Unreliable pulse oximeter readings in darker skinned patients may delay COVID treatment


By Geir O'Rourke

2 Jun 2022

Darker skinned patients may be missing out on necessary treatment for COVID-19 because pulse oximeters are still not calibrated to adjust for differences in skin tone, researchers say.

The warning follows a study of more than 7,000 patients in the United States, which found the devices overestimated oxygen levels by an average of 1.7% in Asian patients and 1.2% in African Americans.

As a result, pulse oximetry failed to identify hypoxaemia in 3.7% of samples from the two groups, based on readings collected during routine clinical care at five hospitals within the Johns Hopkins Health System.

Occult hypoxaemia occurred in some 1.7% of samples from white patients, the researchers found.

All up, some 30% of Asian patients, 29% of African American patients and 17% of white patients had at least one occult hypoxic reading during their hospital stay.

This was defined as SaO2<88% with concurrent SpO2 of 92%-96% from an arterial oxygen saturation measurement taken 10 minutes later with a blood gas analyser.

The oxygen measurement issues were associated with “systematic misclassification of patient oxygenation status based on racial or ethnic self-identification,” they wrote in JAMA Internal Medicine.

“In addition, we found a systematic failure to identify Black and Hispanic patients who were likely qualified to receive COVID-19 therapy and a statistically significant delay in recognising the guideline recommended threshold for initiation of therapy among Black patients compared with White patients.”

The findings may go some way towards explaining the disproportionate virus mortality rate among African Americans, who the US Centres for Disease Control and Prevention had found were 1.7 times more likely to die from COVID-19 than white patients, the researchers added.

Oximeter readings on white patients were far from perfect either, even given allowances for the 10 minutes between paired SpO2 and SaO2 measurements.

Nevertheless, the errors were still more pronounced among racial and ethnic minority groups, the researchers wrote.

“This study’s results suggest that for critical treatment decisions that rely on arterial oxygen saturation, use of pulse oximetry may be inadequate and produce opportunities for undertreatment and overtreatment irrespective of the patient’s race or ethnicity,” they wrote.

“This mirrors inaccuracies in capillary blood glucose levels reported among patients with critical illness.”

It followed a letter in the MJA last month raising concerns about similar issues with oximeter readings on darker skinned patients locally.

The authors, from the TGA and the Central Australian Retrieval Service in Alice Springs, argued this should influence decisions around hospital transfer of home-care patients with COVID-19.

“Clinicians and services should arguably have lower thresholds for hospital review and admission of patients with dark skin (including Indigenous Australians and those of African and South Asian descent) with borderline oxygen saturations, while balancing risks of increased ABG and invasive treatment rates,” they wrote.

They noted that the TGA did not regulate devices sold directly to consumers for non-medical purposes, making it difficult to provide advice for those using pulse oximeters for general wellness or sport.

“Contemporary evidence demonstrates that dark skin is a risk factor for hypoxia being undetected by pulse oximetry,” the authors wrote.

“Clinicians should adjust treatments and guidelines accordingly and consider audits of devices used in their institutions.”

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