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

<bold>Background:</bold> Recent studies have found that Black patients are more likely to have falsely normal oxygen saturation on pulse oximetry compared to White patients. We aimed to study whether racial differences in measuarable clinical factors are associated with the racial difference in the prevalence of occult hypoxemia. <bold>Methods:</bold> We conducted a retrospective case-control study utilizing two large ICU databases (eICU and MIMIC-IV). We defined occult hypoxemia as oxygen saturation on pulse oximetry below 90% despite oxygen saturation on arterial blood gas within 92-98%. We assessed associations of commonly measured clinical factors with occult hypoxemia, using univariable and multivariable models. <bold>Results:</bold> Among 24,641 patients, there were 1,855 occult hypoxemia cases and 23,786 controls. In both datasets, self-reported Black patients were more likely to have occult hypoxemia (unadjusted odds ratio 1.66 [95% CI: 1.41, 1.95] in eICU and 2.00 [95% CI: 1.22, 3.14] in MIMIC-IV). In univariable models, we observed associations of occult hypoxemia with higher heart rate, higher respiratory rate, lower temperature, lower arterial pH, higher PaCO2, lower Hgb, higher MCV, lower MCHC, higher bicarbonate, and higher creatinine. Of these, Black patients were more likely to have a higher heart rate, respiratory rate, creatinine, and lower hemoglobin and MCHC. In multivariable models, higher respiratory rate, PaCO2 and creatinine as well as lower hemoglobin were consistently associated with increased odds of occult hypoxemia. <bold>Conclusion:</bold> Clinical differences, in addition to the effect of skin tone, may play a role in the increased prevalence of occult hypoxemia in Black patients.