Pulse oximeter readings unreliable to assess COVID-19 pneumonia severity across ethnicities

Pulse oximeter measurements of blood oxygen levels appear to be unreliable to assess the severity of COVID-19 pneumonia across different ethnicities, according to new data published in the European Respiratory Journal.

Pulse oximeters provided a false reading of nearly 7% higher among mixed-ethnic individuals with COVID-19 compared with just over 3% among white individuals with COVID-19. Researchers also reported falsely high readings in patients with both Black and Asian ethnicity.

“This data builds on what we know, which is that patients with darker skin have less accurate oxygen measurements using the pulse oximeters,” Andrew Fogarty, MD, clinical associate professor and reader in clinical epidemiology and faculty of medicine and health sciences at the University of Nottingham Medical School, U.K., said in a related press release. “Any error of measurement of oxygen levels will make assessing the severity of COVID-19 infection more difficult and may delay delivery of timely medical care. We are now exploring the impact of this on clinical outcomes to see if it may have led to any issues in escalating treatment intensity for our patients.

Fogarty and colleagues analyzed electronic data for 2,997 patients admitted to Nottingham University Hospitals NHS Trust from February 2020 to September 2021. All patients had suspected or confirmed SARS-CoV-2 infection. Mean pulse oximetry and blood gas measurement differences were stratified by white, mixed, Asian or Black ethnicity. These measurements were also stratified by oxygen saturation level.

The primary outcome was pulse oximetry measurements with a paired blood gas measurement within a 30-minute time frame.

Compared with arterial blood gas, the researchers reported variation in the mean oxygen saturation difference measured by pulse oximetry (P = .02). The highest differential was observed among mixed-ethnic individuals (6.9%; 95% CI, –21.9 to 35.8) and the lowest differential among white individuals (3.2%; 95% CI, –22.8 to 29.1). Black individuals (5.4%; 95% CI, –25.9 to 36.8) and Asian individuals (5.1%; 95% CI, –23.8 to 34) had intermediate differentials, according to the study.

Pulse oximetry overestimated oxygen saturations across all ethnicities when arterial blood gas oximetry measurements were less than 90% and underestimated these when saturations were more than 95%

“These mean differences were particularly marked in the clinically important range when the arterial blood gas demonstrated a true oxygen saturation of 85% to 89%; individuals with a Black ethnicity had a mean pulse oximetry reading that was 3.9% higher (95% CI, –8 to 15.9), those with an Asian ethnicity 5.8% higher (95% CI, –1.6 to –13.2) and individuals with a white ethnicity 2.4% [higher] (95% CI, –14.2 to 19), when compared to arterial blood gas oxygenation,” the researchers wrote.

Compared with white individuals, Black (1.8%; 95% CI, 0.2-3.4; P = .04), Asian (1.9%; 95% CI, 0.6-3.2; P = .005) and mixed-ethnic (3.2%; 95% CI, –0.1 to 6.6; P = .06) individuals also had higher pulse oximetry readings for oxygen saturation in a mixed-effects linear model. In a final mixed-effects model, pulse oximetry overestimated arterial oxygen saturation by a mean 1.4% in patients with Black, Asian or mixed ethnicity compared with white individuals after adjusting for sex, age and arterial blood oxygen level (P = .003).

“Our analysis extends the concerns about pulse oximeters giving a falsely high reading in patients with Black ethnicity to those from Asia as well. This is important, as high levels of skin pigmentation are associated with the ethnic groups who have a poorer outcome from COVID-19 ... and hence would require the most accurate oxygen measurements available to titrate supplemental oxygen and deliver timely treatment,” the researchers wrote in the study. “Although these data cannot quantify the impact of these measurement errors of pulse oximetry on clinical care, our experience is that any delay in appreciating the severity of COVID-19 pneumonitis is likely to be detrimental to patient care, especially now that new therapeutic options are becoming available.”

Reference:

• Pulse oximeter measurements of blood oxygen levels are unreliable in assessing severity of COVID-19 pneumonia across different ethnic groups. Published Jan. 27, 2022. Accessed Jan. 27, 2022.