Evaluation of the accuracy of pulse oximeters in real clinical settings

Introduction
 Pulse oximeters are indispensable devices for noninvasive monitoring of arterial blood oxygen saturation (SpO$_2$); however, verification of their accuracy still relies on invasive CO-oximetry performed under controlled desaturation protocols, which are impractical for routine clinical use. Although functional testing using pulse oximeter simulators is widely employed as a surrogate approach, such simulators generally lack direct metrological traceability to CO-oximetry.
 
 Objectives
 This study evaluated the accuracy of five commercial pulse oximeters under routine clinical conditions at three hospitals, using site-specific CO-oximeters as reference analyzers. The objectives were to characterize real-world pulse oximeter accuracy without induced desaturation, to examine the potential for metrological traceability of arterial blood oxygen saturation measurements obtained from pulse oximeters with respect to the gold standard, and to assess the suitability of selected pulse oximeters as candidate secondary reference devices for traceable and noninvasive verification.
 
 Approach
 A total of 488 paired SpO$_2$--SaO$_2$ measurements were collected from 148 hospitalized patients during routine care. Accuracy metrics, including bias, mean absolute error (MAE), root-mean-square accuracy ($A_{rms}$), Bland--Altman limits of agreement (LoA), and concordance correlation coefficient (CCC), were calculated for each site and for a pooled dataset. 
 
 Results
 Across all reference systems, the five pulse oximeters exhibited $A_{rms}$ values between 2.1% and 2.7%, well within the acceptance limits specified by ISO~80601-2-61 (4%) and the U.S.~Food and Drug Administration (FDA) (3%). Measured accuracy remained broadly consistent across pulse oximeter models and reference CO-oximeters when standardized handling procedures were applied. Only minor inter-site differences were observed, demonstrating that consistent multicenter evaluation is feasible under routine clinical conditions within the SaO$_2$ range of approximately 80--100\%. 
 These findings provide preliminary support for the future evaluation of selected pulse oximeters as candidate secondary reference devices and for the development of traceable, noninvasive verification approaches using calibrated simulators.