Pulse oximeters overestimate oxygen saturation in darker skin pigments

Key takeaways:

• Pulse oximeter inaccuracy due to darker skin tones was found in 30 out of 44 studies.
• Some studies showed a relationship between reduced oxygen saturation and overestimation bias.

Among individuals with darker skin tones, pulse oximeters often overestimated their oxygen saturation levels, according to a systematic review published in British Journal of Anaesthesia.

“This systematic review highlights the need for clinicians to take account of a person’s skin tone as part of the clinical decision-making process when using pulse oximeters to estimate oxygen levels,” Eugene Healy, PhD, professor of dermatology at the University of Southampton and honorary consultant in University Hospital Southampton NHS Foundation Trust, said in a University of Plymouth press release.

After searching through various databases from inception to March 2023, Healy and colleagues found and reviewed 44 studies (n = 222,644; one study did not report number of patients), including 733,722 paired pulse oximetry-derived oxygen saturation (SpO₂)-true arterial oxygen saturation (SaO₂) measures, to find out how skin pigmentation impacts pulse oximeter accuracy.

As Healio previously reported, the Anesthesiology and Respiratory Therapy Devices Panel of the FDA’s Medical Devices Advisory Committee found that pulse oximeters show clear “disparate performance” for darker skin pigmentation.

When collecting patient data, ethnicity was reported more frequently than skin tone (11 studies; n = 2,353). Within the total cohort, non-white ethnicity or a non-light skin tone was found in 68,930 patients (31%).

Notably, children made up a small number of the total population (n = 6,121), and over half of the included studies (64%) had a high risk of bias as determined by the QUADAS-2 tool.

Researchers observed three study design types in this analysis: prospective clinical (18 studies; n = 2,170; 35.9% non-white/darker skin tone), retrospective clinical (18 studies; n = 220,036; 30.9% non-white/darker skin tone) and healthy volunteer (8 studies; n = 438; 58.7% non-white/darker skin tone).

Since the search for these studies went as far back as 1976, researchers noted that some of the pulse oximeters used are obsolete in today’s world, and this should be considered when interpreting these results.

In the healthy volunteer studies, pulse oximeters frequently overestimated SaO₂ in patients with dark skin tones (four studies). Underestimation of SaO₂ and increased errors with use of pulse oximetry in this patient population were also each noted in one study.

During this assessment, researchers also found a relationship between reduced SaO₂ and overestimation bias, which means that patients with darker skin tones and hypoxemia may not receive necessary care due to an inaccurate pulse oximeter reading.

Pulse oximeter inaccuracy due to skin tone was not found in half of the assessed prospective clinical studies, whereas all but one of the remaining studies showed that pulse oximeter use in patients with dark skin tones overestimated SaO₂. The one study that did not yield this result instead found decreased bias among patients with darker skin tones and was the only study to demonstrate this finding.

Significantly more patients with a dark skin tone experienced suboptimal pulse oximeter function compared with patients with light or intermediate skin tone (32% vs. 11% vs. 11%) in one of the studies that did not find inaccuracy due to skin tone.

In the last study design cohort, researchers found pulse oximetry inaccuracy attributable to ethnicity in all but one of the retrospective clinical studies. Similar to the above observations, patients with ethnicities linked to darker skin tones experienced overestimation of SaO₂ with pulse oximeter use. This finding ended up being reported in 30 studies (68%).

Researchers could not conduct meta-analysis due to differences in study design, population, pulse oximeter model and data reported across the included studies.

“As clinicians, we rely on accurate data to make informed clinical decisions,” Daniel Martin, OBE, professor of perioperative and intensive care medicine at the University of Plymouth and consultant at the University Hospitals Plymouth NHS Trust, said in the release. “But during the COVID pandemic, and to some extent since, it was necessary to put thresholds in place which meant that people were only admitted to hospital if their levels fell to a certain point.

“If those levels are being overestimated — so, for example, if a device is telling someone their oxygen saturation is 98% whereas it is in fact significantly lower — it could realistically mean people are missing out on treatments they need,” Martin continued.

Reference:

• Detailed study demonstrates how pulse oximeters significantly overestimate oxygen readings in people with darker skin tones. https://www.plymouth.ac.uk/news/detailed-study-reveals-how-pulse-oximeters-significantly-overestimate-oxygen-readings-in-people-with-darker-skin-tones. Published Feb. 29, 2024. Accessed March 7, 2024.