Dexcom G4 fails when blood sugar changes rapidly

[Platinum]

When my blood sugar falls or rises very quickly, my G4 sometimes stops working for at least two and usually four or five hours and displays the ??? or a timer symbol. Does this happen to anyone else?

The chart below is typical of what happens (If I do any exercise at all my BM falls very rapidly irrespective of how I set my pump or what glucose I consume - When I stop the exercise my BM rises just as rapidly and can be difficult to control).

 

[Chas C]

Have you tried drinking a large glass of water when it appears to stop working, I often find it happens to me when I'm not drinking enough.

Over the Xmas break mine stopped around 11:30am even though I'd drunk maybe nearly a litre of tea/coffee by that time but last drink was at least 2 hrs earlier. Had large glass of water and within 5 mins all was good again ?

 

[tim2000s]

@Chas C - The large glass of water thing is actually an urban myth relating to the term "Hydration of the sensor", which is about it getting enough fluid to start registering values. There is no way that water imbibed into the stomach can physiologically have a noticeable effect on water concentration in the ISF within the five minute period you describe. Whilst it looks like a great theory it is sadly just not true!

 

[catapillar]

When my blood sugar falls or rises very quickly, my G4 sometimes stops working for at least two and usually four or five hours and displays the ??? or a timer symbol. Does this happen to anyone else?

The chart below is typical of what happens (If I do any exercise at all my BM falls very rapidly irrespective of how I set my pump or what glucose I consume - When I stop the exercise my BM rises just as rapidly and can be difficult to control).

If my sensor has been in for a while (really anything over 5 days, if it's not brand new in) it can struggle to keep up with blood sugar changes during exercise. Definitely if it is an old sensor (14 days plus) it's likely to give up and just give me ??? From the second I step on the treadmill, which is helpful. But most of the time it will cope alright with exercise.

I think it just confuses it - I think it changes the readings it's getting from under you skin into a number that's akin to a blood sugar reading and I think that gives it an expectation of where it's going. And then suddenly it's getting numbers that are completely different from what it is expecting, so it just gives up and has a little rest. Mine usually wakes up again when I've given it a blood sugar entry when I'm a bit more stable.

 

[Platinum]

I just noticed that my CGM chart did not come out in the post – Sorry!

Thanks for the replies. I was wondering along the lines of the blood sugar change being too fast as well.

If I plan exercise, I bolus around half of my usual, and have a couple of bottles of GlucoJuice just before I start. This gives me a fairly high BM before I start, but this high BM of say 13mmol/l will reduce to a hypo in about 10-15 minutes.

By exercise I mean trimming the hedge, sweeping up leaves in the garden. Not anything to raise a sweat over.

The only ‘fix’ for me is not to eat for at least six hours before any exercise.

 

[Chas C]

@Chas C - The large glass of water thing is actually an urban myth relating to the term "Hydration of the sensor", which is about it getting enough fluid to start registering values. There is no way that water imbibed into the stomach can physiologically have a noticeable effect on water concentration in the ISF within the five minute period you describe. Whilst it looks like a great theory it is sadly just not true!

Hi Tim - its not an urban myth as you suggest, it works for me and has done many times.

I have had days where my fluid intake has been lower and in most cases my Dexcom stops working, within 5-10 mins of taking on board water my Dexcom starts working again. I have lost count the times I've done this and every time its worked for me.

 

[Chas C]

Hi Tim - its not an urban myth as you suggest, it works for me and has done many times.

I have had days where my fluid intake has been lower and in most cases my Dexcom stops working, within 5-10 mins of taking on board water my Dexcom starts working again. I have lost count the times I've done this and every time its worked for me.

A study by researchers at the University of Montreal, published online in the European Journal of Applied Physiology, takes a very detailed look at the kinetics of water absorption and offers some answers.

The study gave 36 volunteers 300 mL of ordinary bottled water, “labelled” with deuterium (an isotope of hydrogen than contains a proton and a neutron instead of just a proton) to allow the researchers to track how much of that specific gulp of water was found at different places in the body. They found that the water started showing up in the bloodstream within five minutes; half of the water was absorbed in 11-13 minutes; and it was completely absorbed in 75-120 minutes.

So not an urban myth then @tim2000s