Pandemic revives controversy over racial disparity in pulse oximetry

The pandemic has sparked an unprecedented use of the pulse oximeter device to make exigent medical decisions about COVID-19—and along with it, a renewed concern about the widely used device's accuracy in estimating oxygen levels in people with darker skin pigmentation.

This performance discrepancy has been recognized in the literature for over 30 years^[], yet it has not been corrected, prompting assertions of racial disparity in oxygen monitoring and calls for pulse oximetry reforms that have reached the FDA.

Recent studies have raised concerns that inaccurate pulse oximeter readings potentially put Black, Asian, and Hispanic patients with COVID-19 at risk of delayed treatment and worse outcomes. The FDA is reviewing the data and its recommendations, and plans for a public meeting in late 2022.^[][]

The ongoing accuracy issue

Pulse oximeters use light beams to estimate oxygen saturation of the blood and the pulse rate through the fingertip.

As discussed in a JAMA Internal Medicine editorial, this has meant that Black, Asian, and Hispanic individuals are more likely to experience occult hypoxemia. (Occult hypoxemia refers to a substantial arterial hypoxemia (SaO2) detected on arterial blood gas but not picked up by simultaneous pulse oximetry (SpO2).^[]

The editorial’s author, Valerie S.M. Valbuena, MD, MSc, cited two key studies on the topic. In one retrospective analysis, researchers found higher rates of occult hypoxemia in Asian, Black, and Hispanic patients compared with those of Whites. Because the pulse oximeter failed to pick up low blood oxygen levels in these patients, it resulted in either delayed or unrecognized eligibility for COVID-19 treatment with remdesivir or steroids.

In the other cited study, researchers found a higher risk of hospital mortality, increased lactate levels, and high sequential organ failure assessment scores—in addition to higher rates of occult hypoxemia—among Asians, Hispanics, and Blacks.

Results from a study published in the New England Journal of Medicine in 2021 indicated that in two large cohorts, Black patients exhibited about three times the frequency of occult hypoxemia compared with that of White patients.^[]

“Given the widespread use of pulse oximetry for medical decision-making, these findings have some major implications, especially during the current coronavirus disease (COVID-19) pandemic,” the authors wrote.

Flaws in pulse-oximeter design can be dire in ICU settings. A study published in 2022 in JAMA Internal Medicine found that Black, Asian, and Hispanic patients received less supplemental oxygen than white patients at the same average hemoglobin-oxygen saturation.^[]

“In this cohort study, Asian, Black, and Hispanic patients received less supplemental oxygen than White patients, and this was associated with differences in pulse oximeter performance, which may contribute to known race and ethnicity–based disparities in care,” the Harvard Medical School authors wrote. “Our findings present a unique and compelling opportunity to improve equity through device reengineering and by reevaluating how data are interpreted.”

Before a technological solution is implemented, some experts recommend that physicians adjust their interpretation of pulse oximeter readings. In a study published in Respiratory Care in 2022, University of Pennsylvania researchers found that measurement error in pulse oximeter readings most often happens with Black patients. Because of the wide variability of measurement error, clinicians should aim for pulse ox readings between 94% and 98%.^[]

FDA to review evidence and recommendations

Due to renewed scrutiny, the FDA is monitoring the situation and issued the following statement on its website:

"Because of ongoing concerns that these products may be less accurate in individuals with darker skin pigmentations, the FDA is planning to convene a public meeting of the Medical Devices Advisory Committee later this year to discuss the available evidence about the accuracy of pulse oximeters, recommendations for patients and healthcare providers, the amount and type of data that should be provided by manufacturers to assess pulse oximeter accuracy, and to guide other regulatory actions as needed."

In the meantime, the FDA advises that patients with such conditions as COVID-19 who are using at-home pulse oximetry should take into account all other signs and symptoms of their disease and report concerns to their healthcare practitioner.

Dr. Valbuena stated that even though differences in pulse-oximetry readings can seem most important with thresholds such as that for extracorporeal membrane oxygenation in Black patients, physicians should nonetheless keep occult hypoxemia in mind when treating patients with darker skin tones. She stressed that children are particularly vulnerable to even mild occult hypoxemia.

Wider implications

Except for the issue’s newfound attention, the problem with pulse oximeters is entrenched. Dr. Valbuena believes that this issue represents “historical neglect of racial and ethnic [minority] groups and diminished concern for their health outcomes.”

The devices are designed with White users in mind, and this is in part an economic decision, as per Dr. Valbuena. Regarding COVID-19, she felt the decreased detection of hypoxemia further exacerbated “multilevel injustices” and “persistent disparities” among minorities.

“Although an easy bedside adjustment for the measurement disparity is an attractive idea, there is no proven approach because of the noise and variable bias of the currently available devices," Dr. Valbuena said.

Finally, she explained that there are improved pulse oximeters that utilize increased wavelengths of light for those with darker skin, but they are not in widespread use.