Health Letter, August 2022
By Michael Carome, M.D.
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Pulse oximeters are noninvasive medical devices that measure the oxygen level (specifically, oxygen saturation) in the arterial blood of patients by shining specific wavelengths of light through tissue — most commonly the fingernail bed. The oxygen saturation readings, which often are referred to as the “fifth vital sign,” from these medical devices play a crucial role in the assessment and monitoring of patients who have conditions that adversely affect breathing or the function of the lungs or heart or who are undergoing procedures requiring sedation or general anesthesia.
For most healthy people, the blood oxygen saturation measured by a pulse oximeter normally ranges between 95% and 100% while resting at sea level.
Since the early 1980s, the Food and Drug Administration (FDA) has cleared more than 300 pulse oximeters for marketing in the U.S. Importantly, research published in 1991 — more than 30 years ago — revealed that pulse oximeters overestimated arterial blood oxygen saturation levels in Blacks. Subsequent research, including well-designed studies published in 2005 and 2007, demonstrated that individuals with darker skin in general were more likely than individuals with lighter skin to have inaccurate pulse oximeter readings that overestimated blood oxygen saturation levels, particularly at lower levels.
Such racial and ethnic discrepancies in the performance of pulse oximeters during the care of potentially seriously ill patients predictably could lead to clinically important low oxygen levels (called hypoxemia) going undetected more frequently in Asian, Black and Hispanic patients, which in turn could contribute to inadequate treatment for the low oxygen levels and worse health outcomes in such patients compared with White patients.
Two studies recently published in the Journal of the American Medical Association (JAMA) Internal Medicine provided troubling new evidence of the racial and ethnic discrepancies in the performance of pulse oximeters. The first study, which was published online on May 31, 2022, examined whether there were systematic racial and ethnic biases in pulse oximetry data among patients with COVID-19 and whether there was an association between such biases and unrecognized or delayed recognition of eligibility for COVID-19 therapy that was based on specific arterial oxygen saturation levels.
For one part of the study, the study researchers retrospectively analyzed clinical data from 1,216 COVID-19 patients treated within the Johns Hopkins Health System from March 2020 to November 2021 who had concurrent measurements of arterial oxygen saturation levels by pulse oximetry and by direct testing of arterial blood samples, which is the most accurate way to measure blood oxygen levels. Of these patients, 63 (5%) self-identified as Asian, 478 (39%) as Black, 215 (18%) as Hispanic and 460 (38%) as White. The researchers found that hypoxemia went undetected by pulse oximeter readings in 19 Asian patients (30%), 136 Black patients (29%), and 64 non-Black Hispanic patients (30%), whereas only 79 cases of hypoxemia in White patients (17%) went undetected. In addition, compared with readings in White patients, pulse oximeter readings overestimated arterial oxygen saturation levels by an average of 1.7% among Asian patients, 1.2% among Black patients and 1.1% among non-Black Hispanic patients.
In a separate analysis, the researchers found that the predicted overestimation of arterial oxygen saturation levels by pulse oximeter readings among 1,903 patients was associated with a systematic failure to identify Black and Hispanic patients who were qualified to receive COVID-19 therapy under existing treatment guidelines and a statistically significant delay in recognizing the guideline-recommended threshold for initiation of such therapy.
The second recent JAMA Internal Medicine study, which was published online on July 11, 2022, assessed whether there were differences in the use of supplemental oxygen therapy among patients of different races and ethnicities associated with discrepancies in the performance of pulse oximeters. For this study, researchers retrospectively analyzed clinical data from 3,069 intensive care unit patients admitted to Beth Israel Deaconess Medical Center from 2008 to 2019. Of these patients, 83 (3%) were
Asian, 207 (7%) were Black, 112 (4%) were Hispanic and 2,667 (87%) were White based on self-reporting of race and ethnicity. The researchers once again demonstrated that Asian, Black and Hispanic patients had pulse-oximeter readings that overestimated their actual arterial blood oxygen levels to a greater extent than White patients. The researchers also found that Asian, Black and Hispanic patients received less supplemental oxygen therapy than White patients and that this difference was associated with the differences in the performance of pulse oximeters among these racial and ethnic groups.
A note from the JAMA Internal Medicine editors that accompanied the publication of the second study discussed above offered the following succinct commentary:
It is unsurprising that the “fifth vital sign” determines the timing and dosage of appropriate therapies. Yet as [the authors of the July 11, 2022, study] note, [oxygen saturation readings by pulse oximeters are] a particularly troubling contributor to racial and ethnic disparities, as device development and data interpretation are firmly within the control of the health care sector. Devices exist that perform more equitably but have never been widely distributed. Health care systems, including academic centers, are large-scale purchasers of pulse oximeters. If they make a commitment to buy only devices that function across skin tones, manufacturers would respond.
But the real blame for the wide use in the U.S. of pulse oximeters that have inherent racial and ethnic discrepancies in their performance falls squarely on the shoulders of the FDA. On June 21, 2022, the FDA issued the following statement:
The FDA continues to evaluate all available information pertaining to factors that may affect pulse oximeter accuracy and performance. 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 health care 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.
The agency should have taken regulatory action decades ago to ensure that manufacturers only market pulse oximeters that perform equitably across all racial and ethnic groups. The FDA’s dereliction of duty in its regulatory oversight of pulse oximeters has contributed to racial disparities in health care and likely the suffering and deaths of countless Asian, Black and Hispanic patients.