Letters to the Editor: Letters & Announcements
To the Editor:
We read with interest the study of pulse oximeter probes (1), but must take exception to the study’s methodology and conclusions. The study was intended to evaluate and compare the accuracy of prototype nonproprietary probes (OSS/Dolphin Medical) to their counterpart proprietary sensors from the original equipment manufacturers (Nellcor, Datex-Ohmeda, and Criticare). The protocol used a bench-top patient simulator (BioTek Index) to compare the various sensors’ pulse oximeter Spo2 readings with the simulator set points. The study’s conclusions suggest equivalence or superiority of performance in nonproprietary probes.
Unfortunately, the authors have grossly misinterpreted the ability of this simulator to evaluate the probe’s contribution to Spo2 reading accuracy. While the Index and several other commercially available patient simulators can test sensor and pulse oximeter functionality, they are incapable of providing the required data needed to properly evaluate the accuracy of Spo2 readings (according to a letter to Nellcor Puritan Bennett from Peter M. Weith, BioTek Instruments, October 1995). With respect to pulse oximeter probes, the patient simulator used in the study is capable only of “testing for shorts, continuity, opens and LED functionality” (2). Evaluating Spo2 reading accuracy would require, at a minimum, accommodating the wavelength characteristics of the sensor and reproducing the complex optical interaction of the sensor and the patient’s tissue.
There are no bench-top simulators available today that can provide the data the authors would need to support their conclusion. The ASTM and ISO Committees for developing pulse oximetry standards have recognized the issue of bench-top accuracy testing (3), and an effort supported by the European Union to create such a device is currently underway (4,5). We are aware of only one validated method to assess Spo2 reading accuracy—direct comparison to sampled arterial blood Sao2 measured using a laboratory co-oximeter.
We therefore disagree with the authors’ two conclusions; their study demonstrates neither equivalency of the nonproprietary probes, nor that a simulator can be used to evaluate pulse oximetry probe accuracy.
Paul D. Mannheimer, PhD
Research and Development Department
Nellcor Puritan Bennett, a part of Tyco Healthcare
Paul B. Batchelder, RRT
Head of Clinical Research
Pulse Oximetry Center of Excellence
Datex-Ohmeda, GE Medical Systems
Vice President - Quality
Criticare Systems, Inc.
Hartmut Gehring, MD
Professor of Anesthesiology
Department of Anesthesiology
University of Lübeck
Ewald Konecny, PhD
Institute of Biomedical Engineering
University of Lübeck
1. van Oostrom JH, Melker RJ. Comparative testing of pulse oximeter probes. Anesth Analg 2004;98:1354–8.
3. International Organization for Standardization (ISO). Simulators, calibrators and functional testers for pulse oximeter equipment. ISO TC 121/SC 3, Draft International Standard 9919, Annex FF, 2003.
4. Hornberger C, Knoop P, Nahm W, et al. A prototype device for standardized calibration of pulse oximeters. J Clin Monit 2000;16:161–9.
5. Hornberger C, Knoop P, Matz H, et al. A prototype device for standardized calibration of pulse oximeters II. J Clin Monit 2002;17: 203–9