(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 tissues (e.g., 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 pulse 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 physician 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 interchanges 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 main-stem bronchi.

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