Accuracy and Bias of Pulse Oximetry in the Intensive Care Unit: A Prospective Observational Study

Non-invasive oximetry is crucial for the easy and continuous monitoring of blood oxygenation, from routine assessments to critical care in intensive care units (ICU). Studies indicate that pulse oximeter readings may be biased due to the high light absorption of melanin.

This study aims to analyse the agreement among three different pulse oximeters and their concordance with arterial blood gas measurements in ICU patients and verify how accuracy varies with age and skin pigmentation.

We conducted a prospective cross-sectional observational study with a population of intensive care patients. Blood oxygen saturation was measured simultaneously by pulse oximetry and arterial blood gas analysis. Skin pigmentation was objectively assessed at two anatomical sites using calibrated colorimeters and quantified by the individual typology angle (ITA°).

Among 100 ICU patients (SaO₂ 85%-100%), two of the three oximeters exceeded the 3% accuracy root mean square (ARMS) 2013 FDA threshold, whereas one device remained within limits (2.91%). Agreement with arterial oxygen saturation was weak (CCC = 0.34-0.46) and lower SaO₂ was associated with overestimation increase (0.31%-0.54% for every 1% SaO₂ decrease). Multivariable models showed no evidence of association between ITA° and SpO₂ error (p > 0.05). In contrast, older age predicted greater overestimation (β range = 0.05%-0.06% per year; 95% CI range = 0.02-0.09; all p ≤ 0.05).

Although estimates suggested small pigmentation effects, analysis indicated these were indistinguishable from random error. In contrast, physiological factors such as lower SaO₂ and older age were consistently associated with greater oximeter error. Substantial clinical variability limits detection of small biases, underscoring the need for improved calibration and validation using objective skin-tone assessment.

In intensive care, where continuous monitoring is essential, pulse oximeter error was more strongly related to physiological factors, such as arterial oxygen saturation and age, than to skin tone. These findings support cautious interpretation of SpO₂ values and appropriate device selection to ensure accurate assessment across diverse populations.