# Pulse Oximetry, does the decimal matter?

I work in a sleep research lab. We have a couple of Masimo pulse oximeters that report pulse oximetry values in terms of integers (e.g. 90, 91, 92, etc.).

Now our principle investigators used to use an Ohmeda Biox 3700 that reported data via analog output in a nice (noisy) curve (e.g. after filtering, 90, 90.1, 90.3, 90.4, etc.).

There's some discussion that because of the lack of decimal, the Masimo is useless for data reporting. The Ohmeda though is from the 90s and I can't find any documentation that indicates if taking the decimal is even acceptable for the device's resolution. Any thoughts?

• Possible cross-site duplicate of biology.stackexchange.com/questions/82301/… – tripleee Mar 27 '19 at 19:12
• This really is a medical question not an engineering question. – Eric S Mar 28 '19 at 14:25
• This is not a medical question - it is an engineering question. It's really about making a practicable device, and how the manufacturer has swept all the fudges under the carpet. It's a question about noise and how small changes in a measurement propagate. What's the variance in the the photodiode outputs at the wavelengths used for the pulse oximetry? How to propagate forward to the calculation of SpO2 and how this is related to the absorption and scattering coefficients of blood and tissue? It's specmanship - my device has an extra decimal point, so it must be better. – D Duck Mar 29 '19 at 9:12
• @DDuck There is a difference between accuracy and precision. If the extra decimal place doesn’t make any medical treatment difference then it is unimportant. – Eric S Mar 31 '19 at 2:34
• It is important is for the sales people. The implication is that this device is better because it is more accurate and/or precise than the competitors product. – D Duck Mar 31 '19 at 17:22

The accepted error in pulse oximtery isn't that good. It's about $$\pm$$2 % so your additional significant figures are useless. A good review is Aoyagi, T. J Anesth (2003) 17: 259. https://doi.org/10.1007/s00540-003-0192-6