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| Medtronic MM780G and Simplera Sensors (Apple watch not included) |
Hello. It’s been a while!
The embryonic posts I had in my mind about living with the Tandem tSlim never seemed to manage to make it to the top of the ‘to do’ pile, and remain unwritten - which I'm sure was a relief all round. But there’s nothing quite like a deadline to spur a (largely ex-) graphic designer into action. And tomorrow I am awaiting the delivery of my new insulin pump, as the warranty on my Tandem tSlim has elapsed. So it felt like a long overdue blog post could no longer be avoided.
Interestingly the ‘new’ pump isn’t particularly new at all. It’s the pump I rejected in favour of the tSlim 4 years ago. This might surprise some people. So why am I not sticking with the tSlim? Or joining the ever-growing horde of podders? But no, for me it’s the venerable MM780G, but with the fancy new Simplera sensors.
So Long tSlim
Confusion about my choice of ‘new’ (old) pump might be even more confusing because I have repeatedly said that I’ve never had better results than with the tSlim. My overnight readings in particular have been spectacularly good, very stable, and never required the alarm/calibration acrobatics that plagued my last days with my MM640G. Automated night mode suited me brilliantly, and I just expect to wake between 5.5-6.5mmol/L every day.
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| Non-shabby 90 Day Results |
Control IQ added approximately 10-15% to my average ‘time in range’ which I choose to set 3.9-9.0mmol/L. My previous general 70-80% has become more like 80-95% most days. This is pretty spectacular with something as fickle, contrary, and annoying as Type 1 Diabetes.
Dexcom G6 mostly tracks my BG levels brilliantly. While I was self-funding (for approx 3 out of my 4 tSlim years) I was able to stretch most sensors to run for 20 days with a viable and solid flow of data, that I was confident to use for most corrections, alerts, and bolus calculations.
So in many ways, I am really happy with the system, and have certainly seen significant improvements from running a hybrid closed loop system. I’d really not want to go back to a pump which isn’t integrated with a sensor and making adjustments.
If anyone is considering the tSlim, I’d say go for it. It’s a very smart-looking and smart-behaving insulin pump. And it might really suit you well.
So why the switch?
Good question! With diabetes gadgets and gizmos over the years I’ve found that the devil is very much in the teeny tiny details. And that even something that’s brilliant, and well regarded, can somehow just not ‘click’ with you and your particular diabetes’ foibles.
This seems to be doubly true with algorithms.
An algorithm is based on a way they expect a person’s diabetes to behave. And how much of an adjustment that person might need to steer things in the right direction in any given set of circumstances. Your own individual diabetes may, of course, have other ideas. But commercial systems being what they are, they don’t really want to offer you much in the way of adjustment or personalisation. It is what it is.
Pretty soon after starting in the tSlim (with only Basal IQ at that stage) I observed that their predictive low-glucose suspend acted much later, and switched off much earlier than the one I’d been using on the MM640G for several years. There were a gradually phased series of basal reductions before a full suspend (really my body needs a full shut-off from the start), and the insulin resumed very soon after an up-tick in sensor values was seen. This was good in the sense that I didn’t have any of those occasional teeth-grindingly frustrating high BG alerts following an over-long suspend. But it was a bit rubbish, on balance, because only the most gentle downward-drifts were caught in time for me. Even when I activated ‘Exercise Mode’ for such strenuous exertion as wandering round to the shops.
In the old days I’d have set a Temporary Basal Rate to start things off early. But Hybrid Closed Loops don’t let your set TBRs, because... well... they are supposed to be doing all that stuff for you.
I experimented with setting essentially a fake TBR basal profile of 0.1u/hr for the 24 hours and activating that at the start of dog walks and such... But then, inevitably, I’d forget to switch back when I got home, because TBRs had always just cancelled themselves after a set time. Following an update of the Control IQ software I was able to completely suspend the pump for a defined number of minutes after which it alerts to restart. This was OK, but for reasons I cannot really understand this also silences any alarms of impending hypo/dropping BGs the pump might helpfully provide if basal-suspend isn’t enough on its own, and levels are getting a bit close to the edge.
Dex lag and alarm fatigue
Initially I was blown away by how well the Dexcom G6 tracked my BG
levels. Whenever I did a ‘how are things going’ cross-check the results
between fingerstick (Contour XT) and Dexcom G6 were only ever a few
tenths of a mmol/L out. This gave me huge confidence. But at some stage
in the first year I observed that the problems I was having with the
late action of tSlim’s predictive low-glucose suspend were being
compounded by a distinct lag between capillary glucose and sensor
glucose. This isn’t news to me, and I understand exactly why this lag
exists, but Dexcom seemed more reluctant to respond to changing values
than any other sensor I had used. Almost as if part of it’s ability to
match capillary glucose so well when things were stable was bound
up in taking extra values and only updating sensor glucose every 5
minutes - perhaps it just waits until it's sure? For me Dexcom G6 is
almost always a whole 10 minutes behind moving glucose. And when a ‘this hasn’t worked’ Control IQ alert is happening only 15 minutes before levels dip below 4.0 (and
that ’15 minutes’ is what was happening 10 minutes ago) well... some of
my increased number of low-level hypos were easily explained. From 1%
below 4.0mmol/L to frequently more like 3 - 3.5% - still on target, but
I've worked hard to restore flagging hypo awareness and this really
can't help.
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| When is a 4.2 not a 4.2? When it's 10 minutes later |
Added to that there were challenges at the other end too. I’d get told that the basal suspend wasn’t enough and to take preventative action after I was already low, and then 10-15 minutes later be told that levels hadn’t recovered, which prompted me to re-treat. Only to then discover that actually that hypo-treatment had been enough, and that the double-treatment was now gleefully pushing me into the teens. Maybe 5-minute updates 10 minutes behind reality are OK for some people - but when I really need to know how things are moving at the sharp end of hypo-dodging, they were causing me frustration and treatment errors.
The upshot was that pretty early-on I had to take the up reins of hypo-dodging myself again. I set my ‘low alert’ at 5.2mmol/L because (10 minutes behind), that gave me enough time to take action if necessary - with a sensor reading 5.2 and dropping I could easily be low 4s when the alarm sounded and need some rapid glucose to steer away from the 3s. I had the alarm repeat at 30 minute intervals, so that I’d get a reminder to recheck to see any action I’d taken had worked.
But of course it might be that I was just pootling along in the 5s. Getting little warbly nags every 30 minutes. Which was quite annoying.
Even more annoying
But nothing like as annoying as the tSlim’s attempts to actively sabotage my hypo-dodging efforts. Alongside a rapid resumption of the basal profile, the tSlim has, on multiple occasions, delivered a mini-bolus just as my levels were returning to safety after a hypo treatment(!). For meal mis-calculations, or dose-timing errors it never seemed quite so enthusiastic, or effective, at turning around a rising BG, but getting another low alert in the high-4s on a dog walk or while gardening, having successfully treated the last one - and then finding out that it was the tSlim that had caused it with a completely unnecessary mini-bolus, was the inspiration behind some particularly florid and lively outpourings of language over the past 4 years. I asked my consultant whether they knew of workaround/setting to prevent this. Alas none was available. So I had to hugely down-grade my correction factor during the likely hours of evening dog walk, which of course means Control IQ can’t work ‘properly’ during those times when dog walks have happened at other times. And again, setting or not setting ‘Exercise’ mode doesn’t seem to be the fix.
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| The hollow squares are tSlim autoboluses |
Better results, but more effort
So yes, I have had better results, and the tSlim has handled many things really well for me. But the alarm fatigue has been pretty tough going. I’ve had a much higher numbers of non-severe hypos than I was used to on the MM640G, and I really miss the discovery that my pump has fixed something for me after the fact, quietly, in the background, with no alarms or notifications required.
Hopes for the MM780G
It was the memory of weeks and weeks with no sub-4 numbers that got me wondering about returning to Medtronic, and giving their hybrid closed loop a try. The pump is the same format, and the chassis is still as clunky and grim as ever (though I’ll be glad to have a screen that’s visible in sunlight again - the tSlim is awful in daylight), but they have updated the software, so it's not exactly like going back in time 4 years.
Medtronic G3 sensors never worked well for me and needed frequent calibration, including overnight. I gather the G4s were significantly better, and I have high hopes for the new Simplera sensors that I’ll be starting on.
I know quite a few people on the MM780G, and almost without exception they seem to get on very well with it. I know there will be frustrations and annoyances - there always are. But I’m hopeful I may be able to experience some of the “spending less lime thinking about diabetes” that others mention. On the tSlim I think I’ve had to think more - constantly checking up on what it’s doing, and fixing some very silly decisions it was making from time to time.
I’ll let you know how I get on.
