachea

• Bronchi

• Lungs

The upper respiratory tract includes the:

• Nose

• Nasal cavity

• Ethmoidal air cells

• Frontal sinuses

• Maxillary sinus

• Larynx

• Trachea

The lower respiratory tract includes the lungs, bronchi, and alveoli.

What are the functions of the lungs?

The lungs take in oxygen, which cells need to live and carry out their normal functions. The lungs also get rid of carbon dioxide, a waste product of the body's cells.

The lungs are a pair of cone-shaped organs made up of spongy, pinkish-gray tissue. They take up most of the space in the chest, or the thorax (the part of the body between the base of the neck and diaphragm).

The lungs are enveloped in a membrane called the pleura.

The lungs are separated from each other by the mediastinum, an area that contains the following:

• The heart and its large vessels

• Trachea (windpipe)

• Esophagus

• Thymus

• Lymph nodes

The right lung has three sections called lobes. The left lung has two lobes. When you breathe, the air enters the body through the nose or the mouth. It then travels down the throat through the larynx (voice box) and trachea (windpipe) and goes into the lungs through tubes called mainstem bronchi.

One mainstem bronchus leads to the right lung and one to the left lung. In the lungs, the mainstem bronchi divide into smaller bronchi and then into even smaller tubes called bronchioles. Bronchioles end in tiny air sacs called alveoli.

Reasons for the procedure

Pulse oximetry may be performed to assess the adequacy of oxygen levels (or oxygen saturation) in the blood in a variety of circumstances such as surgery, other procedures involving sedation (for example, bronchoscopy), adjustment of supplemental oxygen as needed, effectiveness of lung medications, and patient tolerance to increased activity levels. Other reasons may include, but are not limited to, the following:

• Mechanical ventilation. Use of a ventilator to support breathing.

• Sleep apnea. Periods of cessation of breathing during sleep.

• Medical conditions, such as heart attack, congestive heart failure, chronic obstructive pulmonary disease (COPD), anemia, lung cancer, asthma, or pneumonia

There may be other reasons for your doctor to recommend pulse oximetry.

Risks of the procedure

Pulse oximetry is a quick, noninvasive method of measuring oxygen saturation in the blood. Risks associated with pulse oximetry are minimal and rare.

Prolonged application of the probe may cause tissue breakdown at the application site. Skin irritation may result from the adhesive used in adhesive-containing probes.

Use of pulse oximetry in cases of smoke or carbon monoxide inhalation is not helpful because oximetry cannot distinguish between normal oxygen saturation in the hemoglobin and the carboxyhemoglobin saturation of hemoglobin that occurs with inhalation of smoke or carbon dioxide.

There may be other risks depending upon your specific medical condition. Be sure to discuss any concerns with your physician prior to the procedure.

Certain factors or conditions may interfere with the results of the test. These include, but are not limited to, the following:

• Decreased blood flow to the peripheral vessels

• Light shining directly on the oximetry probe

• Movement of the area to which the probe is attached

• Severe anemia (decreased red blood cells)

• Extreme warmth or coolness of the area to which the probe is attached

• Excessive sweating of the area to which the probe is attached 

• Recent injection of contrast dye

• Smoking tobacco

Before the procedure

• Your doctor will explain the procedure to you and offer you the opportunity to ask any questions that you might have about the procedure.

• If a finger probe is to be used, you may be asked to remove fingernail polish.

• Based on your medical condition, your doctor may request other specific preparation.

During the procedure

Pulse oximetry may be performed on an outpatient basis or as part of your stay in a hospital. Procedures may vary depending on your condition and your doctor's practices.

Generally, pulse oximetry follows this process:

1. A clip-like device called a probe (functions like a clothespin but does not pinch) will be placed on your finger or earlobe. Alternatively, an adhesive probe may be placed on your forehead or finger.

2. The probe may be left on for continuous monitoring or only to obtain a single reading.

3. Unless you are to have continuous monitoring, the probe will be removed after the test.

After the procedure

You may resume your usual diet and activities unless your doctor advises you differently.

Generally, there is no special care following pulse oximetry. However, your doctor may give you additional or alternate instructions after the procedure, depending on your particular situation.

Online resources

The content provided here is for informational purposes only, and was not designed to diagnose or treat a health problem or disease, or replace the professional medical advice you receive from your doctor. Please consult your health care provider with any questions or concerns you may have regarding your condition.

This page contains links to other websites with information about this procedure and related health conditions. We hope you find these sites helpful, but please remember we do not control or endorse the information presented on these websites, nor do these sites endorse the information contained here.

American Cancer Society

American Lung Association

National Cancer Institute (NCI)

National Heart, Lung, and Blood Institute (NHLBI)

National Institutes of Health (NIH)

National Library of Medicine