Wednesday, January 6, 2016

Frustration with Enlite

I just disabled all alarms and the SmartGuard feature of the pump.

I have great trouble getting the Enlite sensor to be accurate. Maybe it's just me, maybe the sensor finds my tissue hard to read, maybe I'm not calibrating it right, maybe there was something off in the manufacturing or transportation of the particular batch of sensors. The sensors just keep giving me numbers that are way off from what my glucose meter says.

At 10 am, when I woke up, the pump told me the sensor reads my glucoses at stable 3.8 mmol/l and the SmartGuard feature has been activated to save me from going too low. I did not feel low at all, so checked with the meter. It said 9.9 mmol/l. And 10.4 mmol/l when I measured again. And after washing my hands carefully, still 10.2 mmol/l. The real glucose level was clearly around 10 mmol/l. I dismissed the SmartGuard to resume the insulin flow, and injected some insulin to bring my glucoses down. I did not calibrate at this point, as I was sure the calibration that far from the sensor reading would be rejected by the transmitter. I felt a bit frustrated, as I thought the SmartGuard action of the night was likely the reason for the high level. It may also be that my glucose levels had really been low and then bounced back up due to my liver releasing some glucose into my bloodstream just before I woke up, so the sensor just did not have time to catch the change.

An hour later (at 11:12), just before breakfast, my meter told me I was at 6.9 mmol/l, so I bolused accordingly. Again I did not calibrate, as although the meter reading was now much closer to that of the sensor's (5.2 mmol/l), there was an downward arrow in display, so I knew my glucoses were still dropping, a bad time to calibrate. Shortly after, the pump buzzed and told me that insulin delivery had been stopped again, to save me from going too low. I needed to dismiss the SmartGuard again, as I knew I wasn't that low, and was currently eating, which would rather bring my glucoses up soon. In addition to that, it took me a while to find the amount of bolus insulin that had been injected (only 0.15 units -- the bolus delivery rate of the 640G is really, really slow!), and even longer to find the real amount that should have been injected.

While I can understand the logic the sensor and the pump used, and acknowledge I'm not yet familiar with the menu system and that's why it takes me time to get around and perform some actions, I became frustrated. It felt I was just fighting an enemy, rather than working together to treat me in the best possible way.

I have used the Dexcom G4 CGM for more than a year, on and off. Before that I occasionally got a CGM (either Dexcom or Medtronic one) from my clinic for a week. Throughout this time, I've gotten better results from the Dexcom. 90% of the time, it shows what I expect when calibrating it (that is, within 15% of the reading of my glucose meter). And 90% of the time it's off, it's easy for me to see, in retrospect, the point when it got off the track and also back on track. Either I calibrated when my glucose levels were changing rapidly, or I probably slept on it, causing the so called 'pressure low'.

With the Enlite, I have never gotten the same feeling. I have no idea why it behaves the way it does.

When searching the internet, I find I'm not the only one with these issues. See for instance the end part of this review:

I also had a short discussion about the issues in Twitter.

Anyway, for a couple of days, at least, I don't let the Enlite sensor interfere with my treatment. I keep wearing the sensor, and keep watching its readings. I hope I can better learn the ways it works, so we can work better together. I already got some advice from both a local representative and a peer support group:
  • Calibrate at least 3 times within first 5 hours after inserting the sensor.
  • Only calibrate, if bg/ISIG is above 0.14 and below 0.44, applies when bg is in mmol/l).
  • Pay attention to the insertion site.
  • Try inserting the sensor first, connecting the transmitter hours later.
I really want to learn to trust the sensor and the system. For me, the SmartGuard feature of the Medtronic Minimed 640G is a really promising step towards an artificial pancreas. A system that would eventually do all the micro management required to control my glucose levels for me. But there's no way I'm giving that responsibility to a system I don't fully trust and understand.

Finally, I ask you to remember that in this blog I share my experiences when and as I face them. I may be totally in love with the system next week.

Monday, January 4, 2016

Will I use the bolus calculator of the Medtronic Minimed 640G?

I have been using the Accu-Chek Spirit Combo pump system for five and a half years. I have been really happy with its bolus calculator feature.

When I first started pumping, I was offered a choice between Accu-Chek, Animas, and Medtronic pumps. I chose the Spirit Combo as it's meter could be used as a remote controller for the pump. This means whenever I measure my blood glucose, I can immediately also dose the right amount of insulin, without having to reach for another device. I still think this is a winning feature.

After having used the system for some time I came to appreciate the embedded bolus calculator too. Without the bolus calculator, I would often get too much insulin when correcting a high blood glucose. For instance, if in the morning my sugars would be high, I'd take some additional insulin for my breakfast bolus, to bring them down. Then I'd measure my blood glucose again in one and a half hours, and see that it's even higher. So I'd inject some more insulin. One and a half hours from that I'd measure again, and find that my sugars are still high, so I'd start to wonder whether there's something wrong with either the insulin or the cannula, but inject some more insulin to make sure. Less than an hour from that, my sugars would come crashing down, and I'd be trembling in an episode of hypoglycemia.

I did not really notice that pattern back then. But the bolus calculator taught me patience. When I'd check my glucose one and a half hours from breakfast, it would tell me "OK, your sugars are still high, but that's to be expected after the breakfast, remember? There are still many units of insulin in effect in your body, the situation is being taken care of." And an hour and a half from that, when I'd be frustrated again, it would remind me that yes, the insulin I have taken to lower the high reading is still working and already bringing the glucoses down, I don't need any extra insulin.

Here the bolus calculator reminds me that I still have 1.2 units of insulin on board to bring that 8.9 mmol/l down to target level, I only need 0.2 units more (added to the 6.9 units I need to cover the 55g of carbs in my meal) to make it perfect. Without that reminder I would most likely be frustrated that the reading is still high and dose some more correcting insulin that would then cause a hypo later on.

The bolus calculator has really helped me to avoid many lows, and to be less frustrated when waiting for the insulin to take effect. I would really like to continue using it.

In the Medtronic 640G, the pump system I'm currently trying out, there is no bolus calculator in the meter. The glucose meter does work as a remote controller, meaning you can set a bolus with it, but when you do that, neither the pump or the meter know how much insulin you took for the meal you were about to eat, and how many units of the total were dosed to correct a high. So after one and a half hours, there's no tool showing you that everything is going on just as planned, no need to panic and adding more insulin to the system does not benefit at all.

This is one of the things I'll be paying attention to when considering the switch. Will I get used to handling two devices (both the meter and the pump)? Or is it just too convenient to set the bolus with the meter? Do I really need the help of the bolus calculator anymore, or have I learned my lesson already and can think things through before stacking a dose after dose of insulin?