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The use of pulse oximetry (SpO2) is ubiquitous. In the United States, it is used continuously for all critically ill patients. Moreover, pulse oximeters can be purchased at any pharmacy and at large mail order consumer sites. Few practicing clinicians recall the time before the mid-1980s when pulse oximeters were not commonly available. I was fascinated by pulse oximeters when they first became widely available, and some of my first clinical research projects were related to the accuracy of pulse oximeters.1,2 Despite improvements such as corrections for motion and low perfusion, the accuracy of pulse oximeters today might not be much better than reported in those early studies. The question might be asked, why the widespread uptake of the use of pulse oximetry? This despite the lack of clear evidence that its use has resulted in improved patient outcomes and concerns about its accuracy.3
In this issue of the Journal are published the results of a clinical study by Blanchet et al4 reporting the accuracy of several pulse oximeter brands in the real-world setting of critical care. They report pulse oximeter inaccuracies that may have important clinical impact on the detection of hypoxemia and management of oxygen administration. I would like to use this study4 as a springboard to discuss several issues related to pulse oximetry.
How to Assess Accuracy of Pulse Oximeters
Accuracy is not defined as correlation. It is possible that two measures of the same signal—for example, hemoglobin oxygen saturation measured by pulse oximetry or by CO-oximetry using an arterial blood sample—might correlate but one or the other might be inaccurate. The accepted approach is that described by Bland and Altman5 that evaluates agreement, not correlation. The Bland-Altman approach calculates bias, precision, and limits of agreement. Bias is the mean difference between SpO2 …
Correspondence: Dean R Hess PhD RRT FAARC. E-mail: hess{at}aarc.org
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