Could Pulse Oximeters Be Racist?

Do you know that skin colors can influence the accuracy of pulse oximeters? 

 

Pulse oximeters have become quite useful during this covid-19 pandemic. Some covid-19 patients suddenly develop the condition called “silent hypoxia,” during which they still look and feel comfortable, but their SpO2 is perilously low, which may indicate severe COVID-19-related diseases. SpO2, also known as oxygen saturation, is a measure of the amount of oxygen-carrying hemoglobin in the blood relative to the amount of hemoglobin not carrying oxygen. The body needs there to be a certain level of oxygen in the blood or it will not function as efficiently. It is important to eliminate errors in measurement and makes clinical decision-making easier for doctors and nurses. 

 

 However, both the device itself and the way it is calibrated are characterized by biases that are linked to the person’s skin color. These factors contribute to this apparent racial bias in oximetry measurements although it was no doubt unintended by its inventors. 

 

You might ask why skin color is an issue. Well, that’s because the device works by measuring the time-varying optical signal produced by the interaction of red and infrared light with tissue perfused with blood. How light interacts with the tissue results in photons—- light wave particles, either absorbed or scattered by molecules such as hemoglobin—- red blood cells, melanin, lipids, and water.

 

The team performed a systematic review based on bibliometric analysis—- statistical methods to analyze large numbers of books and articles from scientific databases and evaluate them quantitatively. They use statistics from the results of different brands of oximeters. Using this method, they build a fair portrayal of the current research trends on this topic. These systematic reviews give an all-inclusive bunch of relevant materials to this question. 

 

It turns out sadly but also unsurprisingly that the effects of skin pigment on pulse oximeter performance have been studied for only a relatively small number of pulse oximeter models, and most of them have been calibrated using light-skinned individuals.  

 

Pulse oximeters overestimate the true oxygen saturation of the dark skins, according to a retrospective report by Sjoding et al.1 that was motivated by clinical experiences from early in the epidemic. Because of this error, patients with deeper colors have a roughly three times higher risk of missing a diagnosis of hypoxemia—a disorder marked by low amounts of oxygen in the blood—than white patients. When arterial blood-gas tests for misdiagnosed individuals show oxygen saturation levels of less than 88% (signaling hypoxemia), despite pulse oximeters showing healthy oxygenation of more than 92%, this condition is referred to as occult hypoxemia.

 

Darker-skinned individuals—those who identify as Black, Asian, Hispanic, or a combination of these—are more likely than white individuals to develop occult hypoxemia, according to a number of sizable retrospective studies. In a study of COVID-19 patients, 35% of those who identified as Black had their eligibility for oxygen treatment postponed, or even missed it entirely, compared to just 20% of the white patients documented2. In a different study, white and black participants who had equal arterial blood-gas readings received less therapeutic oxygen. A more thorough examination revealed that patients with occult hypoxemia are more likely to experience organ dysfunction and in-hospital mortality and that Black people in this category experience the worst organ dysfunction.

 

Cabanas, A. M., Fuentes-Guajardo, M., Latorre, K., León, D., & Martín-Escudero, P. (2022). Skin Pigmentation Influence on Pulse Oximetry Accuracy: A Systematic Review and Bibliometric Analysis. Sensors (Basel, Switzerland), 22(9). https://doi.org/10.3390/s22093402