Pulse oximeters and why they are used

Pulse oximetry is a well-established technique used in healthcare to take a non-invasive measurement of the blood-oxygen level of a patient. This measurement can help with the early detection of signs of deterioration. The value produced is just one part of the range of measurements that clinicians use to decide on the most appropriate treatment. The changes in the oxygen saturation value may be more important than just the number reported.

Factors which can affect the accuracy of pulse oximeters

Typically, these devices work by shining a light into the skin and measuring how this is absorbed by the blood to estimate how much oxygen is present. Because of this, it is possible that patients with lighter skin may have small differences in the result reported when compared to those with darker skin. This is just one factor that can alter the result produced.

Other well-known factors include:

low perfusion
movement
nail polish
henna dye
tattoos
probe mispositioning
ambient lighting hitting the sensor

The relative change in a patient’s reading may be of greater significance to clinical management than the absolute value. The MHRA is not aware of any incidents where skin colour has had an adverse effect on the use of pulse oximeters when providing effective clinical care.

Home use of pulse oximeters

The MHRA does not recommend that members of the public use oximeters at home unless they have been advised to do so by a qualified clinician, have been shown how to take an accurate measurement, and they are providing results for clinical review. General information on medical devices for users and patients is available from the MHRA. Advice from the NHS on pulse oximeters can be found here.

The NHS COVID Oximetry @home and COVID Virtual Wards services are aimed at high-risk patients with coronavirus (COVID-19). They are supported by teams of healthcare professionals who provide the necessary instructions on good practice in taking measurements and advice on passing results for clinical interpretation.

Regulation of pulse oximeters

All medical devices on the UK market must meet stringent requirements for safety and performance under the UK Medical Device Regulations 2002 (SI 2002 No 618, as amended). Pulse oximeters intended for clinical use are regulated as medical devices and should display a valid CE, CE UKNI or UKCA mark.

The MHRA does not approve medical devices directly. In the case of pulse oximeters and other higher risk medical devices, the manufacturer shows their compliance with the regulations with third-party approval by a designated approved body. Although not mandatory, market approval is expected to include compliance with the relevant technical product standard BS EN ISO 80601-2-61:2019 (Medical Electrical Equipment. Particular requirements for basic safety and performance of pulse oximeter equipment).

See information on how medical devices are regulated.

Manufacturers are required to report serious incidents involving their medical devices. Investigation of these reported incidents is an important aspect of the MHRA’s medical device safety monitoring system.

Advice for clinicians interpreting pulse oximetry readings in Sp02 sensors and standalone fingertip devices

The reading may vary between different devices and patients. To meet the accuracy requirements of the applicable technical standard, the root-mean-square difference between the oximeter and the true value must be below 4% across the range of 70-100% SpO2. Below 70% SpO2 the accuracy falls. Although pulse oximetry will not give a precise value of oxygen saturation, it is useful for following trends. It does not measure carbon dioxide (CO2) levels.

To get the best performance and precision, consider the following points that affect the calculation of SpO2.

Use an appropriate device and ensure it fits securely.

Too tight causes constriction; too loose lets light in. Do not pull or stretch the cable and beware of motion artefacts when transporting patients.

Nail coatings

Where possible remove nail polish, check for false nails or consider an alternative site.

Poor peripheral blood circulation

This may reduce the arterial pulsation, making it difficult to pick up a signal. Situations can include hypovolaemia; cold; cardiac failure; arrhythmias; peripheral vascular disease; and the position of a non-invasive blood pressure cuff.

Darker skin pigmentation

This may cause an overestimate of SpO2 saturations, so consider relative changes in an individual patient’s readings as well as the numerical result.

Dyes, henna or tattoo ink

The use of some dyes, such as methylene blue (as used in surgery), henna or tattoo ink may affect the absorption of light and the results produced.

Other factors

clean and maintain devices according to the manufacturer’s recommendations
replace damaged or faulty devices
in an MRI environment only use probes designated MR CONDITIONAL or MR SAFE

Reporting problems

We encourage healthcare professionals to report any suspected or actual adverse incidents involving these devices, as well as shortcomings with device performance or instructions for use. Report through your healthcare institution’s local incident reporting system and/or your national incident reporting authority as appropriate: England, Scotland, Northern Ireland, Wales.

Members of the public in any part of the UK can report through the Yellow Card scheme.

The use and regulation of pulse oximeters (information for healthcare professionals)