2025/09/25 by Kelly A. Stockelman, Roger Martin-Pressman, Michael L. Mestek · 1 voice
Biochemistry, Genetics and Molecular Biology · Medicine · #Infrared Thermography in Medicine #Spectroscopy Techniques in Biomedical and Chemical Research #melanin and skin pigmentation
paper · doi:10.1097/01.asm.0001168436.93935.52
openalex publication_date 2025/09/25 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/23
Pulse oximetry is a noninvasive technology that uses sensor-emitted light to estimate blood oxygenation (SpO2) (J Anesth 2003;17:259-66). Long considered a vital sign, pulse oximeters function by emitting red and near-infrared LED light through tissue to measure the light absorbance associated with blood volume increase during the arterial pulse. Factors that impact light absorption, such as melanin, can impact this process (Physiol Meas 2023;44:05TR01; Respir Care 2022;67:1499-7). Recent studies have demonstrated that pulse oximeters overestimate SpO2 in individuals with greater concentrations of melanin, with the degree of this overestimation increasing with increasing melanin levels and with decreasing perfusion (Cureus 2023;15:e46078; Anesth Analg 2024;138:552-61). “For anesthesiologists, it is likely that no monitor has more importance than the pulse oximeter,” says Randall M. Clark, MD, FASA. “Yet despite being in common clinical use for more than 40 years, it is far too easy to take the information it is giving us for granted. For maximum safety and optimal outcomes, every anesthesiology professional must understand the limitations of the technology and how positioning, skin melanin content, and other patient characteristics affect accuracy.” Shanique Brown Kilgallon, MD, pediatric anesthesiologist, explains further that, “Understanding the limitations of our monitors allows us to understand the limitations in our practice. Our goal as anesthesiologists is and forever will be to return the patients we care for to the families who trusted us with them, hopefully better than when they first arrived in the operating room.” Pulse oximetry in clinical practice Melanin is just one of several physiological factors that may contribute to inaccurate pulse oximeter readings (Table). Proper sensor placement and use in accordance with a device's instructions for use mitigate the risk of inaccurate readings as devices are tested and calibrated to light pathlengths of specific tissue sites (Anesth Analg 2007;105:S10-7; J Biomed Opt 2009;14:024046). For example, studies have found that finger sensors placed on ears are shown to provide inaccurate readings by an average of 5% or greater (Thorax 2018;73:A198; Respir Care 2007;52:727-9). However, despite the error associated with inappropriate sensor placement, a recent survey found that 78.6% of nurses and physicians will place a sensor on an ear when a patient's finger does not get a good reading (Medtronic Internal Market Research Survey. March 2024).† Table - Common causes and mechanisms of unreliable SpO2 readings. ©2025 Medtronic. Inaccuracy Causes Intermittent dropouts or inability to read SpO2 Poor perfusion due to a number of causes, e.g., hypovolemia, vasoconstriction, etc. Excessive movement High skin melanin concentration Falsely high Carbon monoxide poisoning Sickle cell anemia with vaso-occlusive crisis (overestimation of FO2Hb and underestimation of SaO2) Venous pulsations Excessive movement Intravenous pigmented dyes Sickle cell anemia without vaso-occlusive crisis Falsely low Inherited forms of abnormal hemoglobin Fingernail polish Sunscreen or pigmented creams Severe anemia (with concomitant hypoxemia) Ambient light Methemoglobinemia Falsely low or high Sulfhemoglobinemia Poor probe positioning Sepsis and septic shock Clinicians should consider the most appropriate sensor type for a given physiological condition. For example, in hypotensive, vasoconstricted patients, ear- or forehead-specific pulse oximeters may be more reliable (Respir Care 2022;67:1499-7). Arterial blood gas measurement remains the definitive measurement of arterial oxygen saturation and should be used if there is any question about the accuracy of plethysmographic oximetry. Clinical research on pulse oximetry technology Although disparate bias in pulse oximetry performance in patients with darker skin tones was first recognized in the literature in 1990, the issue gained notable reemergence of scientific inquiry in 2020, largely due to the COVID-19 pandemic (Chest 1990;97:1420-5; Chest 1990;97:814-9; Physiol Meas 2023;44:05TR01). Over the past 30 years, pulse oximeter manufacturers, regulatory bodies, and independent researchers have undertaken crucial efforts to not only confirm these inaccuracies but also understand the clinical impact of disparate bias in pulse oximetry performance, particularly in challenging clinical conditions such as low perfusion. For example, a 2024 study from a leading hypoxia lab looked at the accuracy of Nellcor™ pulse oximetry in 25, 78, and 43 healthy adults with light, medium, and dark skin pigmentation, respectively, as a function of perfusion index (PI) (Anesth Analg 2024;138:552-61). Similarly, a recent interim analysis of the POSTer-Child study published in the New England Journal of Medicine evaluated the performance of Nellcor™ pulse oximetry in 320 pediatric patients undergoing cardiac catheterization (132 light, 112 medium, 75 with dark pigmentation as determined by individual typology angle) (N Engl J Med 2025;392:1033-4). Both recent studies draw a distinction between light, medium, and dark skin tones in their methodology and subsequent evaluation of device performance. Medtronic has also internally evaluated its Nellcor™ pulse oximeters for performance in darker skin tones and published its findings in a recent white paper. It was found that 85% of subjects had an individual typology angle (ITA) value of < -30°, consistent with the darkest ITA category on a 6-point scale. Research into the role of skin tones will benefit from FDA draft guidance, published in January 2025. The FDA recommends use of the subjective Monk Skin Tone scale and the objective individual typology angle spectrophotometric measurement (asamonitor.pub/4eNPw1O). The draft guidance proposes that at least 25% of study participants fall into each Monk Skin Tone group representing light, medium, and dark skin tones. This is intended to provide objective measurement of skin pigmentation, rather than the substantially less accurate of race as a surrogate for skin tone (Anesth Analg 2024;138:552-61; N Engl J Med 2025;392:1033-4; Respir Care 2022;67:252-7). The recent FDA draft guidance provides additional clarity on recommended methodology. Other key research methodologies include concurrent sampling of SpO2 and SaO2 values and controlling for confounding variables such as optical shunting (J Clin Monit Comput 2023;37:1481-8). Research guidance can also be found in the Open Oximetry Project and the FDA-funded EquiOx study (openoximetry.org/about). Clinicians can visit the Open Oximetry project to find independent evaluation of pulse oximeters (openoximetry.org/oximeters).‡ Though timing is unclear on anticipated publication of the FDA final guidance, Medtronic and other manufacturers have already been incorporating recommendations into validation studies and encouraging industry partners to push for more stringent guidelines during FDA panel discussions. As device manufacturers continue to evolve pulse oximeters, it will be important for clinicians to advocate for adoption of improved technologies once available. Real-world clinical studies will also be critical to understand how pulse oximeters perform outside of the controlled laboratory setting and inform actionable insights for device manufacturers to bring the safest and most reliable technology to the market. However, collecting the necessary pulse oximetry data in the standard of care setting could pose a major challenge. As researchers continue to navigate pulse oximetry in the real-world setting, we encourage clinicians interested in generating real-world evidence to partner with manufacturers through channels such as Medtronic's External Research Program, which supports a global network of investigator-sponsored projects with the goal of improving patient care and clinical outcomes (asamonitor.pub/46CST9B). Internally, Medtronic continues to conduct its own clinical research on pulse oximeters through its Clinical Physiology Laboratory in Denver, Colorado. This lab partners with local organizations to ensure diverse recruitment and uses the Monk Skin Tone scale and objective individual typology angle measurement to ensure accuracy across varying skin pigmentations. Looking to the future This year, investigational Nellcor™ technology was accepted into the FDA's Safer Technologies Program to develop medical devices reasonably expected to improve the safety of currently available options (asamonitor.pub/3GJCqG3). For health care professionals, it is critical to keep clinical best practices top of mind as even small errors in pulse oximeter performance can lead to treatment delays and further health impacts (N Engl J Med 2020;383:2477-8). These include proper device usage according to instructions for use and considering arterial blood gases when other signals indicate SpO2 readings may be overestimated due to medium or dark skin pigmentation. Hospital policymakers can also evaluate research on strategies for mitigating occult hypoxemia rates for applicability to their own populations (Respir Care 2022;67:1499-7). According to Dr. Clark, “The quest for maximum accuracy in pulse oximeters is ultimately an engineering challenge, and fortunately one that device manufacturers are willing and well-equipped to meet.” Dr. Kilgallon shared her hopes that, one day, conversations on skin pigmentation no longer need to happen. “As pulse oximetry evolves to be a better monitor for all patients, it will inevitably help us to be better doctors to all patients and presumably lead to better outcomes.” Medtronic Disclaimers: † Digital survey (n=66) of physicians, nurses, and hospital executives based in U.S., U.K., and Germany. ‡ Performance data are derived from multiple sources, including studies independently conducted in healthy volunteers as part of the Open Oximetry project. Data have not been peer-reviewed and may not accurately represent performance in other settings or in real-world patient populations. The information displayed shall not be construed as an endorsement by Open Oximetry. The Nellcor™ pulse oximetry monitoring system should not be used as the sole basis for diagnosis or therapy and is intended only as an adjunct in patient assessment. Please consult the instructions for use manual for full safety information. ASA Disclaimer: The views and opinions expressed in this article are those of Medtronic, an ASA Corporate Supporter, and do not reflect the official policy or position of ASA. It should not be interpreted as an endorsement by ASA. The article has been reviewed and approved for publication by the ASA Monitor Editorial Board.Kelly A. Stockelman, PhD, Medical Affairs Program Manager, Clinical Research and Medical Science, Acute Care and Monitoring, Medtronic, Lafayette, Colorado.Roger Martin-Pressman, MA, Clinical Laboratory Manager, Clinical Research and Medical Science, Acute Care and Monitoring, Medtronic, Lafayette; Medtronic Clinical Physiology Laboratory, Denver, Colorado.Michael L. Mestek, PhD, Vice President, Clinical Research and Medical Science, Acute Care and Monitoring, Medtronic, Lafayette, Colorado.