Recording Pulse Oximeter

[bb60]

I recently purchased a Contec CMS50FW recording pulse oximeter. It is reading about 4 points low on the pulse ox. In the manual it says to calibrate it periodically, but doesn't say how to do it. It came from China and support has been non existent so far. I kind of like it except for the inaccurate readings and don't really want to send it back if I can find out a way to calibrate it. If anyone knows how to calibrate one of these I'd appreciate your sharing.

Thanks,

[LSAT]

I recently purchased a Contec CMS50FW recording pulse oximeter. It is reading about 4 points low on the pulse ox. In the manual it says to calibrate it periodically, but doesn't say how to do it. It came from China and support has been non existent so far. I kind of like it except for the inaccurate readings and don't really want to send it back if I can find out a way to calibrate it. If anyone knows how to calibrate one of these I'd appreciate your sharing.

Thanks,

How do you know that it is recording low?

[bb60]

I simultaneously compared it to another one that I knew to be accurate. The readings I was getting if correct would be very close to respiratory failure.

[STL Mark]

I simultaneously compared it to another one that I knew to be accurate. The readings I was getting if correct would be very close to respiratory failure.

Wow, just 4 points away from respiratory failure. Sorry to hear things are that bad for you. One way to calibrate the readings may be to add 4 points to the readings.

[HoseCrusher]

Since you just got it, return it as defective.

[Stormynights]

I returned one to China for repair and they said they never got it. All the tracking information I could get just showed it made it to China, no proof whether they got it or not. It would just be easier to add the numbers.

[HoseCrusher]

My point is that I believe that oxygen levels and pulse rates are important. If your measuring equipment isn't reading correctly I think there is too much at stake to try and get by with a work around.

If you are afraid to return it, toss it in the garbage and purchase another one from a supplier that will take a return if needed. The few extra dollars you spend will be well worth it.

One of the advantages of having an oximeter is that you can print out reports. Those reports are easily understood by all doctors however if there are questions about accuracy they will not even look at the reports. Accuracy goes a long way to credibility and this matters in the medical world.

With that said I have two additional comments...

When you get a device to measure body functions you need to check it out. A good way to do this is to visit a doctor that has access to similar devices. That way you can have your doctor check your device out for accuracy. This builds a type of bond between you and your doctor and instills more willingness to work with you and to look at your reports.

The second involves developing a correction curve to address your calibration issues. The fire department paramedics use oximeters. Ask around and see if you can find a fire fighter that is sympathetic to your cause. In my area I have simply gone down to the fire station and struck up a conversation with them and they were very willing to work with me. I have worked with them on 3 different devices: my blood pressure machine, my oximeter, and my "hobby" EKG device.

In addition my doctor has access to similar devices. I started off by informing my doctor that I was going to check the accuracy of my devices and was planning on bringing in reports for discussion. I asked if there were any concerns and gave my plan for checking accuracy. My doctor encouraged me to follow my plan and also offered to cross check my devices during one of my well checks.

Fortunately all my devices were accurate when compared to both the doctors and the fire fighters equipment.

With an oximeter that is not accurate and if it is a major problem to replace it with one that is properly calibrated you can do a calibration curve. This involves comparing your read out with a calibrated read out over the range of the instrument. This involves a lot of work because you have to by hyper and hypo ventilate to go over the range of oxygen saturation that you are interested in. For example you would try to desaturate down to about 88% on the good meter and see what your meter reads. You do the same thing at 90%, 94%, and 98%. You then plot the data to see if it is linear. If it is linear then you can print your report and attach a copy of your calibration curve and go with that. You would have to adjust the scoring values used in the report and attach a note why those values were adjusted.

Having played with this over an extended period of time I can tell you this is very hard to do. It is easy to hyperventilate but to drop your oxygen levels by holding your breath and holding a low level long enough to get a stable reading can be very difficult.

Another issue is that the oximeter is only accurate over a narrow range. I seem to remember that accuracy drops off below about 90%. If you are reading 6% low you may be off by more than that and the deviation may not be linear.