O2043: Pulse Oximetry and Skin Tone in Children (POSTer-Child): The first 100 patients

Background: Recent retrospective studies have demonstrated overestimation of oxygen saturation by pulse oximetry in patients with darker skin. This can lead to disparities in care and contribute to racial inequities in outcomes. Existing studies have used race as a proxy for skin tone, which is known to be a poor surrogate. Further, these retrospective studies matched pulse oximetry values to blood gas measurements using timestamps, which may introduce significant error. We aim to directly measure skin tone to quantify its effect and develop a model to correct for this overestimation.

Methods: Consecutive patients under 21 years of age presenting for cardiac catheterization were prospectively enrolled. Skin tone was measured using the validated Fitzpatrick color scale (1=lightest, 6=darkest) and a spectrophotometer (Konica Minolta CM-700d). Skin tone was measured in triplicate on the dorsal aspect of the index finger. Melanin index and individual typology angle (ITA) were used for analyses. Pulse oximetry (SpO2) values were recorded at the time of arterial blood gas sampling under direct observation. SpO2 values were recorded using two different pulse oximeters (Nellcor and Masimo). Arterial saturation (SaO2) was directly measured using an oximeter (Avoximeter 1000E). To quantify the overestimation of saturation from skin tone, multivariable linear regressions were performed with SaO2 as the dependent variable and SpO2 and skin tone measurements as independent variables. Regressions were adjusted for factors known to affect pulse oximetry accuracy. This study was approved by the VUMC IRB (#231423).

Results: Most participants identified as white, although more than 20% of the cohort identified as another race or ethnicity (Table 1). Most had either Fitzpatrick type 2 or 3 skin color. All patients had congenital heart disease, including 16 who had hypoplastic left heart syndrome. Pulse oximetry overestimation increased with increasing Fitzpatrick skin type (p < 0.01), including a mean overestimation of SaO2 by 5.6% for Nellcor and 7.8% for Masimo among patients with Fitzpatrick type 6. Similarly, those in the darkest quartile for melanin index had the greatest overestimation with a mean of 2.6% for Nellcor and 3.7% for Masimo. Both ITA and melanin index were independently associated with overestimation of saturation. The predicted overestimation for the darkest quartile of patients by melanin index was 3.1% for Nellcor and 3.7% for Masimo (Figure 1).

Conclusion: This represents the first prospective study in children with congenital heart disease measuring the overestimation of saturation by pulse oximetry attributable to skin tone. Both ITA and melanin index were independently associated with overestimation. These errors were clinically significant, with mean overestimation greater than 5% in participants with the darkest skin. This overestimation could lead to significant undertreatment of hypoxia and contribute to inequities in health outcomes. Our findings underline the importance of better pulse oximeter validation among patients with darker skin.