NEJM Journal Watch
Neil H. Winawer, MD, SFHM
And the difference in accuracy might have clinical consequences.
Pulse oximeters estimate the oxygen saturation of blood (SpO2) noninvasively by passing two wavelengths of light through the body and measuring the change in absorbance. This reading can be affected by the amount of melanin in the skin, and recent data from various hospital settings suggest that readings sometimes might differ from the arterial blood gas (ABG)–derived oxygen saturation (SaO2).
In a retrospective study from three U.S. hospitals, researchers paired 128,000 SpO2 measurements with their associated SaO2 readings in 26,000 adult intensive care unit (ICU) or surgical inpatients. After adjusting for potential confounders, self-identified Black patients were significantly more likely to have occult hypoxemia (defined as SaO2 <88% despite normal SpO2 [i.e., ≥92%]) than were white patients (6.2% vs. 3.6%). Self-identified Asian and American Indian patients also had greater risk for occult hypoxemia than did white patients, but differences were not statistically significant, perhaps due to low numbers of minority patients. Occult hypoxemia was associated with higher risk for mortality in both surgical and ICU patients (NEJM JW Gen Med Mar 15 2022 and Crit Care Med 2022; 50:204).
In a study of general medical and surgical inpatients in U.S. Veterans Affairs hospitals, researchers paired pulse oximeter and arterial blood oxygen readings taken minutes apart. Among 30,000 pairs analyzed, occult hypoxemia was significantly more likely in Black than in white patients (19.6% vs. 15.6%, respectively; NEJM JW Gen Med Aug 15 2022 and BMJ 2022; 378:e069775).
Finally, investigators examined data from 3000 patients who received supplemental oxygen in an ICU in Boston. Average SpO2 values were significantly higher for Black (97.6%), Asian (97.3%), and Hispanic (97.2%) patients than for white patients (96.7%). Black patients had lower SaO2 values than did white patients (95% vs. 96%; NEJM JW Gen Med Sep 15 2022 and JAMA Intern Med 2022; 182:849).
Taken together, these studies add to a growing body of evidence that patients with darker skin pigmentation are at risk for delayed recognition of hypoxemia. In some cases, that delay might be clinically significant, leading to further disparities in care. Oximeters that are accurate across a range of skin tones are in development, with the first device recently cleared by the U.S. FDA. Until such devices are adopted widely, clinicians should maintain a low threshold for obtaining ABG-measured SaO2 in patients with darker skin pigmentation and normal SpO2 values when the index of suspicion for hypoxemia is high.
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