Low perfusion and missed diagnosis of hypoxemia by pulse oximetry in darkly pigmented skin: A prospective study

Abstract

ImportanceRetrospective clinical trials of pulse oximeter accuracy report more frequent missed diagnoses of hypoxemia in hospitalized Black patients than White patients, differences that may contribute to racial disparities in health and health care. Retrospective studies have limitations including mistiming of blood samples and oximeter readings, inconsistent use of functional versus fractional saturation, and self-reported race used as a surrogate for skin color. Understanding the cause of biased readings by pulse oximetry in patients with darkly pigmented skin is high priority given the essential nature of pulse oximetry.ObjectiveTo prospectively measure the contributions of skin pigmentation, perfusion index, sex, and age on pulse oximeter errors.DesignWe studied two pulse oximeters (Nellcor N-595™ and Masimo Radical 7™) in prevalent use in North America, Europe, and Asia-Pacific regions. We analyzed 9,763 matched pulse oximeter readings (SpO2) and arterial oxygen saturation (hemoximetry SaO2) during stable hypoxemia (SaO2 68-100%). Perfusion index (PI) was measured as percent infrared light modulation by the pulse detected by the pulse oximeter probe, with low perfusion categorized as PI <1%.SettingClinical research laboratoryParticipants146 healthy subjects, including 25 with light skin (Fitzpatrick class I-II), 78 with medium (class III-IV), and 43 with dark (class V-VI) skin.ExposuresControlled hypoxemiaMain OutcomesPulse oximeter bias (difference between SaO2 and SpO2) by skin pigment category in a multivariable mixed-effects model incorporating repeated-measures and different levels of SaO2 and perfusion.ResultsSkin pigment, perfusion index and degree of hypoxemia significantly contributed to errors (bias) in both pulse oximeters. The combined frequency of missed diagnosis of hypoxemia (pulse oximeter readings 92-96% when arterial oxygen saturation was <88%) in low perfusion conditions was 1.1% for light, 8.2% for medium and 21.1% for dark skin.Conclusions and RelevanceLow peripheral perfusion combined with darker skin pigmentation leads to clinically significant high-reading pulse oximeter errors and missed diagnoses of hypoxemia. Darkly pigmented skin and low perfusion states are likely the cause of racial differences in pulse oximeter performance in retrospective studies. Both skin pigmentation and low perfusion should be accounted for in regulatory standards for pulse oximeters.Key PointsQuestionLaboratory validation of pulse oximeter performance has found errors in Black subjects that are smaller than those from recent reports of hospitalized Black patients. We test the hypothesis that low perfusion amplifies pulse oximeter error in subjects with dark skin during hypoxemia.FindingsDark skin pigmentation combined with low perfusion produces large errors in pulse oximeter readings in healthy subjects during hypoxemia, sufficient to miss a diagnosis of hypoxemia in about 20% of readings.MeaningAccuracy of pulse oximeters in the diagnosis of hypoxemia is impaired by a combination of low perfusion and dark skin pigmentation. Low perfusion should be accounted for in future testing and regulatory guidelines for pulse oximeters to improve performance and minimize bias in patients with dark skin pigment.

Effect of skin tone on the accuracy of the estimation of arterial oxygen saturation by pulse oximetry: a systematic review

“…Evaluation of skin tone only occurred in three studies. 18 , 19 , 20 The proportion of participants with darker skin tones or of non-White ethnicities was particularly low in earlier studies ( Supplementary Table S2 ). One study comprised 100% Black participants.…”

“… 57 One of these three studies presented bias data and reported a consistent underestimation of true SaO 2 in a cohort of 33 Black participants with a maximum bias of –7.1 (9.0)%. 20 , 24 , 25 , 27 , 31 , 33 , 35 , 36 …”

Clinical factors associated with racial differences in the prevalence of occult hypoxemia: a retrospective case-control study

“…Our results suggest that Black patients may be sicker when they are treated in intensive care units, and racial disparities in the delivery of critical care medicine may be contributing to the racial difference in the prevalence of occult hypoxemia. Notably, a recent study by Gudelunas et al suggested that low perfusion state is a significant contributor to the pulse oximetry errors when combined with darker skin pigmentation (21).…”

Oxygen saturation targets for adults with acute hypoxemia in low and lower-middle income countries: a scoping review with analysis of contextual factors

“…The studies above demonstrate that not only is there significant bias in measurement of oxygen saturation in individuals with darker skin tones, it also translates into poorer healthcare delivery and clinical outcomes for these patients, which further perpetuates health inequities. The literature also highlights that the magnitude of inaccuracy with different skin tones is variable and not well-quantified, differing by device and other patient factors, including low perfusion ( 49 , 58 ). These studies were all performed in HICs, and there is a critical paucity of such data in LMICs.…”

“…Bias in pulse oximetry measurements Pulse oximetry (SpO 2 ) does not perfectly correlate with arterial oxygen saturation (SaO 2 ) as measured by blood gas, and prior studies have found multiple potential sources of inaccuracy, particularly as patients become sicker, as denoted by rising lactate and hypoxia (48,49). These include severe hypoxemia, low perfusion, patient movement, and severe anemia.…”