Exclusion of Patients Limits Findings in Pulse Oximeter Study

Fernandez and colleagues¹ compare forehead reflectance pulse oximetry and finger transmittance pulse oximetry in a group of critically ill patients with low cardiac index. The data appear to show that oxygen saturations from forehead oximetry were statistically closer to blood gas analysis than were data derived from finger oximetry; however, the differences are clinically irrelevant. Based on these data, the authors conclude that forehead oximetry is “better” than finger oximetry for this group of patients.

However, a methodological flaw may have affected the study’s results. Patients who required Trendelenberg positioning for shock were excluded a priori from entering the study. Unfortunately, the reader cannot know how many patients were screened and excluded for this reason, because these data are not provided. Having the patient’s head lowered for any reason (eg, postural drainage, central line insertion) can affect the accuracy of forehead reflectance oximetry due to venous congestion.^2,...