Pulse oximeters beam light through the blood, and skin pigmentation may affect how light is absorbed, with darker skin colour absorbing less light.
The pulse oximeter uses a cold light source that shines a light through the fingertip, making the tip appear to be red. By analyzing the light from the light source that passes through the finger, the device is able to determine the percentage of oxygen in the red blood cell. 22 Feb 2021
A device designed to spot early signs of dangerous falls in oxygen levels in Covid patients works less well in those with darker skin, experts are warning.NHS England and medicines regulator, the MHRA, say pulse oximeters may sometimes overestimate oxygen levels.The devices beam light through the blood, and skin pigmentation may affect how light is absorbed, they say.Anyone with concerns is advised to look for changes over time rather than relying on a single reading.NHS England is issuing upda credit: https://www.bbc.com/news/health-58032842
APSF Statement on Pulse Oximetry and Skin Tone
Jeffrey Feldman, MD; Meghan Lane-Fall, MD, MSHP
On December 17, 2020, Sjoding et al. published a retrospective analysis of pulse oximetry (SpO2) data from two patient cohorts indicating that in some patients, occult hypoxemia was not detected when compared to paired oxyhemoglobin saturation measured by laboratory co-oximetry (SaO2).1 Occult hypoxemia was defined as an SaO2 of < 90% when the paired SpO2 measurements were 92% or greater. The authors compared sub-groups from the cohorts self-identifying as Black and White, and found that the incidence of occult hypoxemia was three times greater in Black patients (11.7%) compared with White patients (3.6%). As the authors noted, these findings, if correct, have important patient safety implications since patient triage based upon pulse oximeter measurements could fail to lead to appropriate escalation of care. As a retrospective, uncontrolled study without objective measurements of skin tone, the analysis performed by Sjoding et al. has important limitations. Nevertheless, it is important to verify these findings to understand if there is the potential for pulse oximeter measurements to mislead clinicians, especially in patients with dark skin tones.
The preponderance of evidence supports the conclusion that there is a measurement bias in pulse oximeter measurements due to skin tone such that pulse oximeter measurements may overestimate the actual oxyhemoglobin saturation in patients with dark skin tones. Laboratory data obtained under controlled conditions does not indicate that the magnitude of the bias is significant enough to influence clinical decision making until the saturation is less than 80%. Clinical performance is likely to be different from that obtained in the laboratory, and it is clear that many factors will influence the accuracy of pulse oximetry in addition to skin tone. Therefore, clinicians should not make patient care decisions such as hospital or intensive care unit discharge on the basis of a single SpO2 value.
Despite the known limitations of the pulse oximeter, APSF believes that patients are safer with continued use of pulse oximetry to estimate arterial oxygenation. It is potentially more harmful if the known bias in measurement related to skin tone resulted in a lack of confidence in pulse oximetry as a monitoring tool for patients with dark skin tones.
The findings by Sjoding et al. require verification but present at least two opportunities to improve clinical care and outcomes. First, there is an opportunity for manufacturers, regulators, and clinicians to work together to ensure that technology is developed and tested to document clinical performance in demographically and clinically diverse populations. The FDA’s requirement for inclusion of “darkly pigmented subjects” in device development warrants reconsideration. Requirements for objective measurement of skin tone should be specified. More importantly, including 15% darkly pigmented subjects in the study group may reduce the average measurement bias in that population, but not necessarily result in ideal performance for the individual patient. Closer scrutiny to minimizing measurement bias in subjects with dark skin tones is warranted, including reconsideration of the 15% threshold. Second, this is an opportunity to examine more closely how pulse oximetry is used in the clinical setting and to heighten awareness of the factors that can lead to inaccurate measurements. Like any monitoring device, the measurements obtained by a pulse oximeter are estimates of the actual physiologic condition and can be erroneous. Factors other than skin tone known to affect the accuracy of pulse oximetry include perfusion, dyshemoglobinemias, anemia, brand of oximeter, and motion. Sound clinical decision making depends upon a complete assessment of the patient, not a reliance on a single monitored parameter.
APSF supports the renewed attention to the accuracy of the pulse oximeter, which has rightly revolutionized medical care and augmented patient safety. We call on clinicians, manufacturers, and regulators to work together to ensure that this device offers equitable benefits to all the patients we serve.
Jeffery Feldman is an anesthesiologist at Children’s Hospital of Philadelphia and clinical professor of Anesthesiology in the Perelman School of Medicine University of Pennsylvania.
Meghan Lane-Fall is vice chair of Inclusion, Diversity, and Equity and David E. Longnecker Associate Professor of Anesthesiology and Critical Care & Associate Professor of Epidemiology in the Perelman School of Medicine, University of Pennsylvania.