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Pulse Oximeters Overestimate Oxygen Saturation in Some Racial, Ethnic Groups

Were Black patients and those from certain ethnic groups denied more-advanced COVID-19 care because pulse oximetry overestimated their oxygen saturation? A new study suggests that appears to be the case. One result was lower hospitalization rates among patients who likely really needed it, according to the authors. Here is more information.

BALTIMORE – Early in the COVID-19 pandemic, pulse oximeters flew off of pharmacy shelves as public health officials emphasized the importance of knowing when oxygenation levels fell too low in patients infected with SARS-CoV-2.

What they didn’t say, however, was that oxygen saturation might be overestimated in some racial and ethnic groups.

A new study in JAMA Internal Medicine suggests that even the equipment used in healthcare centers didn’t give consistent readings, which raises the question of how racial and ethnic biases affected pulse oximetry readings among COVID-19 patients. Researchers from Johns Hopkins University School of Medicine also put forth concerns that those biases might have led to unrecognized or delayed recognition of eligibility for oxygen threshold–specific therapy.

Their retrospective cohort study involved clinical data on 7,126 patients with COVID-19 from 5 referral centers and community hospitals in the Johns Hopkins Health System. The patients self-identified as Asian, 5.2%; Black, 39.3%; Hispanic, 17.7%; or White, 37.8.

The study team analyzed 1,216 patients with oxygen saturation levels that were concurrently measured by pulse oximetry and arterial blood gas and determined that pulse oximetry tended to overestimate arterial oxygen saturation among Asian, Black, and Hispanic patients compared with white patients.

“Separately, among 6,673 patients with pulse oximetry measurements and available covariate data, predicted overestimation of arterial oxygen saturation levels by pulse oximetry among 1,903 patients was associated with a systematic failure to identify Black and Hispanic patients who were qualified to receive COVID-19 therapy and a statistically significant delay in recognizing the guideline-recommended threshold for initiation of therapy,” the authors write.

Researchers advise that their study results point to an overestimation of arterial oxygen saturation levels by pulse oximetry “in patients of racial and ethnic minority groups with COVID-19 and contributes to unrecognized or delayed recognition of eligibility to receive COVID-19 therapies”.

Results indicate that occult hypoxemia occurred in 19 Asian (30.2%), 136 Black (28.5%), and 64 non-Black Hispanic (29.8%) patients compared with 79 white patients (17.2%).

“Compared with White patients, SpO₂ overestimated SaO₂ by an average of 1.7% among Asian (95% CI, 0.5%-3.0%), 1.2% among Black (95% CI, 0.6%-1.9%), and 1.1% among non-Black Hispanic patients (95% CI, 0.3%-1.9%),” researchers write. “Separately, among 1,903 patients with predicted SaO₂ levels of 94% or less before an SpO₂ level of 94% or less or oxygen treatment initiation, compared with white patients, Black patients had a 29% lower hazard (hazard ratio, 0.71; 95% CI, 0.63-0.80), and non-Black Hispanic patients had a 23% lower hazard (hazard ratio, 0.77; 95% CI, 0.66-0.89) of treatment eligibility recognition.”

The study notes that 451 patients (23.7%) never had their treatment eligibility recognized, most of whom (247 [54.8%]) were Black. Even among the remaining 1,452 (76.3%) who eventually had recognition of treatment eligibility, Black patients had a median delay of 1.0 hour (95% CI, 0.23-1.9 hours; P = .01) longer than white patients.

No significant median difference in delay between individuals of other racial and ethnic minority groups and white patients was documented, however.

“the results of this cohort study suggest that racial and ethnic biases in pulse oximetry accuracy were associated with greater occult hypoxemia in Asian, Black, and non-Black Hispanic patients with COVID-19, which was associated with significantly delayed or unrecognized eligibility for COVID-19 therapies among Black and Hispanic patients,” the authors conclude. “This disparity may contribute to worse outcomes among Black and Hispanic patients with COVID-19.”

Background information points out that modern pulse oximeters provide a noninvasive estimate of arterial blood oxygen saturation levels based on the relative absorbance of 2 wavelengths of light and the pulsatile flow of arterial blood (SpO₂). Past research has reported overestimation of SpO₂ compared with SaO₂ among individuals with skin of darker pigmentation compared with individuals with lighter pigmentation.

With COVID-19, according to the study, pulse oximetry has been used to guide triage and therapy with recommendations for hospitalization and therapy based on SpO₂ thresholds.