Posted by on Saturday, 30 December 2017

CGM, diabetes time travel, and lessons learned from go-karting

Image by 'aurorasognatrice' used under cc.
2017 is hurtling to a close, and despite my giddy optimism about having 'loads of time' over the festive break to do all sorts of things that I don't generally get around to, the days have passed in a blur of hopelessly guestimated carbs, fun, friends, family and alcoholic excess. Consequently I am once again hastily cobbling together a round-up of the year type post - you lucky lot.

Almost exactly 12 months ago I was placing my order for a transmitter and first box of sensors for my MM640G insulin pump. I'd trialled the system over the summer of 2015, and I have always opted for Medtronic pumps with the vague notion of possibly, some day, self-funding CGM - but this was the first time our family finances had permitted it. I'd been using Freestyle Libre sensors intermittently for a few years (which you can use sporadically without the additional £500 for a transmitter), so I was interested to see how occasional SmartGuard coverage worked out for me.

In the end 2017 turns out to have been by far my most sensor-filled year. I was invited to trial Medtronic's Guardian Connect in April, and was unexpectedly and very generously gifted some short-dated sensors by someone who was switching systems and could no longer use them.

I always try to get the maximum use out of every self-funded sensor I insert, and I am fortunate to be able to restart almost all of them for at least another 6 days while retaining good performance. This almost halves the cost - or more accurately for me, doubles the sensor coverage. I had hoped to spread 10 'stretched' sensors (approx £500-worth) across the year to give me somewhat less than 50% coverage, but in the end, have been able to use them continually for quite a number of months which has been a very interesting contrast to my usual pancreas impersonation guesswork. It's interesting to reflect on the changes I've noticed myself making to day-to-day management decisions, and how it has felt as an experience. Here are a few basics:
  • On the whole it has felt far easier to live with diabetes this year.
  • I've not done any complex analysis of BG results, but my basic monthly spreadsheet analysis (nerd alert) shows significantly better results.
  • My A1c has fallen by 7mmol/mol (0.5%) and my hypoglycaemia has dropped significantly
  • Sustained reduction in hypoglycaemia has really improved the reliability and timing of my warning signs.
  • For the most part I seem to be operating with around 80-85% of results in range (4-9mmol/L) - even over Christmas. This is ridiculous.
  • On average I've only been getting 1-2% of results below 3.9mmol/L, nocturnal hypoglycaemia has been almost completely eradicated and I am having days and sometimes weeks at a time with all but no readings below 4.0.
  • These are not results I can achieve without continuous data, not matter how hard I try.
  • Even with the benefit of Freestyle Libre these are results I find it impossible to achieve. The alarms of full CGM provide me with significant added benefit, especially for catching lows.
  • Occasionally life with CGM has been rage-inducingly frustrating, and alarms have sometimes driven me to distraction.
  • I've had a few duff sensors and made some very poor choices based on inaccurate sensor data.
  • Additionally, SmartGuard is a bit of a liability with an inaccurate or under-performing sensor, sometimes sending me into double figures with a cancelled basal (and sometimes half of a slowly-delivered bolus!) when I would have been fine if left well alone.
  • SmartGuard is amazing for me, but very often I can't resist overruling it, ending it early and/or adding some carbs. Sometime this works better, sometimes I suspect I create more problems for myself than is strictly necessary 
  • Additional data is a significant help to me day-to-day. I've come to rely on it and feel quite lost without it, but there are times when some of the subtle details of life with CGM have created their own challenges - which leads me to...
CGM and diabetes time travel
I've always been one for a thinly stretched analogy. I can't help myself. There are two coming up... You have been warned.

With absolutely no apologies for the shameless 'Christmas Dr Who' reference, I've also been thinking quite a lot this year about the diabetes time travel that you get involved in when tinkering with continuous data. I've considered this before in terms of the repeated half hours you can spend with diabetes waiting for various management decisions you have made to start working - periods of waiting which can seem interminable. With more time spent in CGM-land this year I've noticed additional time travelling shenanigans with the lag between 'sensor glucose' read via interstitial fluid and actual 'what's happening now' blood glucose information.

This was brought more keenly into focus with my brief dalliance with the faster-acting Fiasp. An insulin surrounded by feverish hype of very rapid action - which sadly for me rather failed to live up to expectations. But the promise of faster acting doses has occasionally made me feel the sluggishness of Novo-not-very-Rapid all the more keenly.

Mostly I find 'sensor lag' is barely noticeable, but with a whiff of irony, it is when my BG is on the low side and I'd really appreciate accurate information that this 'time travel' is most clearly noticed. Looking at a Libre or Enlite trace at those times, shows you what was happening something like 10 or 15 minutes ago. And any 'rapid' carbs you take to bring up those low levels, or turn-around a dip towards hypoglycaemia won't change your blood glucose for 10 or 15 minutes, and may not show on the eagerly-watched line for a further 10 or 15 minutes after that. More than enough time to double-treat, only to watch your levels climb into double figures a little while later.

In just the same way, when you have a trace to watch, there is a powerful urge to see a high-and-rising BG trace turn around. But correction doses for me are unlikely to show any noticeable effect before 60 minutes have passed (unless I add increased activity into the mix) - plus the mandatory 10-15 minutes, of course. And at each of these moments the graphed time-travel of results, and interminably upward direction of travel gives few clues as to when it is 'just about' to level, or begin to dive downwards. Threepio proudly suggests 'insulin on board' from which you might think I could make an educated guess (and sometimes I do luckily seem to drag some precious clues) but all too often I can find my IOB dwindling away to nothing, coping only with mis-guessed carbs, rather than the elevated BG I had hoped to squash. Other times I can bear it no longer and wade in with an additional dose, only to see my BG trace drop off a cliff and plunge downwards - awash with both insulin and various types of carbs. Which reminds me...

CGM and lessons learned from go-karting
I have only been go-karting three times I think. By which I mean the crash-helmeted-boiler-suited-whiff-of-2-stroke-engines style go-karting rather than the sliding-down-a-hill-in-a-fruit-box-with-pram-wheels-bolted-on style. I don't think it's an exaggeration to say that I'm absolutely terrible at it. I was reminded of my go-karting prowess when thinking about some of my... erm... more questionable diabetes decisions in response to a more frequent CGM data-feed. I suspect I am not the only one who has fallen foul of the double-dose and/or double-treat temptations - and for all the benefits of all that extra information, it is unmistakeably one of the risks.

The very first time I sat in a go kart, in a dimly lit, oily, industrial shed on the outskirts of our city, my driving style was essentially binary. The accelerator was either fully down or entirely untouched. The steering wheel locked at either edge or dead centre. Brakes were applied with sledgehammer-like gracelessness. As a result I kangarooed around the indoor circuit, making full use of the amply-supplied tyre walls and doughnuting my beleagured kart in furious circles. I proceeded at lightning speed from one collision to another and made very little effective progress around the twists and turns of the circuit.

This is pretty much the way I drive my diabetes when things are not going well. Frustrated by apparent lack of action of more reasonable measures I heftily over-correct with hugely inflated insulin doses or swigs of Lucozade. Lurching and stumbling from high to hypo and back again. Crash! Clonk! Screech! Everything becomes overblown and chaotic.

The second time I went karting was every bit as 'successful' as the first, but I had something of a lightbulb moment on the third occasion - which was at an outdoor circuit. For whatever reason, this time I adopted a more subtle approach. The accelerator was rapidly pressed full down at the start, then backed off in time for the first corner... rather than stamping the brakes I found myself making little feathered dabs. Steering was altogether more considered. Confidence grew. Speeds into tricky corners increased, a late firm braking followed by a hard turn of the wheel and full throttle at the mid-point of the turn allowed me to power-slide out of the corner. I was still making strong adjustments in some circumstances, but more often my choices were much more subtle, more measured.

This is what I see when my diabetes management is more successful. It is when I am able to make smaller adjustments that I do better. Multiple big overlapping doses and rapid-carb 'rescues' can leave me in a flat spin and going nowhere. Smaller tweaks, spaced further apart are often significantly more successful. I have found this to be a really interesting and important thing to think about when Threepio is merrily warbling away. Those alerts can seem equally frantic, but I need to pause and consider my position on the 'circuit' of my day. Can I just coast through this corner without stamping on the brakes (adding insulin) knowing that the turn of the wheel or dab on accelerator I've already made is enough, or is this the devious hairpin and do I need full-lock and firm braking before powering-on with additional carbs to make the turn.

In general terms, when I notice that I am oversteering and stamping on the brakes and accelerator of my diabetes managment, I am trying to remind myself to make a couple of slower laps and build up to speed again more gradually with more gentle adjustments.

Widening the access to continuous data?
I was delighted to be invited by Abbott to attend DxAmsterdam in July, and then in September the eagerly awaited news was released that Libre was to be placed on the NHS tariff and could theoretically be made available on prescription, subject to local CCG decision-making (and perhaos an emerging postcode lottery). Abbott's real-world data, shared in Amsterdam, backs up my own experience of access to continuous data - that the more information I have on which to base my guesswork, the better things tend to go for me.

Diabetes still has the capacity to be hugely annoying of course, but for me - more data certainly leads to better results. Continuous data is not without its challenges, and it will be vital for people living with diabetes to be given appropriate support and help in order to make best use of the information and avoid the pitfalls. Both in terms of their support from their clinic and also perhaps, those who have made the mistakes before them and can share their experiences. It will be really interesting to see what effect wider access to these technologies delivers as access to Freestyle Libre and CGM increases in the years to come.

It remains to be seen quite how much life my transmitter has left in it. They are warrantied for just 12 months. I will continue to use Enlite sensors for as long as I can, especially since my CCG seem rather reluctant to take any decisions on the finding of any kind of sensors for anyone - however great the need. I would imagine I would be very far down any list they eventually decided to draw up. After that I'm not sure if I will revert to Freestyle Libre, spring for another Guardian transmitter or take a continuous-data break.

Wishing you all a tip-top 2018. And thanks as always for reading.


  1. Good review! I liked the karting analogy - sometimes it does feel like we're bashing around the course over and under-correcting!

  2. Thanks for sharing Mike, HNY to you all

  3. Thank you Mike for this entertaining and informative article. I was given a freestyle libre reader and a 14 day CGM sensor before Christmas but I hadn't discovered the art of subtlety of treatment then and to be honest, what with Christmas, family and flu, well it all rather went to pot so I'm probably going to buy another sensor and give it another try. Bearing in mind your go-karting analogy; as someone who also has a tendency to lurch from extreme highs to extreme lows, I will make a conscious effort not to overtreat either status. (This was clearly depicted in the erratic diagrams that emerged when I uploaded my results). Anyway, you seem to have things pretty well under control now so I hope I can use your insight to improve my readings.

    1. Thank you so much for your feedback Sally. If it is any encouragement, I had a couple of sensors in my initial trial which I used more or less back-to-back. Initially results were a bit chaotic, but by the third of the 4 weeks I was making good discoveries and was able to tame some of the excesses.

      Since then I've generally used sensors intermittently as a 'reset' or to provide extra information over less predictable times food-wise (Christmas, holiday etc). Once I was more practised I found (more often than not) that I saw significant improvements in the second of a sensor's two weeks as my adjustments to basal evened things out and allowed my meal doses/corrections to work a little better.

      Good luck with your next sensor(s) and I hope you see a real return on your investment of both time/effort and cash.

      Thanks for reading!