However, pulse oximeters don’t work as well for people with darker skin. There is risk of “hidden hypoxemia” where the device says that the oxygen levels are fine but the actual saturations of the patients are dangerously low. Recent Medical studies to have quantified this bias and the consequences of overestimated oxygen levels. For example, Hispanic and black patients with the coronavirus were about a quarter less likely to be recognized as eligible for treatment. Getting an accurate oxygen reading can literally be a matter of life and death.
Despite the recent increased attention to this topic, racial bias in pulse oximeters is nothing new; in fact, it was embedded in the very development of this technology. A closer look at the history of oximeters reveals how placing a premium on market convenience over fairness allows bias to creep into medicine.
The first oximeters were developed for military use, not medical use. During World War II, fighter pilots passed out at high altitudes, so American and German scientists developed oximeters. for their respective air forces. These early devices hooked into pilots’ ears and alerted them when they needed supplemental oxygen.
Hewlett-Packard (HP) went on to develop the ear oximeter for health care in the 1960s and 1970s, with a remarkably liberal and transparent focus on fairness. In the October 1976 issue of your magazine., for example, HP acknowledged how oxygen readings were affected by “skin and blood pigments, and skin surface characteristics,” before describing how they designed their own device so that oxygen readings accurate, regardless of skin color. The HP device was also tested on 248 black patients and could be personally calibrated with a patient’s blood. Yale professor of medicine Meir Kryger, who tested some of the early HP oximeter models as a pulmonology fellow at the University of Colorado, said the company “really got serious about the pigment business at a time when no one did.”
But HP’s oximeter was huge and cumbersome to use, as well as expensive. It’s cost $13,000 in 1970. Therefore, the device was relegated to a few select research laboratories and was understood to be clinically impractical. HP eventually discontinued its ear oximeter and stopped manufacturing medical devices altogether.
However, in 1974, two Japanese companies took the next step in oximetry when Nihon Kohden and Minolta independently invented devices that measure oxygen levels through the beating of a patient’s arteries. The first “pulse” oximeters had arrived, with both companies applying for patents within a month of each other.
Although electrical engineer Takuo Aoyagi won this patent race for Nihon Kohden, the company did not pursue the device because it was just a side project for them. “Aoyagi made a prototype,” Katsuyuki Miyasaka, an anesthesiologist at St. Luke’s International University and a close colleague of Aoyagi’s, explained in an interview, “but there wasn’t much interest in developing it further.”
Minolta went ahead and, in 1977, released the OXIMET-Met-1471, probably the first fingertip oximeter ever developed. With fiber optic cables sending light to and from the clip, the device was technologically advanced but, like HP’s, not clinically practical. It was extremely sensitive to motion, too heavy to be used on patients, and often overestimated oxygen levels in very sick patients, although it was otherwise fairly accurate. The device was not tested on any people of color because, in a country as ethnically homogeneous as Japan“Skin color may not be a problem,” Miyasaka said.
After being frustrated by the lack of success at home (only 200 devices were never sold), Minolta attempted to market its pulse oximeter in the United States, distributing the device for evaluation by several American hospitals. William New, a former HP electrical engineer and Stanford University anesthesiologist, soon learned about the Minolta device and saw its shortcomings, but also its great potential.
New and two other colleagues founded the Nellcor company and, in 1981, released their own pulse oximeter, the N-100. The device was designed to be clinically practical. With LED lighting and a flexible paper-like sensor, the Nellcor oximeter was disposable and virtually unaffected by movement. One of the most popular features of the device was how it changed its tone based on the patient’s oxygen saturation, making it easier to recognize low oxygen levels.
Nellcor’s timing was extremely fortuitous. LEDs became increasingly available in the early 1980s, just as a series of malpractice lawsuits were filed against anesthesiologists who were monitoring oxygen levels during surgery. What The CEO of Nihon Kohden recently wrote, Nellcor “ridden the wave of technological innovation and market changes right now.” The N-100 dominated the market, “selling like hotcakes,” according to Miyasaka. In fact, a Canadian anesthesiologist described how “Nellcor” and “pulse oximeter” became synonyms.
But Nellcor’s device was not equitable. The company was so focused on developing an easy-to-use, clinically practical pulse oximeter that it neglected the racial bias integrated your devices. In 1987, Kryger compared the N-100 to the HP oximeter and found that Nellcor’s device was not as accurate or responsive as HP’s.
Racial bias, of course, is not unique to Nellcor: most pulse oximeters have been calibrated on fair-skinned individuals only. And it’s not enough to say that the medical community didn’t know any better: They long ago understood how yellow skin color due to jaundice, blue due to sepsis, and natural non-white skin color could lead to “skin pigmentation effect”, Miyasaka. he said, “but they thought that, statistically or practically, you can ignore it.” The supposed harmlessness of biased design continues to justify its existence.
HP’s device in the early 1970s was the exception that proves the rule. Although his oximeter was clunky and clinically impractical, it was a model of inclusion because HP engineers made elimination of bias a priority. Racial bias in pulse oximeters, or any medical device, is never inevitable. Fairness requires intentionality.