• 
• 

Three Part Question

In [adults and children with different skin pigmentation] what is the [accuracy of arterial oxygen saturation] measured by pulse oximetry compared with the gold standard [SaO2 measured by CO-oximetry]?

Clinical Scenario

An African American 19-year-old male presents to the emergency department with coryza, audible wheeze, and cough. He is afebrile, well hydrated, in mild respiratory distress with an oxygen-saturation (SaO2) 93% on room air. During the COVID-19 pandemic, you recall some concerns regarding potential bias in pulse oximetry measurements for people with high levels of skin pigmentation.

Search Strategy

Medline 1966-09/24 using PubMed, Cochrane Library (2024), and Embase
[(oxygen saturation.mp AND skin pigmentation.mp)]. LIMIT to adults and English language.

Search Outcome

81 total articles were found, three systematic reviews and one clinical trial were identified as both relevant and of sufficient quality for inclusion.

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses
Martin D, et al May 2024 UK	Forty-four studies with 222,644 participants enrolling adults and children when SpO2 was compared with a paired co-oximetry SaO2 value.	Systematic review	Overestimation of SaO2 in participants with darker skin tones	68% (30/44) of studies	Meta-analysis was not possible because of heterogeneity in study design, population, pulse oximeter make, and data reported; the magnitude of overestimation of SaO2 in participants with darker skin tones was difficult to determine; only 11 (25%) studies actually measured skin tone.
			Magnitude of overestimation of SaO2 in participants with darker skin tones	The magnitude varied between studies, lower SaO2 was associated with a greater degree of overestimation
Shi C, et al August 2022 UK	32 studies (6505 participants) with SpO2–SaO2 comparisons and measuring the impact of skin pigmentation or ethnicity on pulse oximetry accuracy	Systematic review and meta-analysis	Overestimated SaO2 in people with the darkest skin tones	Mean 1.11%; 95% confidence interval 0.29–1.93%	Some included studies compared SpO2-SaO2 data between different subgroups of skin pigmentation and presented only tests of significance, rather than SpO2 and SaO2 data; scales like the Fitzpatrick scale to measure levels of skin pigmentation are limited; differences between specific pulse oximeter devices, the differences between adults and their health conditions or the difference between skin pigmentation measurement methods were not considered.
			Overestimated SaO2 in Black/African American	Mean 1.52%; 95% confidence interval 0.95 to 2.09%
Aoki KC, et al September 2023 USA	10 prospective and retrospective studies involving human patients with hypoxemia that included a measure of skin color	Scoping review	SpO2 readings vs. SaO2 values for patients of darker skin pigments	SpO2 readings in dark vs. light-skinned individuals were approximately 1% to 1.57% higher	Some studies lacked specific race and ethnicity data and most studies used self-reported race to categorize patients; small sample sizes and a lack of racial diversity were also limitations in several studies; most studies focused on adult populations and did not account for underlying diseases that might affect SpO2 readings.
			Agreement between SpO2 measurements and SaO2 with hypoxia	Error that increases if SaO2 values decrease to hypoxemic levels
Leeb G, et al April 2024 USA	Eleven fingertip pulse oximeters were evaluated in 34 healthy humans with diverse skin pigmentation utilizing a controlled desaturation study.	Prospective clinical trial	SpO2-SaO2 error between devices	Five of 11 devices had a root mean square error (ARMS) > 3%, falling outside the acceptable FDA performance range	Participants were young, healthy adults which do not reflect the heterogeneity of anatomy and pathophysiology of patients with an illness or people with comorbidities; perfusion (i.e. pulsatility amplitude), a factor known to impact POX performance, was not accounted for; relatively few pulse oximetry sensors were tested; low number of individuals recruited with dark skin.
			SpO2-SaO2 error between devices among participants in the darkest skin pigmentation category compared with those in the lightest category	Seven of the 11 POXs tested and the reference POX demonstrated a positive bias among individuals with darker pigmentation

Comment(s)

Much of the evidence suggests that the accuracy of pulse oximetry using a conventional finger sensor varies in patients with different skin pigmentations. Current FDA guidance and ISO standards do not adequately account for the potential impact of skin pigmentation on pulse oximetry performance. Subsequently, overestimation of oxygen saturation, particularly in hypoxic states, is disparately higher in Hispanic and Black patients compared to other racial groups. Asian and American Indians are also more likely to have a SaO2 < 88% that was not detected by pulse oximetry (occult hypoxemia) during hospitalization. With greater levels of hypoxemia, the differences between SaO2 and SpO2 are greater.

Clinical Bottom Line

Clinicians should recognize the limitations of pulse oximetry and use additional objective measures of oxygenation (like co-oximetry measured arterial oxygen saturation) where hypoxia is a concern in patients with different skin pigmentations.

References

1. Martin D, Johns C, Sorrell L, Healy E, Phull M, Olusanya S, Peters M, Fabes J. Effect of skin tone on the accuracy of the estimation of arterial oxygen saturation by pulse oximetry: a systematic review. Br J Anaesth. 2024 May;132(5):945-956
2. Shi C, Goodall M, Dumville J, Hill J, Norman G, Hamer O, Clegg A, Watkins CL, Georgiou G, Hodkinson A, Lightbody CE, Dark P, Cullum N. The accuracy of pulse oximetry in measuring oxygen saturation by levels of skin pigmentation: a systematic review and meta-analysis. BMC Med. 2022 Aug 16;20(1):267.
3. Aoki KC, Barrant M, Gai MJ, Handal M, Xu V, Mayrovitz HN. Impacts of Skin Color and Hypoxemia on Noninvasive Assessment of Peripheral Blood Oxygen Saturation: A Scoping Review Cureus 2023 Sep 27;15(9):e46078
4. Leeb G, Auchus I, Law T, Bickler P, Feiner J, Hashi S, Monk E, Igaga E, Bernstein M, Chou YC, Hughes C, Schornack D, Lester J, Moore K Jr, Okunlola O, Fernandez J, Shmuylovich L, Lipnick M. The performance of 11 fingertip pulse oximeters during hypoxemia in healthy human participants with varied, quantified skin pigment. EBioMedicine 2024 Apr;102:105051