Bolus this, basal that... insulin pumping has a language all its own! So just like everything else in the world of diabetes, it never hurts to learn more, whether you're a longtime PWD (person with diabetes), someone newly diagnosed, or just now starting out on an insulin pump, or just curious about how they work. Luckily, our weekly advice column Ask D'Mine has answers from veteran type 1, diabetes author and educator Wil Dubois.

In this first of a two-week focus on insulin pumps, Wil offers a pump primer before digging into some nitty-gritty dosing details...

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Cindy, type 1 from Colorado, writes: I use a Medtronic pump and I want to know what happens to the correction part of a complex bolus. For instance, if I were to take a square wave bolus for a meal, but I'm also correcting an over-target pre-meal blood sugar, does the correction also get "squared," or is it delivered 100% before the meal portion?

Wil@Ask D'Mine answers: Wow! What a great question! But before I dig into the answer for you, let me get the rest of the readers up to speed on funky pump boli. Insulin pumps, as you'll recall, are the ultimate VCRs—they have a ton of functions most people don't understand and never use. But even if your VCR flashed "12:00" all day every day, like my Mom's did for years, it would still work just fine to play movies. (Can you actually even still buy a VCR — or have DVDs killed them all off?) Anyway, while not setting the clock on an insulin pump would probably keep it from working, there are a whole host of pump features that aren't strictly needed when using a pump—and a square wave is a prime example of that.

Let's quickly review how the pump works: First, the pump does away with the need for basal shots such as Lantus, Levemir, or NPH by providing a constant drip of fast-acting insulin called a basal rate. Some people have one rate that runs all day long. Most have at least several different rates. Others have a dozen or more. It just depends on how much of a control freak you are, and how 'effed-up your body is. Some friends in the diabetes online community have shared that you can actually live, although not in a very healthy way, on basal drip alone.

But of course where pumps really begin to shine is at meals. If you estimate (to the best of your ability) the carb count of a meal and give this info to the pump, it  will crunch the math of the insulin to carb ratio for you and deliver the necessary insulin for the meal in a very precise fashion. But wait, there's more! If the pump knows your blood sugar, and you aren't in target, the pump can fix that, too, at the same time. The good ones can even work in reverse and lower the volume of meal insulin if you are below target before eating.Bolusing-Tshirt

But it gets better still.

Not all meals are created equal. Some are very high in fat. Others are crazy mixes of fast- and slow-acting carbs. Thus the complex boli. They go under different names, but there are essentially two types. In one type, the total meal bolus is extended over a period of time that you choose. Medtronic calls this a "square wave" bolus. These are great for all-you-can-eat Chinese buffets, Super Bowl parties, the Never Ending Pasta Bowl at the Olive Garden, and other high-fat meals. The other type of complex bolus is a compound delivery with a percentage delivered at once and then the remaining balance over time. Medtronic calls this a "dual wave" bolus, and it rocks for meals like pizza where the crust and the sauce hit the blood sugar faster than the meats and cheeses do.

End of pump lecture.

Now, when I got your question I immediately knew that any well-designed pump should deliver the correction first, as that's a here-and-now problem, and then it should do whatever you told it to with the rest of the insulin. But, of course, the reality doesn't always live up to the promise, so I set out to discover how the Med-T pump handles your situation.

First, I tried to figure it out myself by looking at CareLink Pro insulin delivery reports, and screwing around with our clinic's demo pump, but I wasn't 100% sure what was going on, so next I fired off a distilled version of your question to all my Med-T contacts and they universally responded with: We'll get right back to you on that.

Clearly, no one knew the answer.

In the week since, I've been getting some varied feedback. But it seems the answer is that with a "dual wave" bolus, the correction is added to the up-front portion of the bolus and the square wave is a little mor complicated. According to both my Med-T contacts and the online users' guide, if you enter a BG either with a linked meter or manually, the option for a square wave bolus will be locked out. So the correction is neither delivered up front nor squared. Square corrections are prohibited, apparently. No corrected squares allowed.


Well, I guess, in some perverted engineering way, it kind of makes sense, as you really don't want to square your correction—and if you are getting the correction up front it's now a dual wave not a square wave... but this just seems stupid to me. But as I noted, intelligent design is not part of pump evolution.

A work-around, of course, would be to take the correction first, then enter the square wave for your all-you-can-eat Chinese buffet, Super Bowl party, Never Ending Pasta Bowl, or other high-fat meal.

Still, how annoying, as the whole point of a pump is to make life easier.


This is not a medical advice column. We are PWDs freely and openly sharing the wisdom of our collected experiences — our been-there-done-that knowledge from the trenches. But we are not MDs, RNs, NPs, PAs, CDEs, or partridges in pear trees. Bottom line: we are only a small part of your total prescription. You still need the professional advice, treatment, and care of a licensed medical professional.

Disclaimer: Content created by the Diabetes Mine team. For more details click here.


This content is created for Diabetes Mine, a consumer health blog focused on the diabetes community. The content is not medically reviewed and doesn't adhere to Healthline's editorial guidelines. For more information about Healthline's partnership with Diabetes Mine, please click here.