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Inverse association between blood pressure and pulse oximetry accuracy: an observational study in patients with suspected or confirmed COVID-19 infection
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    The need for explicit documentation of degree of skin pigmentation

    In an observational study where 200 participants were black, 269 asian, and 4330 white, the authors demonstrated an inverse association between blood pressure and pulse oximetry accuracy that was not influenced by ethnicity[1]. In that study no specific mention was made of the degree of pigmentation in individual members of the ethnic subgroups, presumable because self-reported ethnicity was accepted as a surrogate for skin colour. This acceptance is in sharp contrast with the methodology in the study where subjects of African-American descent were further characterised by a description of their degree of pigmentation, using terminology such as "very darkly pigmented".. This was one of the earliest prospective studies conclusively to show that some oximeters overestimate arterial oxygen saturation in hypoxic subjects who are "darkly pigmented" [2].
    In retrospective studies such as the ones subsequently undertaken to explore the theme of racial bias in oximetry it was easy to fall into the trap of using ethnicity as a surrogate for skin colour[3],[4], largely because skin colour is not consistently recorded as part of the medical record[3]. Explicit description of skin colour also gets omitted when race and ethnicity are defined using self-reported demographic data[4].
    Future studies, however, might seek to ascertain whether or not skin pigmentation compounds the overestimation of oxygen saturation attributable to hypotension....

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    Conflict of Interest:
    None declared.