ResMed CPAP masks and Dexcom CGM

I just got a letter from my CPAP supply company alerting me that there’s a potential issue with ResMed CPAP masks that use magnetic clasps interfering with implanted medical devices with ferromagnetic components. The letter refers to pacemakers and insulin pumps, but does not mention CGMs. It says devices could be affected if they’re within 6 inches of the mask’s magnets.

I switched this month from having a Dexcom G6 in my abdomen to putting a G7 in my arm. I sleep with my arm under the pillow, so the CGM is sometimes within the 6 inch range. I saw a post elsewhere saying that the G7 in particular uses a magnet to alert the transmitter to begin the sensor session. If you look inside the G7 applicator there’s a small circular magnet near the outer edge of the applicator. When the sensor is implanted, it detaches from the applicator and the removal of the magnet alerts the sensor to start the session. I don’t think that you can trigger it to restart a sensor session or turn the sensor off by magnetizing it again, but it does show that the transmitter uses magnetically sensitive components.

Here’s the thing: When I switched to the G7, the pump started waking me up with an alarm saying that it had lost contact with the CGM for an extended period. I shifted the position of where I keep the pump, and that’s helped, but it still happens sometimes.

I’m not certain, but I think there’s a possibility (which I reported to the FDA using the link from ResMed’s notification letter) that the magnet from the CPAP mask might be interfering with the G7 transmitter.

I’m okay. They’re sending me a new, non-magnetic mask. But I thought I’d mention it here in case anyone might have a similar issue and might not have gotten the same letter or thought about it in conjunction with a CGM.

I have the applicator from my current sensor right here. That little silvery thing in the upper right? It attracts metal.

Tandem did warn me that I have to look for a G7 where the label number is underlined. Earlier G7 sensors aren’t compatible with the pump. So it’s possible you’re using an older applicator.

But here’s mine holding up a sewing needle.

That is unquestionably a magnet.

You’re talking about the hollow plastic post inside the screw cap. I’m pretty sure that’s a needle guard.

Regardless, there is definitely a magnet in the applicator, so my point stands. That magnet is there for a reason, which proves that the transmitter has at least some ferromagnetic parts, which means a magnet could potentially interfere with its operation.

Just like my sensor. Got a better look at the applicator and the sensor.

We were both wrong. The “finger” @joe mentioned is nothing to do with sensor startup or a needle guard. The needle is off to the side, and the center of the sensor, where it’s pressing, is hard plastic with no button. The plastic post is just holding the spring-loaded sensor in place during transportation.