Critical care
even slight overestimations of oxygen saturation in this range could put patients at risk of severe organ damage or death, neither study appears to have impacted either device design or clinical practice. Certainly, Michael Sjoding, an assistant professor of pulmonary and critical care and hospital medicine at the University of Michigan Medical School in Ann Arbor, had no idea that there was such a glaring flaw in one of his most important diagnostic tools. Then the first surge of Covid brought him an influx of breathless patients from nearby Detroit. As 78% of Detroit’s population identify as black or African American, compared with 7% in Ann Arbor, this radically altered the hospital’s patient demographic, revealing some uncomfortable truths about Sjoding’s practice in the process. “Honestly, when we were caring for these patients, we saw this phenomenon happening,” recalls Sjoding. “The pulse oximeter was reading a normal value, and then, just by chance, we had a confirmatory arterial blood gas [ABG] test drawn, and it was way off. We had no idea what to make of it.”
Like most of his peers around the world, Sjoding had been operating under the assumption that pulse oximeters were as accurate as numerous clinical studies suggested. Prior to Covid this caused few, if any, issues, because the population of those clinical studies looked a lot more like the residents of Ann Arbor than Detroit. Suddenly forced to apply expertise honed for a quite homogenous patient group to a much more diverse one, however, Sjoding and his colleagues became increasingly aware of a mismatch between their expectations and the reality on the wards. “I think because we were caring for so many more black patients than was typical, this was a thing we started noticing, which we weren’t really keen to,” he says. Nonetheless, at first, Sjoding and his “puzzled” colleagues wondered whether this was a Covid-specific issue. If not for the unlikely intervention of medical anthropologist Amy Moran-Thomas and the literary magazine Boston Review, their interest in it may well have waned as their patient demographic normalised. In the course of her research, Moran- Thomas, a professor at MIT, unearthed the articles cited above, along with a curious tendency for medical practitioners and device designers to deny that their findings mattered in practice. As she notes in her August 2020 article ‘How a Popular Medical Device Encodes Racial Bias’, “Most oximeters on the market today were initially calibrated primarily for light skin, and they still often reproduce subtle errors for non- white people.”
Sjoding saw the piece. “She dug out this old research describing these potential disparities and discrepancies and postulated that it might be happening in the Covid pandemic,” he explains. “We were like: ‘This is happening in the Covid pandemic – we’ve seen it with our own eyes’.”
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Investigating the problem To prove it, Sjoding and his colleagues quickly launched a real-world study comparing pulse oximeter and ABG readings from patients hospitalised at the University of Michigan in 2020 as well as others across 189 hospitals in 2014–15. “We wanted to show that it’s still an important problem and probably remains very underappreciated,” he says.
The team found that pulse oximeters can provide misleading results in more than one in ten black patients. Specifically, black patients in the study had nearly three times (11.7%) the frequency of occult hypoxaemia (arterial oxygen saturation of less than 88% and a pulse oximetry (SpO2) reading of 92–96%) as white patients (3.6%).
In the context of a pandemic that has disproportionately affected ethnic minorities in Western countries, as well as the growing support for the Black Lives Matter movement, Sjoding’s study, published as a research letter in the New England Journal of Medicine, did what its predecessors couldn’t: it drew attention to the problem. For Olamide Dada, who was working for the NHS Race and Health Observatory at the time, the findings were not exactly a surprise. “Just observing the impact that Covid-19 was having on ethnic minority groups, in my head it was, ‘Why haven’t people put two and two together and considered this as a potential contributing factor?’” she says.
Sjoding is similarly bemused that his work should have been so heralded. “Our publication, which has been quite well-received and has made a big impact, in some respects isn't new,” he sighs. “The knowledge has been around for a while, so why wasn't this corrected 20 years ago? And, moreover, here we are, practising physicians, and we're not aware of this knowledge, or of the past studies demonstrating the bias could exist. It was not disseminated in any meaningful way.” That looks like it might be changing. In March 2021, Dada, a newly qualified doctor and the founder of the UK charity Melanin Medics, authored the NHS Race and Health Observatory report “Pulse oximetry and racial bias: Recommendations for national healthcare, regulatory and research bodies”. A month earlier, the FDA issued a public warning about the devices’ limitations, although it did not explicitly mention racial disparities in their accuracy. Elsewhere, Sjoding has seen US universities update their medical curriculums to reflect issues with pulse oximeters in non-white patients, and numerous specialist societies and medical bodies have released statements and recommendations. The Anesthesia Patient Safety Foundation (APSF), for one, now advises that “clinicians should not make patient care decisions such as hospital or intensive care unit discharge on the basis of a single SpO2 value”. But there are a lot of doctors out there. In the UK, at least, Dada believes much more needs to be done to reach them. Once again, she’s concerned that the wider
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www.practical-patient-care.com
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