Letters to the Editor: Letters & Announcements
We thank the authors for their interest in our paper and their comments. However, we believe that for the most part they do not address our study specifically, but rather present editorial comments unrelated to the purpose and conclusions of our study. We would, however, like to clarify the one issue regarding the design of our study that they appear to have focused on. It was designed to compare sets of commercially available probes from three manufacturers with prototype probes from OSS. We incorrectly used the word accuracy once in the context of our study, and then only in the abstract, but believe it is clearly stated in the methodology, results, and discussion that we tested variability among specific probes, not absolute accuracy.
We used a “black box” method, looking at inputs and outputs. Inputs are simulated signals applied to the probes, and outputs are the Spo2 values calculated by the monitors. The Index Spo2 tester (Bio-Tek) is designed for this purpose and the 510(k) submission, which we obtained and reviewed in detail before submitting the manuscript, states “The testers can also be used as a transfer standard for pulse oximeters. That is, a pulse oximeter’s performance may be compared to another of the same type or of a different type” (1). The testing includes the probe and the pulse oximeter unit, because with the Index, they are tested together.
We demonstrated by experimentation that we did not add any variability with our experimental design, and thus any variability we measured is caused by differences in probes (most likely due to variability in the LEDs). It is this variability that we have noted in our paper.
We are fully aware of the limitations of the Index tester and clearly stated them in the manuscript. Contrary to the comments of the authors, the tester is not limited to testing for shorts, continuity, opens, and LED functionality. While this is true for the E model of the tester (it does not contain the artificial finger and is limited to testing the electrical signals only), this is not true for the models containing the artificial finger, which is what we used and clearly stated.
We stand by our conclusions that the prototype OSS (Dolphin Medical) probes are equivalent to other manufacturers’ probes and that a simulator can be used to provide input signals for the evaluation of pulse oximeter probes. We agree that these methods are not sufficient to determine absolute accuracy as compared to a “gold standard” such as blood gas analysis.
Johannes H. van Oostrom, PhD
Assistant Professor of Anesthesiology and Biomedical Engineering
Richard J. Melker, MD, PhD
Professor of Anesthesiology, Pediatrics, and Biomedical Engineering
University of Florida; Gainesville, FL
1. Bio-Tek 510(k) Index 2, E, F, EF & CardioSat 100 E, F, EF. FDA approval K971273, obtained under Freedom of Information request.