Pulse oximeter
What is a fingertip pulse oximeter?
An easy-to-use device to help you monitor the oxygen level in your blood. It is non-invasive (no needle) and takes just a few seconds to work.
Why is it important to monitor my oxygen levels?
When your oxygen level is low, you may feel tired or have shortness of breath, but you may not feel different at all. This can be dangerous. You should keep track of your oxygen level using a fingertip oxygen meter until you are feeling better. If your oxygen level drops, you should get medical help right away.
How do I use my fingertip oximeter?
- Measure your oxygen level twice per day, in the morning and at night (or more often if instructed by your health care provider).
- Make sure there are batteries inside and turn the device on.
- Put your index finger (the finger next to your thumb) into the oxygen meter with your fingernail facing up. If the screen does not show a number, try another finger (not your thumb). Oxygen meters may not work on cold or wet fingers, or if your finger has nail polish.
- .Wait for the screen to show a number.
How do I read the numbers on the screen?
Your oxygen meter shows two numbers. The oxygen level is labeled SpO2. The other number is your heart rate. For most people, a normal oxygen level is 95% or higher and a normal heart rate is generally below 100. Your oxygen levels and heart rate can change based on your activity, body position and overall health. Check with your health care provider if you have questions.
How should I clean my oximeter?
Wipe off all surfaces of the oxygen meter using a cloth, paper towel or cotton ball dampened with rubbing alcohol that contains at least 60% isopropyl. Do this after each use and before being used by others.
Can I use an oximeter on a child?
Oxygen meters are not recommended for children younger than 14 years old.
Monitor your child’s symptoms closely and call their health care provider if they look sick or develop a cough that worsens or difficulty breathing.
Should I inform my health care provider of my measured oxygen levels?
It is important to keep your health care provider informed about your health and your oxygen levels. Call or email your provider as directed.
Oxygen Level Guidance
90% or less This oxygen level is very concerning and may indicate a severe medical problem. Call or go to your nearest emergency room immediately. You may need an urgent x-ray or heart test.
91% to 94% This oxygen level is concerning and may indicate a medical problem. Call your health care provider immediately.
Go to a nearby urgent care facility.
95% to 100% This oxygen level is normal. Walk around for two minutes and measure your oxygen level again. If your oxygen level falls below 95%, follow the instructions above.
How does a pulse oximeter work?
The pulse oximeter consists of a probe containing LEDs and a photodetector. The LEDs emit light at fixed, selected wavelengths. The photodetector measures the quantity of light transmitted through a selected vascular bed such as a fingertip or earlobe. Pulse oximetry uses the Beer-Lambert law of light absorption. This law describes how light is absorbed when it passes through a clear solvent, such as plasma, that contains a solute that absorbs light at a specific wavelength, such as hemoglobin.[4] The absorption spectra of oxygenated and reduced hemoglobin differ. For this reason, arterial blood appears red, while venous blood appears blue. However, because living tissue absorbs light, it is difficult to determine the ratio of saturation of hemoglobin in the body. The oximeter probe overcomes this difficulty by emitting pulses of light, one red and one infrared. A detector is placed opposite the lights on the other side of the tissue. The diodes switch on and off in rapid sequence, and the detector measures the differences. The measurements feed into an algorithm in a microprocessor where the oxyhemoglobin saturation is calculated and eventually displayed to the user.
Pulse oximeters risk of inaccuracy.
Pulse oximeters have limitations and a risk of inaccuracy under certain circumstances. In many cases, the level of inaccuracy may be small and not clinically meaningful; however, there is a risk that an inaccurate measurement may result in unrecognized low oxygen saturation levels. Therefore, it is important to understand the limitations of pulse oximetry and how accuracy is calculated and interpreted.
FDA-cleared prescription pulse oximeters are required to have a minimum average (mean) accuracy that is demonstrated by desaturation studies done on healthy patients. This testing compares the pulse oximeter saturation readings to arterial blood gas saturation readings for values between 70-100%. The typical accuracy (reported as Accuracy Root Mean Square or Arms) of recently FDA-cleared pulse oximeters is within 2 to 3% of arterial blood gas values. This generally means that during testing, about 66% of SpO2 values were within 2 or 3% of blood gas values and about 95% of SpO2 values were within 4 to 6% of blood gas values, respectively.
However, real-world accuracy may differ from accuracy in the lab setting. While reported accuracy is an average of all patients in the test sample, there are individual variations among patients. The SpO2 reading should always be considered an estimate of oxygen saturation. For example, if an FDA-cleared pulse oximeter reads 90%, then the true oxygen saturation in the blood is generally between 86-94%. Pulse oximeter accuracy is highest at saturations of 90-100%, intermediate at 80-90%, and lowest below 80%. Due to accuracy limitations at the individual level, SpO2 provides more utility for trends over time instead of absolute thresholds. Additionally, the FDA only reviews the accuracy of prescription use oximeters, not OTC oximeters meant for general wellness or sporting/aviation purposes.
Many patient factors may also affect the accuracy of the measurement. The most current scientific evidence shows that there are some accuracy differences in pulse oximeters between dark and light skin pigmentation; this difference is typically small at saturations above 80% and greater when saturations are less than 80%. In the recently published correspondence by Sjoding, et. al.External Link Disclaimer, the authors reported that Black patients had nearly three times the frequency of occult hypoxemia (low oxygen levels in the blood) as detected by blood gas measurements but not detected by pulse oximetry, when compared to White patients. It is important to note that this retrospective study had some limitations. It relied on previously collected health record data from hospital inpatient stays and could not statistically correct for all potentially important confounding factors. However, the FDA agrees that these findings highlight a need to further evaluate and understand the association between skin pigmentation and oximeter accuracy.
All premarket submissions for prescription use oximeters are reviewed by the FDA to ensure that clinical study samples are demographically representative of the U.S. population, as recommended by FDA guidance, Pulse Oximeters – Premarket Notification Submissions [510(k)s]: Guidance for Industry and Food and Drug Administration Staff. As described in this guidance, FDA recommends that every clinical study have participants with a range of skin pigmentations, including at least 2 darkly pigmented participants or 15% of the participant pool, whichever is larger. Although these clinical studies are not statistically powered to detect differences in accuracy between demographic groups, the FDA has continued to review the effects of skin pigmentation on the accuracy of these devices, including data from controlled laboratory studies and data from real world settings.
USA There are two categories of pulse oximeters: prescription use and over the counter (OTC).
Prescription oximeters are reviewed by the FDA, receive 510(k) clearance, and are available only with a prescription. The FDA requires that these pulse oximeters undergo clinical testing to confirm their accuracy. They are most often used in hospitals and doctors’ offices, although they may sometimes be prescribed for home use.
Over-the-counter (OTC) oximeters are sold directly to consumers in stores or online and include smart phone apps developed for the purpose of estimating oxygen saturation. Use of OTC oximeters has increased as a result of the COVID-19 pandemic. These products are sold as either general wellness or sporting/aviation products that are not intended for medical purposes, so they do not undergo FDA review. OTC oximeters are not cleared by the FDA and should not be used for medical purposes.