Quantifying Pulse Oximeter Accuracy During Hypoxemia and Severe Anemia Using an In Vitro Circulation System

Purpose: Anemia and hypoxemia are common clinical conditions that are difficult to study and may impact pulse oximeter performance. Utilizing a novel in vitro circulation system (IVCS), we studied performance of three pulse oximeters during hypoxemia and severe anemia. Methods: Three oximeters were selected to reflect a range of cost (Masimo Radical 7 with Masimo LNCS Adtx sensor, Acare AH-M1 and Contec CMS 50-DL). Human blood was diluted to generate four hematocrit (Hct) levels (40%, 30%, 20%, and 10%). Oxygen and nitrogen were bubbled through the blood to generate a range of oxygen saturations (O2Hb) and the blood was cycled through the IVCS. Pulse oximeter saturations (SpO2) were paired with simultaneously-measured O2Hb readings from a reference CO-oximeter. Data for each Hct level and each device were least-squares fit to a 2nd-order equation with quality of each curve fit evaluated using standard error of the estimate. Bias and average root mean square error were calculated after correcting for the calibration difference between human and IVCS calibration. Results: The benchtop oximeter (Masimo Radical) maintained good accuracy at all but the most extreme level of anemia. The handheld device (Acare AH-M1) was not as accurate as the Masimo, and inaccuracies increased at lower Hct levels. The fingertip device (CMS 50-DL) was the least accurate of the three oximeters. Conclusion: Pulse oximeter performance is impacted by severe anemia in vitro. The use of in vitro calibration systems may play an important role in augmenting in vivo performance studies evaluating pulse oximeter performance in challenging conditions.