Could the ear replace the fingertip for oxygen monitoring?

Millions of people were introduced to fingertip pulse oximeters during the Covid-19 pandemic. The small devices, which measure blood oxygen levels, are now widely available from some online retailers for less than £20.

But researchers have raised concerns about the accuracy of the traditional oximeter for people with darker skin tones, due to the technology it uses to generate a reading.

Pulse oximeters work by sending light waves through a patient's skin to estimate the level of oxygen in the blood, but it has been found that the light can behave differently depending on skin tone.

A study at University Hospitals Birmingham is now researching a new device designed to tackle the problem and hopes to find the solution inside the ear.

For Carlos Lee, from Birmingham, taking part in the clinical study was about more than testing a new piece of medical equipment.

"The study interested me because it's a very meaningful one.

"As an Asian man I wanted to contribute to a study that would feature more diverse skin tones", he said.

Lee was one of 29 volunteers taking part in the research to find a new type of oxygen monitor, which is being developed by healthcare technology company, EarSwitch.

Research had raised concerns that monitors could overestimate oxygen levels in people with darker skin pigmentation, particularly when oxygen levels were already low.

"We've known for some time that the monitors or probes that we use to measure oxygen in patients can be inaccurate at times in patients who have darker or different [skin] pigments," said Dr Dhruv Parekh, a Consultant in Critical Care and Respiratory Medicine.

That did not mean fingertip oximeters were considered unsafe in normal clinical use, as doctors and nurses had generally used them alongside other observations and tests, rather than relying on a single reading alone.

But the limitations had become particularly important when people were monitoring themselves at home.

During the Covid-19 pandemic, for example, patients had increasingly used pulse oximeters without a clinician beside them.

"What recent studies have shown, is when you're unwell, it may show that in people with darker [skin] pigments are being falsely reassured that their oxygen levels are better than they are", Parekh said.

He added: "We need to ensure that when we are showing whether oximeter's work in people, that they work across the board, not just in white Caucasian people, but across all different [skin] pigments and backgrounds and ethnicities."

As a result, researchers started to investigate if oxygen levels could be measured in a different way.

Researchers began looking into whether measuring oxygen from somewhere else on the body could improve the result.

A monitor developed by Earswitch founder, Dr Nick Gompertz, shone light into the external ear canal rather than through the end of a finger.

The thinking was relatively straightforward - unlike the skin on a fingertip, the inside of the ear canal was typically non-pigmented across races.

"The advantage of the ear is inside is the same colour for everybody and also it's much closer to the core central blood supply for everyone, whatever[their] skin colour", Gompertz said.

He added: "During Covid, it became very clear that pulse oximeters were not working adequately for people with brown or black skin and there were higher death rates for that group of people.

"There seemed to be a problem with pulse oximeters, and I felt that this needed to be addressed."

As part of the testing process, volunteers were deliberately given slightly lower blood oxygen levels, before researchers took blood samples from an artery and analysed them using highly accurate laboratory equipment.

"Whenever you design a new pulse oximeter, you have to show that it works," said Professor Tom Clutton-Brock, who works in Anaesthesia and Intensive Care Medicine at the University of Birmingham.

"We compare the pulse oximeter reading with measurements taken directly from arterial blood. That allows us to calibrate the device and show that it works to an acceptable standard."

The study was also designed to meet new international testing requirements, which called for at least 24 volunteers and 480 data points.

Researchers said those standards were important because pulse oximeters need to work reliably across a wide range of people, rather than producing accurate readings only for a small group of patients.

Dr. Giovannie Jean-Louis helped connect Black and Brown participants to the study through the app she co-founded, PROBr.

She said the issue went beyond this one device.

"What we find is that everyone can get the same treatment, but they may not be able to get the same outcome, which means that everyone's quality of life can differ if they're not represented accurately," she said.

The point was not simply about having a diverse group of volunteers for the sake of it.

"Everyone has something that is different from the next person. Being able to account for that when it comes to health is something that will help someone get better treatment, improve their overall health and [have] better outcomes," Jean-Louis added.

The ear monitor was not necessarily intended to replace fingertip oximeters in every setting.

"I think we will continue to use conventional pulse oximetry in the majority of patients, certainly during anaesthesia intensive care, where we are looking for potentially big and dangerous changes," Clutton‑Brock said.

"However, it's a very important lesson that we've learned, that we should not assume that because it works in one group of people, it will always work in another.

If the research showed the ear based device could provide more precise readings across different skin tones, it could eventually have a wider role in healthcare.

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