EBME Forums Forums Maintenance Technical Assistance Testing SpO2 on Mindray monitors

Has anyone had any experience in testing SpO2 with reference to the PI reading?

I am testing a Mindray Benevision monitor using a Fluke prosim-8. When the SpO2 probe is located for the best signal on the simulator all readings are accurate down to 70% (within 2% tolerance)
In this position the PI can be adjusted via the pulse amplitude setting on the simulator – all is good.

However, when the finger probe is slightly adjusted to a poorer position on the simulator this affects the PI.
The Mindray operators manual states that a PI above 1 is optimal, between 0.3 and 1 is acceptable and below 0.3 reposition the probe.

When the PI figure drops below 1, with the simulator set to 70% SpO2 I am seeing the monitor readings go high, sometimes in the 90’s. Following Mindray guidance a low PI is to be ignored so by then repositioning the probe to achieve a PI of above 1 the readings remain high until a PI of around 3 is reached, and only then to the readings fall back into tolerance.

My questions are - is this kind of test, physically moving the probe to adjust the PI a valid test? And could these high readings be seen in a clinical environment on a patient?

I have tried different monitors and different probes and get the same results.

I would say that all is well ... when you have adjusted to a position that gives a poor PI, I imagine that the simulator has to "try harder".

I doubt that such a problem would arise in clinical ("real world") use, as I would expect the clinician to position any "probe" to achieve best results. But you could always check with your friendly nurses.

I would suggest always recording SpO2 test results at the same PI. A bit of "trial and error" should soon point to a preferred value..

I note that "Perfusion Index" does not occur in the ProSim 8 Users Manual ... maybe they did not anticipate this parameter at the time.

FYI:- the Pronk OxSim Flex has provision for selection of perfusion levels, but I note that recommended settings differ for the various "technologies". So, as far as testing is concerned, the whole issue still seems to be somewhat of an art (hopefully one day to become a science).

From the ProSim 8 user manual: "The pulse oximeter component of the (this) device is not intended to
validate the SpO2 accuracy of pulse oximeter equipment"

It does seem that testing SpO2 accuracy seems to be somewhat of an art as you put it Geoff. The more I delve into this the more I realise that how we test SpO2 is merely a function test and can by no means be declared an accuracy check.

Yes; but I would argue that testing (or perhaps more accurately, checking) of biomed equipment is an art!

I can remember when we considered the Rigel 322 as the "bee's knees" when it came to checking out pulse oximeters.

My view is that for routine checking (during ward rounds, for example; or when responding to complaints from users - or even as part of PM), a simple functional check is all that is required. Just as long as you apply a consistency of approach (and maintain records of results); after all, in "science", you need to be able to reproduce results. Then you can generally spot a "wrong 'un" merely by comparison with others of the same type.

The thing about pulse oximeters is that there are so many variables to be considered and (or) simulated. R-curves by different manufacturers, as just one example.

It would be interesting to hear from others regarding which SpO2 test equipment is now "state of the art". Does anyone still use (or even remember) the Lightman?

@Malcolm: The manual for the Fluke ProSim SPOT Light "SpO2 Functional Tester" (which looks very good, and also mentions "perfusion") carries a similar statement.

However, check out this .pdf (which I believe I may have linked to before). See also Dr. Douglas Clarkson.

SPo2 testing is a rather subjective kind of occupation. Really trying to work to definitive numbers is not very useful.
Best advice I could give is to position the probe for the maximum PI and then run through the different % levels as your test script requires. Once the % numbers are checked and are consistent across multiple devices from the same manufacturer then all is well and you can go and award yourself a nice cup of tea!

My main issue is that the Mindray user manual states that a PI of 0.3 to 1 is acceptable and above 1 is optimal. I'm only seeing accurate results, albeit with not the best probe placement possible, with a PI of 3.
I want to be sure that this is a result due to my method of testing and cannot be replicated in a clinical environment on a patient.
Repeating the exact same test on a Masimo Radical 7 I get no issues and all readings are within 2% tolerance of the simulator.
This issue only arose due to our ICU staff reporting higher than expected SpO2 readings compared to the SaO2 blood gas reading.
It would be interesting to see how the manufacturer actually tests SpO2 to achieve ISO 80601-2-61 to get a device on the market. Would it be under perfect lab conditions or do they take into account slight patient movement can happen and how do they measure outside these perfect conditions.

Thanks for posting these. I'd seen that first article before but not the second one. Interesting reading, it really does highlight our testing methods are a mere function check and can't be relied upon as an accuracy check.

Mr Philips he say....
SpO2 Check
NOTE: A functional tester (i.e. simulator or safety analyzer) can not be used to assess the accuracy of an SpO2
probe or an SpO2 monitor.
1 Connect the sensor.
Attach the SpO2 sensor to your finger and to the Efficia DFM100.
2 Turn the Therapy Knob to Monitor. Observe:
a The pleth wave is clear.
b The SpO2 value displayed is in the range of 95-100%. If the value is less than 95%, check that
your finger is fully inserted into the sensor and properly positioned.
c The pulse rate is displayed.