As Covid embeds itself in our communities and we pivot to a home isolation model, pulse oximeters play an increasingly important role. But there’s a serious problem with this handy medical device, explains Charlotte Muru-Lanning.

The Covid-19 pandemic has introduced us to many new terms: epidemiology, genomic sequencing, fomite transmission and, of course, assiduous. Perhaps one of the newest terms to enter the mainstream vocabulary is pulse oximeter.

The pulse oximeter is a small, potentially life-saving device often given to Covid-19 patients isolating at home, which clips onto a person’s finger to estimate the amount of oxygen in their blood. 

But last week, the UK’s health secretary launched a review into racial bias in medical equipment after research found pulse oximeters worked less effectively for patients with darker skin, sometimes overstating the amount of oxygen in their blood. Health secretary Sajid Javid said because of this issue, people of colour may have been less likely to attain necessary hospital care and oxygen machines than white people, and this may have contributed to unnecessary deaths during the pandemic. 

Evidence from the UK in 2020 suggests that people of colour have been at greater risk from Covid-19 than white people there. In New Zealand, a study earlier this year found that Māori were two-and-a-half times more likely to be hospitalised with Covid-19 than Pākehā, and Pasifika three times more likely.

In Aotearoa, Covid-19 cases are increasingly isolating at home rather than in quarantine facilities, with currently more than a thousand doing so, and the device has become ever-more important in self-managing symptoms. This shift in approach to isolation, coupled with the fact the outbreak has been dominated by Māori and Pasifika, means the pulse oximeter findings are important to consider, says Victoria University public health researcher Dr Clive Aspin (Ngāti Maru, Ngāti Whanaunga and Ngāti Tamaterā). 

The pulse oximeter problem is an example of something that occurs in the health sector time after time, he says. “Everyone gets treated as if we’re all the same, when in actual fact we’re all different.” He compares it to other examples of medical biases within our system, like the long-standing lack of provision for HPV self-testing that Māori experts have repetitively called for. “If people had access to self-testing for HPV, we wouldn’t get the high rates of cancer or cervical cancer among Māori women,” he says. Earlier this year, it was announced that HPV self-testing would be rolled out nationwide in 2023. 

Andrew Taberner, professor with the Auckland Bioengineering Institute at University of Auckland, explains that pulse oximeters work by using two slightly different colours of light that are invisible to the human eye, so “people’s skin is going to react in different ways to the light that is passing”.

“Clearly the evidence is showing that this isn’t fully accounting for the variations in skin colour that occur in the population,” he says.

This could be an unintended outcome of the way these technologies are developed, explains Taberner. “Unfortunately, in a lot of cases, when devices get to the medical device company who are trying to commercialise the technology, they focus on what is potentially their biggest market,” he says. That can lead to anomalies where devices don’t work as well on people outside that intended market demographic – in this case those with darker skin. 

Taberner doesn’t believe this is a case of deliberate racism on the part of medical device manufacturers, but says it could be an example of systemic bias, and he suspects it could be an issue with other medical devices that use light to read skin too. It highlights the need for designers of such tools to ensure they’re tested “across as broad a population as possible in age, skin colour, ethnicity and gender, to ensure that we don’t overlook these sorts of possibilities”, he says.

Skin colour isn’t the only factor that changes the accuracy of a pulse oximeter, says University of Auckland senior lecturer in nursing Kim Ward, with cold fingers, light, movement, anaemia and nail polish all potentially interfering with the reading of the devices. 

While this might sound alarming, “it is a tool in a gamut of different assessment tools that we use”, she says, including monitoring respiratory rates and symptoms like changing skin colour and confusion. “And actually, people’s gut instinct to call for help is usually pretty on the money, so if you are wondering about calling for help, then you probably should.”

Ward’s advice to those isolating with Covid-19 is to do as nurses do in hospitals, which is to keep a note over time of your pulse oximetry rate along with your respiratory rate (the number of breaths you take in a minute). “When we’re doing pulses and blood pressures and respiratory rates in hospital, we chart them down, and you can see them make up a picture.

“Oximetry is certainly going to help you understand how you are doing. But it’s not the only thing. And you can make a decision to access health care by paying attention to how you feel as much as by paying attention to oximeter readings.”

Taberner agrees that monitoring trends over time is a useful way to mitigate potential inaccurate oximeter readings. “It’s the trending that would probably reveal health issues of emerging concern more than the absolute number itself,” he says. 

Aspin reiterates that the readings from pulse oximeters are just one indicator of unwellness, “so people shouldn’t rely just on a little instrument to decide whether or not to see a health professional”.

This underscores the importance of thorough check-ups from health professionals for people isolating at home, says Aspin. Last week, after reports emerged of people not receiving adequate clinical care while self-isolating, health commissioner Morag McDowell told The Spinoff she had written to the Ministry of Health to say the matter needed “urgent attention”. Yesterday, the government announced around $1.5 billion in funding for a new “care in the community” model for Covid-19 patients, including ongoing clinical monitoring.

Because of the potential racial bias ingrained in pulse oximeters, health professionals checking in on self-isolating Covid patients should be giving appropriate weight to other indicators of wellness, says Aspin.

They should also consider that some people have an innate distrust  of medical science, often influenced by past negative interactions with health professionals, and may struggle to rely on a piece of medical technology, he adds. For similar reasons, says Aspin, people might in fact over-rely on the technology. “We need to bear in mind that some people may find it more difficult engaging with health professionals.”

To counter this, it’s important Covid patients get clear and culturally sound information about how to use the devices properly and are encouraged to make early contact with health professionals, he says. “We need people who are acceptable to community members to go there and provide the answers and the information.”