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This blogpost partakes from a blogpost published in Boston Review. The link appears at the end. The article is written by AMY MORAN-THOMAS
On December 17, 2020, the New England Journal of Medicine published a research letter, “Racial Bias in Pulse Oximetry Measurement,” prompted by some of the issues explored in this essay.
Fact 1. Pulse Oximeter became a household name during COVID pandemic in Pakistan and everywhere else. Here, the price increased from 650 rupees to 6500 rupees and the item disappeared from the market. It is not a new phenomenon in Pakistan. The businesses are quick to take advantage of any situation. This part besides, a lot of people depended on the Pulse Oximeter to determine if they needed hospitalization or not.
Fact 2. Pulmonologists recommend that oxygen inhalation may be required if oxygen saturation drops below 92%. Between 92% to 95% it is of concern, but if it goes between 88 and 92%, it is considered an emergency. Oxygen saturation must be given in this condition.
Fact 3. The Pulse Oximeter measures oxygen saturation in the blood by shining two lights – one infrared, one red – through our finger and sensing how much passed through on the other side. Oxygen-saturated hemoglobin absorbs more infrared light and also allows more red light to pass through than its deoxygenated counterpart. Adjusting for certain technicalities using our pulse, the device reads out the color of our blood several times a second. To see our blood, the light must pass through our skin and this is where the racial bias comes in.
Fact 4. Pulse Oximeter and other such imaging devices are calibrated for white/light skins. The scanning light is adjusted accordingly. When the same device is used on darker skins – Blacks, Browns – the results may be twisted. Studies have shown that due to skin pigmentation, the oxygen saturation reading as shown on the Pulse Oximeter may be higher than what it actually is. This difference may be in critical range and may have serious clinical implications.
Fact 5. This is another facet of racial bias. This fact has been known about scanning devices for quite some time, but no serious effort has been done to make the correction. Rather, the difference has been usually brushed aside, calling it ‘non-critical’.
Fact 6. We, in Pakistan, have a range of skin colors – from fair to very dark – and this fact impacts our population also. We may start discussing it as it is also relevant here, not from racism point of view but due to its clinical implications.
Some revealing information mentioned by Amy Moran-Thomas in her essay is given below.[Quote]
In 2005 a team of physicians studied oximetry’s racial bias in critical detail. The group often works at the famous mountaintop Hypoxia Lab, founded at the University of California, San Francisco (UCSF) by John Severinghaus, inventor of blood gas analysis, who did foundational work in medical devices for anesthesiology. “In our eighteen years of testing pulse oximeter accuracy,” the team noted in their article, “the majority of subjects have been light skinned. . . . Most pulse oximeters have probably been calibrated using light-skinned individuals, with the assumption that skin pigment does not matter.”
But after hearing about a range of “unacceptable errors in pulse oximetry” among Black wearers, the UCSF study was “specifically designed to determine whether errors at low [arterial oxygen saturation] correlate with skin color.” Since errors don’t tend to show up at healthy oxygen levels, a special protocol is necessary to check accuracy at lower oxygen, which better simulates an actual health crisis. The doctors collected readings with a range of people using several pulse ox models, then checked their readings against a different kind of test based on arterial blood gas, the “gold standard” test for oxygen levels. (The latter measure is more invasive, requiring blood from an artery, which is why the pulse ox is often used as a proxy in hospitals.)
Crosschecking these two measures over 1,067 data points, the team found a clear pattern of errors. For nonwhite people the machines mostly tended to overestimate saturation levels by several points. The study only included participants who identified as Black or white, but the authors noted that degrees of errors have also been observed among Latinx, Indigenous, and many other nonwhite people. The team’s follow-up study, published in 2007, focused on safety errors for people with “intermediate” skin tones and included a larger group of women. This more detailed data again found a clear pattern: pulse ox “bias was generally the greatest in dark-skinned subjects, intermediate for intermediate skin tones, and least for lightly pigmented individuals.” Racial errors grew significant at lower oxygen levels, starting around 90 and growing widest in the 70s.
Indeed, while the oximeter is a key tool for some patients in deciding when to go to the hospital, it’s also what they use at the hospital. Clinical guidance about giving oxygen tends to be loosely keyed to a certain threshold of oxygen saturation; protocols recommend particular interventions at 88, 90, and 92 percent, for example. Racial errors in these higher saturation ranges tend to be narrower disparities of one to four percentage points, but they still can mislead if they go undetected. In particular situations, another study notes, errors of that margin “may severely affect the treatment decisions in borderline cases.”[Unquote]
It is apparently an insignificant point that the devices like Pulse Oximeter are calibrated using white skin. But it has serious implications when it comes to making treatment decisions in critical conditions. In the US, it has additional issues due to entrenched and imbedded racial biases. In Pakistan, it is not about racism, it is about treating correctly.