Work

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

Year: 2025

Type: preprint

Abstract: Rationale Pulse oximeter performance may vary by skin pigmentation, but most data are retrospective with key limitations. Objective To quantify pulse oximeter bias [mean difference between pulse oximeter oxygen saturation (SpO 2 ) and arterial blood functional oxygen saturation (SaO 2 )], and average root mean square error (A RMS ) and estimate adjusted effects of skin pigment on bias or A RMS in critically-ill adults Methods Prospective 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 Results Among 1,760 paired measurements from 631 critically-ill adults, median SaO 2 was 98% (IQR 96%, 99%) with 40 episodes of stable hypoxemia (SpO 2 <90%). SpO 2 systematically underestimated SaO 2 [median bias= −1.70 IQR (−2.84, −0.50)]. Bias was less negative in patients with darker skin (ITA <-30°) [−1.05 (−2.44, −0.10)] vs lighter skin (ITA >30°) [−2.01 (−3.34, −1.00)] and remained significantly different in adjusted analyses. A RMS 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; A RMS : 4.90 vs. 2.70]. Conclusions In 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 Points Question Does pulse oximeter bias in critically-ill adults differ by skin pigmentation? Findings In 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. Meaning Pulse 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.

Source: medRxiv

DOI: 10.1101/2025.10.06.25337217