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Medtronic 640 low suspend queries

catapillar

Well-Known Member
Messages
3,390
Location
UK
Type of diabetes
Type 1
Treatment type
Insulin
Somewhat unexpectedly, I have come home from the hospital today with a new pump. After rather too many ambulance call outs for severe hypos, and my trust being alarmingly keen to get me on the waiting list for a transplant they have decided an NHS funded CGM with predictive low suspend insulin pump is worth a try.

I won the prize for most number of medical devices attached to me this morning: a turned off omnipod, a dexcom sensor; new Medtronic pump and; enlite sensor. Now I have tubes, interesting.

So I've experience a low suspend already. But it stopped for about two hours. How does it decide to come back on? I don't understand what it's making its decisions on. If it predicts me going low but I've treated it is it going to know I'm fine & give me back the insulin? And then I went high after, because I spent 2 hours without any insulin, which seems blindingly obvious - hopefully not literally.

Can anyone help with how the 640 works - when it suspends insulin what needs to be happening for insulin delivery to resume? @tim2000s do you use a 640, can you give a girl a clue?
 
Hey @catapillar bet that was a surprise for you today then I use the 640g but don't have the sensor, however my understanding is that the 2 hour suspension period is based on a preset that takes into account that 2 hours is the recovery time period for a low blood glucose, I believe you can change the alert settings though so that you can 'alert before low' which will enable you to treat before going low and potentially stopping the 2 hour suspension. The help team at Medtronic are great so give them a call after 9am tomorrow and speak to the uk team and see how you can tailor the alert I am fairly certain that you can adjust to suit. A very smart piece of kit so I hope this helps you manage your hypos better, I would be keen to see how you get on
 
If I'm dancing or exercising in some other way, I'll leave the pump suspended and make sure I eat something (usually jelly babies). If I'm not doing very much, I eat something and stop the suspension but make sure I keep an eye on my BG, just in case.

When the pump alerts you, make sure you test, as sometimes it suspends when the BG is well above the cut off point (once my BG was 8.2!).

If your BG is dropping rapidly, 1, 2 or 3 arrows pointing downwards appear and you'll be alerted that you're going low. With your history, I'd test and eat. Trial and error will tell you how much or how little to eat. With 3 arrows, I leave the pump suspended till my BG starts rising then switch it back on.

I find that nights are the worst as I fall back to sleep, after eating, and tend to leave the pump suspended (to be on the safe side). If it's off for two hours, I go high later. I just correct and moan about the blasted diabetes, but that's life.

I don't know how the pump decides to switch back on again. Obviously it's the BG reading but it seems so variable (with me) that I just keep an eye on it and when my BG has reached a good level, I switch back on. However, sometimes I forget and my BG can be around 10 with 3 rising arrows, and it's still suspended.
 
Hi @catapillar - this will hopefully give you some idea of how it works. The detail is:

According to page 159 of the 640G User Manual, the conditions at which Smartguard kicks in are:
  • Your Sensor Glucose (SG) value is at or within 3.9 mmol/L above your low limit.
  • Your SG is predicted to reach or fall below a level that is 1.1 mmol/L above your low limit within approximately 30 minutes.
After the minimum 30-minute suspend time, basal insulin delivery will automatically resume if the following conditions are met:
  • Your SG is at least 1.1 mmol/L above your low limit.
  • Your SG is estimated to be more than 2.2 mmol/L above your low limit within 30 minutes.
The key is the level at which you set your "Low" value, given the way this operates.

So as an example, let's say you have set your low limit at 4.5 mmol/l.
  • As soon as your Sensor Glucose (SG) is between 4.5 and 8.4, the system is watching out for your drop rate.
  • If your drop rate is expected to take your SG level to 5.6 mmol/l within the next 30 mins, it uses this as a trigger to suspend insulin. (checked every five mins with sensor data)
  • You are now suspended for 30 mins.
  • After 30 mins, it checks your SG level.
    • If you are less than 5.6 mmol/l, you remain suspended.
    • If you are above 5.6 mmol/l, but are predicted to remain below 6.7 mmol/l in 30 mins, you remain suspended until either:
      • Two hours is up; or
      • Your predicted glucose level in 30 mins is more than 6.7 mmol/l (checked every five mins with sensor data)
Depending on the control you want to achieve, you will set your "Low" value in different places. I have Hypo awareness, so used to set my daytime low value at 3.8 mmol/l, knowing that it would predict I was heading low as we went through the 5s and 6s. Overnight, I found that I needed to set the "Low" value to 2.8 to avoid waking up in the 9s, as I found that I suspended quite frequently overnight. Opposite of what you might expect, I didn't have a lot of overnight lows with such a low setting.

It's quite a blunt instrument but you can learn to tune it and accustom your behaviour to working with it. The key thing for you when treating is to look at how much you will need to treat. The key difference when using something that suspends insulin versus traditional methods of dealing with lows is that by the time you are aware (unless you are using the alarms), it has usually already suspended insulin for a period of time, so the amount of CHO you need to treat a hypo is substantially lower than that needed in your pre-SmartGuard days.

For example, for me using OpenAPS, which has similar functionality, I rarely treat anything heading hypo as a result of basal with more than 4g carbs due to the insulin suspend functionality. If it's a result of mis-calculated bolusing then that's a different matter, and requires more thought.

Hope that helps. If you have any questions, just shout me!
 
Thank you @dancer and @tim2000s thats really helpful.

I think I've calmed down from my desire to microwave the pump this morning having woken up at 14.9 having had no insulin from midnight to 2 and again from 2:40 to 3:40. My low is set at 3.4 and I don't think in reality I was under 8 all night long. The last time I had no insulin all night long I couldn't do coherent thinking to treat it so I ended up in dka. This is not a promising start for me.

I think the sensor might just need a bit of settling in. And I need to adjust my low and tell it to warn me before it suspends so I can test to see whether it really needs to.
 
One other thing I'd say in relation to the Enlites is that you really, really need to pre-soak them. i.e. you need to insert the new one and give it 24 hours to settle down prior to plugging in the transmitter. Having said that, if you use this technique, I've found it works really well.

The other thing I found with the Enlites was that using my arms proved far more accurate and long-lifed than using my abdomen.

catapillar said:
And I need to adjust my low and tell it to warn me before it suspends so I can test to see whether it really needs to.
Click to expand...

Just a word of caution on this one. What you'll probably find is that you'll see it suspending at 7-7.3, which is fine based on its predictions, and it is doing the right thing. Use the alarm to keep an eye on how it works at first, and watch the trajectory after it suspends, then decide whether you think it was doing the right thing. When I back fitted the sensor data to my suspends over a period of a number of days, it was making the right decision based on its algorithm.
 
Ive managed to kill my second sensor. I left it in 24 hours before hooking up the transmitter. It seemed to be fairly accurate through Thursday. But last night it was telling me I was low when finger pricks were telling me I was 10+ it suspended insulin deliver for a while. It demanded a calibration at 5 o'clock in the morning, after having woken me up two or three times through the nigh with false alarms, and I unthinkingly let it calibrate with a BG of 9.7 when it was showing 3 or 4. The calibration wasn't accepted and now the sensor won't start up again.

When I did a very similar thing on Tuesday morning (after waking up basically ketonic when it suspended insulin when I was 10+) I spent Tuesday trying to get some more life out of the sensor with no luck. I continued with no active CGM on Wednesday and had a severe hypo and paramedic attendance, which was lovely. Well, I mean, I was concious and able to eat so could probably have managed to treat it without an ambulance had I just been able to keep my head up and get the dextrose tablets in my mouth but when I got round to asking for help a blood sugar test said it was less than 1.1 and too low to read so that freaks everyone out and results in a 999.

So, I will try and site another sensor, leave it 24 hours to start it up. @tim2000s what are the rules I'm supposed to be following to actually keep the sensor going for at least the 6 days? Should I be telling Medtronic about the sensor failures? I'm not at all sure about who is paying for these sensors, as far as I know I haven't had an IFR and my CCG is fairly resistant to funding CGM.

I've just had one flood of tears at 5am when I realised I'd done in the sensor. The low suspend thing is supposed to be the thing I'm trying so that I don't have to go on the transplant list. I've been told I have three options: 1) do nothing, but they think I'm at high risk or death/brain damage from severe hypos; 2) have a pancreas transplant, which has a2% mortality risk; or 3) have an islet cell transplant, which doesn't result in insulin independence but gives you what's basically a second honeymoon and helps out with the hormones to restore hypo awareness. Ive been advised by Kings that the other option is the hypo awareness restoration course, which is CBT, but before I can be recruited for the clinical trial for that I need to try the 640. I seriously hate it at this present moment in time, I feel like it's so inaccurate it's just going to kill me with a lack of insulin first, I don't cope well with being hyper, I'm not a fully functioning human in double figures. I can't be doing with the idea that I'm going to wake up every morning hyper because it's stopped insulin overnight. I just can't be living like that.
 
@catapillar I'm sorry you're having these problems.

You should have told Medtronic about the sensors failing . . . but they would tell you not to calibrate when there is such a big difference between your tested BG and the sensor's reading. (They would still replace the sensor, though.)

Once calibration has failed twice, you can't restart the sensor. You might be able to start it as a new sensor but the transmitter has to be recharged first. This means you have to, very carefully, remove the overtape from the transmitter, making sure you don't pull on the sensor. I found that cutting was better than pulling.

Were you told to insert the sensor 24 hours before connecting? I tried overnight but still found the first day's readings were often far out from the actual BGs. Sometimes I have great readings on the first day but often I have to switch off the sensor for a couple of hours when BGs and sensor readings are too far out.

I hope this helps a little bit.
 
Thanks @dancer thats a good tip, I'll try just turning it off just when it seems way out. I tried disconnecting the transmitter last time and it still wouldn't start again.

Will hope it all goes smoothly tomorrow. Third time lucky I suppose.
 
catapillar said:
Thanks @dancer thats a good tip, I'll try just turning it off just when it seems way out. I tried disconnecting the transmitter last time and it still wouldn't start again.

Will hope it all goes smoothly tomorrow. Third time lucky I suppose.
Click to expand...
You said you tried disconnecting the transmitter, did you charge it too?

It can be worrying having to switch off the sensor but it usually does work OK when switched on again a couple of hours later.

I hope all goes well for you tomorrow.
 
There is a 5th option - which i have done several times now - raise your control , with your doctor's agreement , so you never, or virtually never, go low for a period of months - not pleasant, and it may mean waking over 10 most mornings, but it does not put the HbA1c into more than 7.5%, doctors are happy, and it does, for me, work reasonably well, though one has to work at it, at least if one does not have a monitor, (i have never used one with a pump) one may have to do even more tests and aim for target of average of 8.8- 9.8 while doing it. It did mean , i found, a lot of days when i had to eat at unusual times, or hardly eat at all some days and eat more other days, as my rule was never eat on over 8.5, and my insulin needs are not very predictable. Health changes have forced me to do this recently again, and it does work, though unawareness can come back with even a few hypos. I have had to accept that i keep the HbA1c up more than i did once upon a time, just to keep hypos manageable. I hope things sort for you on the pump with monitor, mentioning this way in case you may need it later
 
@catapillar Where are you putting the sensors? I found them terrible on the abdomen and wear them on my arms, where the Libre suggests you use them. They were far more effective for me there.When I put enlites on my abdomen, the average age was 3 days before they stopped working.

Always report failed sensors to Medtronic. They replace them, and they need to know.

In terms of restarting them, I used the odd-shaped tape the Medtronic provides to tape with the hole around the sensor head, and then another piece with the hole around the tail tag that goes over the transmitter. Then I'd put a piece of opsite over the senor head as well. Once I'd attached the transmitter, I used the tail on it, then yet another piece of opsite over the transmitter.

When restarting the sensor, I'd cut the opsite, remove the tail tag and put it on to recharge, then before reapplying and restarting the sensor by using "Start new sensor" on the 640G, I removed the old tape, plugged it in and then applied another piece of opsite. All one handed and sometimes left handed (I'm RH). You learn dexterity when you have the sensors in your arms...
 
@tim2000s the first 2 sensors were in my abdomen. I've put this one in my arm, it took me flipping ages to get the needle out after and I'm not sure the tape is very well placed, but its behaving for now.
 
I use the 640g with the enlite sensor and have to say the low suspend did my head in. Like you it would suspend and I would wake up sky high so I switched it off. I now use the alert before low alarm and suspend on low. I wear my sensor on my arm wearing on my stomach guarantees it fails within 24 hrs. It will only kick back on after being in low suspend if it detects your blood sugar rising at a certain rate which normally after being suspended for two hours is too late and the rise is too much. You can restart your basal at any time during the suspend. Are the alarms waking you up?? When I had low suspend switched on the alarms would always wake me up and I'd check my blood sugar and if low correct with dextrose tabs wait ten mins or so and then switch my basal back on, it sometimes would suspend when I wasn't low at all or even close to being low.
 
Hi @AmandaD , if you use the "Suspend before low" functionality, it's not supposed to suspend when low, but before then, and not necessarily when you are close to being low either. It looks as the rate at which your glucose level is dropping and makes a decision based on current glucose level and that.
 
AmandaD said:
Are the alarms waking you up??
Click to expand...

Yeah it's difficult to sleep through something buzzing on your belly. Which is good cos I'll often sleep through a dexcom alarm. But it's waking me up for no good reason. So I'm not sleeping well with 640.

My third sensor failed. I'd put it on my arm. I gave it 24 hrs to settle in and calibrated 3-4 times a day. It was consistently reading lower than I was, so I was resuming basal. I went to calibrate before bed. It said I was 2.4, I was 4.1 and I wasn't moving that much cos I was 4.8 about 40 minutes before. It didn't accept calibration. I turned it off and back on, wouldn't work. I turned it off overnight, wouldn't work. I had a fight to take the transmitter out, charge, reconnect and it worked - for four hours. God knows how it manages to lose signal when it's cannulated to me, but it did, then it told me to changes sensor. When I took it out the sensor was significantly bent.

It's driving me insane, so I'm having a break. I've got my pod (so much more comfortable and I can wear a dress) and my dexcom back on. I'll try again next week.

Thanks for posting @AmandaD
 
Sounds as though you and the Enlites don't get on @catapillar - unfortunately that's something that happens with some people.
 
tim2000s said:
Sounds as though you and the Enlites don't get on @catapillar - unfortunately that's something that happens with some people.
Click to expand...

Yeah that's what I'm starting to think, maybe my body just doesn't like the enlites? But I'll have to try it again to see. I might have to find my determination first though!
 
hiya @tim2000s yeah I know that it just jumped the gun one too many times for me. It was actually my consultant that suggested switching it off and turning the other alarms on. He figured I was dipping the pump was suspending then my blood sugar was climbing as a result of the suspend, he felt that I'd dip and come back up on my own and he was right. He said the other alarms would wake me anyway if I went too low and after I switched it off I looked back at my cgm reading and if I did go low it was never lower than 3.9 and it would rise soon after anyway. I have shocking dawn phenomenon anyway so the rise as a result of the suspend was just too much on top of the DP rise. I now hover between 4.4 and 5.6 all night.
@catapillar the enlite will only allow you to recalibrate twice before it says change sensor. I'd ring medtronic and get replacement sensors you might have a faulty batch. I need someone to remove the needle after I insert otherwise I just pull the whole thing off I can't get it out one handed. I insert mine, cover the top of it with the tape provided, leave it sitting there twenty mins or so until the transmitter is charged. Attach transmitter and cover that again with the tape provided then cover the whole lot with IV3000 hand clear dressing. I can get 6 days out of my sensor on my arm, abdomen 2 max if I'm lucky. I clip my pump to the top of my pjs so its near my arm when I'm asleep and I don't get any of the lost sensor errors anymore. I've also read something about compression lows if you are lying on the sensor but I know nothing about them.I've been using the enlite sensor now 6 years and got the new one at my last pump upgrade.
 
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