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What is a Finger Pulse Oximeter?

By Emma Lloyd
Updated May 17, 2024
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A finger pulse oximeter is a small device which measures the amount of oxygen present in a patient’s blood. This is an indirect method of measuring blood oxygen levels, as opposed to a direct method such as testing a blood sample. The fingertip pulse oximeter device is worn on the tip of the finger, and uses light of particular wavelengths to measure oxygen saturation in the blood.

These devices are commonly used in hospitals, particularly in intensive care units, operating rooms, surgery recovery wards, and emergency medicine departments. All of these are places where patients may have unstable blood oxygenation. Because low blood oxygen levels are harmful and may indicate a serious problem, the use of a finger pulse oximeter is standard in many medical situations. The device provides important information which assesses whether a patient needs supplemental oxygen, or monitors the efficacy of supplemental oxygen a patient is already receiving.

Finger pulse oximeters measure the amount of oxygen present in the blood which is circulating in the fingertips. The device does this using red and infrared light to measure oxygen saturation. These types of light can measure the amount of oxygen present in blood because hemoglobin absorbs different amounts of the light depending on whether or not it is oxygenated. Hemoglobin is the component of blood which transports oxygen; this protein binds to oxygen molecules in the lungs, and then transports the oxygen around the body as blood circulates through the vascular system.

The red and infrared light rays are absorbed by hemoglobin, and the fingertip device uses the absorption measurements to calculate the ratio of red and infrared light absorption. Because this ratio depends on whether hemoglobin is carrying oxygen or not, it can be used to calculate the ratio of oxygenated to deoxygenated hemoglobin. The device is so sensitive it can ignore any signals which are sent by tissues in the fingertip, as well as non-organic substances such as nail polish. Only the light absorption of hemoglobin is measured. The measurements are taken in time with the heartbeat of the wearer, which helps improve the accuracy of the hemoglobin ratio.

Many types of finger pulse oximeter measure the wearer’s heart rate in addition to their oxygen saturation. The measurements are displayed on a small readout panel. When the patient is in hospital, the device may also be connected to a medical monitor, allowing staff to monitor the patient even when not in the room. Portable oximeters which can be used at home are also available, as well as modified devices such as a digital finger pulse oximeter, which is easier to calibrate and use.

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Discussion Comments
By anon1003974 — On Oct 19, 2020

What is it connected to?

By Phaedrus — On Aug 13, 2014

I credit a finger pulse oximeter with saving my grandpa's life. He was in the hospital for a suspected heart attack, but the tests they ran didn't add up. One would say he was having a heart attack, but another would say it was a circulation problem or COPD complication. A nurse noticed that his finger pulse oximeter had fallen off, and when they reattached it, they realized he was oxygen-deprived. It might have taken a long time to run a different kind of test for that, but the oximeter's results were immediate and accurate.

By AnswerMan — On Aug 12, 2014

I remember when finger pulse oximeters became widely used in hospitals. I had to go to the emergency room after I wrecked my bike as a kid, and the triage nurse immediately attached a spring-loaded clip to one of my fingers. I could see light coming out of the tip. It scared me at first, because my regular doctor never did that.

She explained to me and my mom that it measured how much oxygen I had in my blood and also my pulse rate. It didn't hurt at all, but I was afraid something bad would happen if it got pulled off. The nurse pulled it on and off, and told me nothing would happen. I just needed to keep it on as much as possible.

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