EquiOx: A Prospective study of pulse oximeter bias and skin pigmentation in critically-ill adults

RationalePulse oximeter performance may vary by skin pigmentation, but most data are retrospective with key limitations. ObjectiveTo quantify pulse oximeter bias [mean difference between pulse oximeter oxygen saturation (SpO2) and arterial blood functional oxygen saturation (SaO2)], and average root mean square error (ARMS) and estimate adjusted effects of skin pigment on bias or ARMS in critically-ill adults MethodsProspective single-center study of 631 ICU patients (2022-2024) directly observed SpO and SaO pairs. Skin pigment was assessed using the subjective Monk Skin Tone Scale and objective spectrophotometry measurement (Individual Typology Angle [ITA]). Adjusted effects were estimated with targeted maximum likelihood estimation. Main ResultsAmong 1,760 paired measurements from 631 critically-ill adults, median SaO2 was 98% (IQR 96%, 99%) with 40 episodes of stable hypoxemia (SpO2<90%). SpO2 systematically underestimated SaO2 [median bias= -1.70 IQR (-2.84, -0.50)]. Bias was less negative in patients with darker skin (ITA <-30{degrees}) [-1.05 (-2.44, -0.10)] vs lighter skin (ITA >30{degrees}) [-2.01 (-3.34, -1.00)] and remained significantly different in adjusted analyses. ARMS was 3.87 (95% CI 3.25, 4.53) overall and 4.49 (95% CI 2.63, 7.07) in patients with darker skin. Ear probes performed worse than finger probes [bias: -2.20 vs. -1.60; ARMS: 4.90 vs. 2.70]. ConclusionsIn this large ICU cohort, hypoxemia was rare, pulse oximeters systematically underestimated SaO, performance varied by skin pigment and probe site. Bias was less negative in patients with darker skin. Pulse oximeter inaccuracies in ICU patients may be more substantial than clinicians recognize. Key PointsO_ST_ABSQuestionC_ST_ABSDoes pulse oximeter bias in critically-ill adults differ by skin pigmentation? FindingsIn this prospective, single-center study of 631 critically-ill adults, oximeter mean bias was negative for all patients but relatively less negative for patients with darker pigment. Bias variation by pigment was nonlinear and larger in ear than finger probes. MeaningPulse oximeter bias varies with skin pigmentation and may not always be positive in patients with darker pigmentation. Pulse oximeter inaccuracy may be larger than clinicians appreciate. Additional studies with multiple oximeter brands and more stable hypoxemia are needed to further understand bias variation with skin pigment.