This may be a new opening of an old wound. I have seen and heard of COMPRESSION LOWS rearing its ugly head this fall. I am trying to wrap my head around the term and what is happening in the body. Does this seem like a good description?
BACKGROUND: Compression lows are caused by the person’s body pressing against the mattress, pinning the CGM sensor/transmitter (CGM) between the person’s body and the mattress during sleep. First, the interstitial fluid (IF) is the fluid around body cells. Most of the time IF is exchanged with fluids in the blood vessels. During this exchange, IF glucose is enriched and cellular waste products are removed from the IF all over the body.
THE PROBLEM: When a person is in sound sleep and is mashing the CGM into the mattress, the IF is also mashed. It is this mashing or compressing of the IF that causes the IF not to exchange as it normally does. Since the cells around the CGM sensor wire continue to consume (eat) the glucose available in the compressed area around the sensor wire the glucose in the area drops.
OBSERVATION: It is this low reading in the CGM data is usually seen as a nearly level data graph and then a sudden drop of the glucose level. Because it is a low brought about by the pressure on the CGM, the term COMPRESSION LOW has been offered in pumping circles. Because the Compression Low is a low glucose only in the area of the CGM, a finger stick performed in response to a LOW alarm will show NORMAL. The variation between the finger stick and the CGM data leads to frustration and bewilderment, believing technology is the source of the error.
The next observation is the blood sugar measured by the CGM will return to a value near where the CGM line was before the drop in CGM value. The near level line, the drop & alarm, the finger stick of different reading, and the return to the near pre-alarm value is the full picture of the COMPRESSION LOW.
Ihi @987jaj yes, I think this sums it up. my only comment is this: if the CGM is supposed to indicate blood sugar, then the device, or the technology, IS the source of the error in a compression low. If you fully understand that IF is an analog, that the sensor in IF is accurately reading IF then the source of the error is the difference of the IF and your actual blood glucose. That would mean the device (the technology) is accurate but the IF analog is no longer proportional to blood sugar. Semantics? I think so but I’ve had a long week, doing battle with both my quality department and my technology department (not in the CGM industry, but in pharma) and this is about all the strength I have left. Cheers!
My comments J @987jaj tend to run a path similar to @Joe’s; not a device malfunction but rather the body “not delivering” substance that the CGM sensor needs to accurately perform. Put another way, insufficient IF [interstitial fluid] around the sensor wire, or IF that has for some reason been exhausted of glucose - must probably, that body muscles needed glucose feeding.
This CGM occurs [at least with Dexcom G6] for reasons other than compressing the sensor while with pressure while sleeping; at least in skinny guys like me during of following activities. I’ve had some really interesting conversations about this with technical people at Dexcom and at Tandem. Dehydration may be a cause for the sudden drop in IF glucose level.
An example: today as I completed my usual five mile morning walk, my CGM was reading a wonderful 108 mg/dl; this despite “Exercise Mode” which targets 140mg/dl being set on my t-Slim for two hours. Yes, I drank my usual 20 ozs. of Gatorade [not the 0 sugar stuff] while walking. I made my usual notations in my notebook, and began lunch preparations; did a 20 minute pre-eating bolus, set up my outside lunch station and saw my CGM reading at 84. Washed my hands, made lunch and before my sandwich finished toasting, my device was sounding “emergency” and CGM reading 54 mg/dl. The “glucose drop” from 108 to 54 took about 20 minutes - actually my glucose didn’t drop.
The G6 realizing something was wrong, ceased operation - “sensor error”, with no readings for 20 minutes; upon resumption of G6 readings, my BGL was displayed as 101 mg/dl. The glucose reading device did not malfunction, my body was the culprit.
On very rare occasions I’ve gotten a “sensor error” alert. I called Dexcom the first time after switching out my sensor, and had them send a replacement. They told me to wait next time before calling (I don’t recall how long of the top of my head) to see if it resolved, and the couple of times sense then I have, and it came back. I didn’t know why it didn’t but I’ll keep this in mind. Thanks!
Dorie @wadawabbit, there are other reasons for "sensor error " readings, and the display will read " — ". These are almost normal; when these readings are presebt, the Dexcom display, on phone or receiver, will tell you to wait three hours before calling Dexcom.
What iwas describing is a sudden dropping of readings, one distinguished from compression. I have documented for Dexcom research precipitous reading changes of more than 75 mg/dl in less than a 20 minute period. Thankfully, this only happens a couple of times a week.
Thank you. I’ve gotten those annoying "Wait 3 hour dashes a few times - usually less than 3 hours before I’m planning to go to bed unfortunately , so thankfully they’re rare. The possibility of dehydration is one I should keep an eye on as I don’t drink as much water as I should so that’s helpful to keep in mind as a possibility - one of many.
Actually J @987jaj you posted a Topic, with your good observation, that could be of interest and learning for many members/readers of this site. I found your presentation to be accurate and well-stated; what I added is another instance where the G6 [I don’t recall this happening with G5], with its 30 minute “anticipation/prediction” could cause apprehension for users.
I’m hoping to hear from others on this topic. Over the years, listening to others, I’ve heard instances of “one-size-fits-all” doesn’t apply to TypeOne.
Hi @987jaj
Thanks for writing about this. I’ve been on a Dexcom CGM for a year and a Tandem CIQ for 6 months. I’d noticed these deviations from steady state (constant, or sometimes uniform low slope), mostly taking place while I am asleep but occasionally while awake. When I have been awake I’ve checked my BG meter and as others have pointed out, found that the CGM “low” is a false positive. I was going to ask my CDE yesterday, but she anticipated and asked whether I’d seen this and named it.
Some background: This is not a source of worry for me, I check my meter before making treatment decisions. The only negative effect is that CIQ will turn basal off, so when the compression low episode is over there will be a slight rebound in CGM’s IF readings (and I assume in actual BG) and then CIQ corrects for it, which is clearly visible in the Tandem data (as a new user I am limited to one image per post).
Zooming in on the Compression Lows
Regarding IF, capillary glycemia, the delays and non-conservative transfers between them, and how to really calibrate, I am collecting my thoughts and will post here.
@climberT8 , your tight zoom in is actually so tight it is difficult to decipher. Attached is a tConnect image of a verified COMPRESSION LOW. Of note, the CL did have the CGM report a LOW, CIQ responded to the LOW by throttling insulin to zero for a period of time allowing the real glucose level to rocket upward. Once the CGM reassessed the environment, the value was elevated.
CIQ again in concert with the CGM throttled insulin up and started managing the elevation via increased basal as is expected with CIQ in SLEEP ACTIVITY (the Tandem term).
Once you learn to read the full image from tConnect as I do, you don’t even bother with a finger stick. I was taught well enough to read the CGM data line, I have not needed to do a finger stick in more than two years with endo’s blessing. Endo & other docs check CGM to lab glucose about every other month and everytime it is spot on.
Hope this helps… BTW, your graphic does need a key about what the various CL1, CL2, & CL3 represent.
, so thankfully they’re rare. The possibility of dehydration is one I should keep an eye on as I don’t drink as much water as I should so that’s helpful to keep in mind as a possibility - one of many.
