Common pulse ox myths

Studies have shown that many low-cost pulse oximeters demonstrate highly inaccurate readings. However, some low-cost pulse oximeters have performed with similar accuracy to more expensive devices when used in healthy subjects. Please see our oximeter database for performance information on many low cost oximeters. 

References: Lipnick et al, Anesth Analg 2016

Keywords: low-cost, low cost, cheap, inaccurate

The short answer is no. There is no such thing as a pulse oximeter simulator and none can reliably predict clinical performance for all oximeters.

There are several devices that exist to ‘simulate’ or ‘test’ pulse oximeter function including the Fluke ProSim SPOT, Fluke ProSim8 and Whaleteq AECG100. 

These devices work by detecting LED pulses from an oximeter, then fabricating their own output signal to the oximeter sensor. The Fluke preserves any noise in the LED light signal while the others simply trigger from it and in doing so eliminate all potential errors due to LED noise (a very common problem with implications for oximeter performance). Some of these devices also have a limited range of simulated conditions (ie perfusion) and require prior calibration to the specific oximeter being tested. Thus, for oximeters already calibrated into the in vitro simulator, the simulator can help confirm that a device is working (or at least is sensing signal) as it was designed to do in the factory. For devices not previously calibrated, conclusions about performance are uncertain. 

Multiple studies report to have used these devices to ‘validate’ oximeter performance, yet performance of an uncalibrated oximeter on an in vitro simulator does not ensure good oximeter performance in reality. 

Simulators of this type are useful for determining the operating range of an oximeter.  For example the limits in terms of dark skin and low perfusion can be found.  One can determine if the device reads an erroneous value when pushed beyond its effective range or if it reports nothing.

The OpenOximetry.org Project is working to develop novel in vitro testing devices and protocols that overcome the limitations of prior devices. The hope is that newer techniques can better augment human study subject testing and predict device performance. 

Read here for more on oximeter performance validation requirements

Most pulse oximeters do not need to be calibrated by the user before they will work properly. During device development, the microprocessors of pulse oximeters are calibrated using reference SaO2 measurement data that are compiled from healthy volunteers. Volunteers are typically exposed to different levels of inspired oxygen to yield SaO2 ranging from around 75 to 100%. 

There are devices such as the Fluke ProSim 8 that are designed to check if select manufacturers’ oximeters are functioning, but are not designed to validate accuracy.

References: Lifebox Pulse Oximetry Learning Module

Keywords: calibration

Not necessarily. This commonly recited myth stems from the fact that oximeters are only tested in clinical validation studies down to 70% SpO2 due to the stated requirement by the FDA and also because of limitations by institutional review boards. So, while oximeters are not usually validated clinically below SpO2 70%, and oximeter performance becomes less accurate at lower SpO2, oximeter readings below 70% should not be disregarded. Widely inaccurate SpO2 values below ~SpO2 70% are more often due to poor signal in the context of a critically ill patient with poor perfusion, rather than an inherent limitation in inherent oximeter technology. 

Keywords: accuracy, inaccurate