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[Product Review] Contec CMS 50I Pulse Oximeter
Contec CMS 50I Pulse Oximeter

I wanted to review the Contec CMS 50I oxymeter that I have been using for about a month. 

When I wanted to buy an oxymeter to use with OSCAR, there were a few options, some Contec products, some rebranded Contecs and a few others. The CMS 50D, 50F and 50I were the ones that I could find online (Chinese web site) and could import so I had to decide between them. The 50D is a finger type oxymeter so I thought it could be difficult to use while sleeping as this kind of design is for more temporary measurements, so I went for the other options. The 50F and 50I are very similar fuctionally, except the fact that the 50I is newer and it can record multiple sessions (you need to delete the active session on the 50F if you stop recording and restart it). It cost me around 100 USD including free shipping to Turkey, excluding customs (but there is hardly any customs duty to be paid, as the Chinese tend to mis-declare the price of the product, so the tax is around 1-2 USD).

The 50I is shaped like a wirst watch but it is larger than a regular watch, so it might take some time to get used to wear it during sleep. It didn't bother me but I can see people with narrower wirsts having a hader time. The sensor is similar to oximeters used at hospitals: It is a rubber sleeve with the light emitter and sensor embedded inside, and it connects to the oximeter via a short USB cable. I generally put it to my index or middle finger (if I am going to use my tablet before sleeping while I am lying down). This design is more suited for recording during sleep as it doesn't dislocate easily (it never did during my usage period) however some people might find the fit a bit tight. It doesn't bother me during sleep, but in the morning, when I wake up and remove the sensor, I can see the impression of the ribs from the rubber sensor on my finger /disappears in 5 minutes).

The unit has 2 buttons, 1 for turning it on/off, one for navigating the menu (which appears when you press it for a few seconds). Recording a session requires you to going to the recording submenu and select record, which starts the session immediately (it is recommended that you start recording as soon as you start the CPAP, so that you can use it easily with OSCAR). While recording, the display turns off, so that you won't be disturbed by the light if you wake up in the middle of the night and also to preserve battery, but if you want to see your actual SpO2 levels, you can press the menu button and it will turn the screen on for a short time, which I find is usefeul. The menu also has a low SpO2 alarm (and also a PI alarm, both of which can be set to specific values), which I turn off, so that I don't wake up, but some people might find it useful, as it is a sign that things are not ok and might need adjustment.

An advantage of the 50I is its ability to record multiple sessions. I use it to record my O2 saturation during week-ends, when I don't have access to a computer to dump the session from the previous night. Interestingly, I haven't been able to find how big is the memory, nor how many sessions you can record on it at the official web site, nor in the manual. A web site selling the device states that it can record for 24 hours (which will make it similar in length to the 50F but with the advantage of dividing it to sessions, so you can record roughly 3 nights worth of data). The battery life is stated as 10 hours, but there is no mention if this is for the recording mode (where the screen is turned off) or the monitoring mode. My experience is that I can use it for recording for 2 nights (14-15 hours of total sleep) without charging.

While OSCAR supports importing directly from CMS50I, it doesn't work as intended with the actual latest version (v 1.1.1). This problem also exists with the new version of the 50F so, apparently a new hardware or firmware version messed with the import procedure (OSCAR programmers are aware of this and it will probably be fixed in the future). For that reason, you need to use an external software (SpO2 Assistant, which is free and a link is provided when you by the oxymeter) to transfer the data from the oxymeter to the PC, save it and then use OSCAR's import feature. The software also allows syncronizing the oxymeter's internal clock with the PC's clock, so that you can have accurate timing. The software can also be used as a live SpO2 monitor but it isn't possible with the 50I, because it only has 1 USB port and because the finger sensor needs to be connected to that port to record, you can't simultaneously measure SpO2 and be connected to the PC. I don't think this is important for recording sleep sessions, so not really a concern but if you need live monitoring form a PC you need a different oxymeter.

In conclusion, the 50I is a very good oxymeter. It isn't very cheap but works really well. Areas that could be improved would be the total memory (to allow recording for a few weeks, in case you go abroad for more than 3 days), maybe an additional USB port for live monitoring. Also, a replaceable battery could be better for the longevity of the device (the manual states that the battery is rated for 500 cycles, which would mean using it between 500-100 days (1-3 years), but we'll see how long it will last in reality). The CMS50D costs 35 USD and the 50F 92.5 USD (I checked on July 19th from the Chineese web site), so if you are going for this style of oxymeter, I think the 7.5 USD difference is worth the ability to record multiple sessions, so going with the 50I at 100 USD makes sense. Otherwise, the 50D is significantly cheaper, if you can use it while sleeping.
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