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?


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  2. I'm considering EXACTLY the same thing. I have used the Combo for the last 4 years and I'm looking at replacing it with the 640G.
    What were your conclusions? Did you change pumps? How did you get on and have you any thoughts to pass on?