Extended Bolus: How, When & Why

Pizza Night and Beyond: extended bolus can reduce bg spikes (and your stress!)

Michelle MacPhee
D-Mom, Creator/Co-Founder of Waltzing the Dragon

Frustrated by blood sugar spikes after pizza, pasta, burgers and ice cream? We'll share some practical tips on how and when to use an Extended Bolus (also known as a Combo Bolus or Dual-Wave Bolus), as well as some practical strategies for taming those blood sugar spikes.

But first the theory behind this handy insulin pump feature...

pizza slices on white background

Insulin pumps allow you to alter how much of a bolus is delivered and when, resulting in different bolus shapes:

Normal Bolus

delivers the entire dose immediately. For example, if 6 units (U) of insulin is the desired dose, all 6U will be delivered within moments of pressing the "Okay" button. This is most similar to giving insulin by injection; the insulin acts as quickly as possible for its type, because the entire dose is being delivered at once, and so will return high blood sugar to target more quickly than the other bolus shapes (below).

When should I use a Normal Bolus?

For most people, a Normal Bolus will be used most often. It may be helpful for carb-containing snacks/meals with low amounts of protein and fat. As a correction for high blood glucose, it's the only logical choice, since you want your blood sugar to return to target as quickly as possible.

Extended Bolus (a.k.a. Square Wave Bolus)

spreads the dose out over a specified period of time with 0.0 U given up front; there is no initial "dump" of insulin which may lead to a low if the insulin gets in before the food is digested. For example, if 6U is the desired dose, you could choose to extend the bolus delivery over 3 hours, meaning that equal fractions of the total dose will be delivered every few minutes so that the 6U of insulin will be delivered over the 3-hour period.

When should I use an Extended/Square Wave Bolus?

An Extended Bolus may be helpful for snacks/meals that contain low amounts of carbohydrate, with moderate to high amounts of protein and/or fat, such as steak and a salad alone. It can also be helpful when your child comes into mealtime with a blood glucose reading that is on the lower side, and you want to ease into the insulin action to allow blood sugar to rise before insulin affects it. It also may be appropriate for individuals who have a medical condition that causes slow or delayed digestion (such as gastroparesis).

Tips from the Trenches

If Paul has a blood glucose that is on the lower side (and he doesn’t want to eat extra, high-GI carbs to bring his blood glucose up), if we give an extended bolus over 0.5hrs for a moderate GI meal, most times his blood sugar will balance out nicely without going low first. ~Danielle

Combination: Normal + Extended Bolus (a.k.a. Combo Bolus, Dual Wave Bolus, or Multi-wave Bolus)

(Omnipod, Tandem t:slim and Ypsomed use the same "Extended Bolus" term as above)

is a hybrid of the first two insulin delivery modes: some specified portion of the total insulin bolus is delivered upfront, as a normal/straight bolus, while the rest is delivered over a specified period of time as an extended/square wave bolus. For example, given a 6U dose delivered as a 60/40 combination/square wave bolus over 3 hours: 60% of the total dose (or 3.6U) will be delivered within seconds of pressing the "Okay" button; the remaining 40% (or 2.4U) will be delivered (in equal fractions) every few minutes over the next 3-hour time period. The result is an initial dose to deal with faster-digesting foods, plus an extended tail of insulin action to deal with the slower-digesting foods.

When should I use a Combination Bolus?

For snacks/meals that are predominantly low on the glycemic index (such as plain pasta, spaghetti with tomato sauce, barley, or pulses like chick peas or black beans) OR for foods that contain a mix of a moderate to high amount of carbs plus moderate to high amounts of protein and/or fat (such as pizza, pasta with a heavy cream or cheese sauce including home-made macaroni and cheese, a burger with fries, cheesy / meaty / deep-fried Mexican food, popcorn with butter). A combination bolus may also be helpful for "grazing", when the person with diabetes may be eating small amounts of food over a few hours (for example, movie night at a friend's house; a cocktail party; a kids' birthday party with a free-access snack table).

More info on how different foods digest at different rates:

Why Use an Extended Bolus?

The benefit of having options in terms of the shape of the bolus is that the rate of insulin delivery can be better matched to how quickly or slowly certain foods are digested: quick delivery can be used to deal with quickly-digested foods, mediating the blood glucose spike that may strike after eating starch and carbs; a prolonged delivery can be used for slower digesting foods, avoiding the lows that often set in when insulin acts more quickly than the slowly digested foods do. As a result, we can even out the blood sugar peaks and valleys that may follow certain meals, leading to more successful blood glucose management... better feeling, lower A1C's, better health!

How Do I Know If I Should Extend the Bolus?

Keeping in mind the above examples (and those in the Glycemic Index Explained and Choosing the Right GI for the Job pages), check your child's blood sugar before eating and 1 hour after eating a meal like pasta / spaghetti, pizza, burgers, fries, steak and baked potato, rich cheesecake, full-fat ice cream, chickpeas, buttery popcorn...). If your child's blood glucose has dropped as of the 1-hour point, this may be an indication that the meal she has just eaten is appropriate for an extended bolus. Now have her check her blood glucose a few hours later... if the reading has sky-rocketed, this makes the need for an extended/dual-wave bolus even more likely.

A Real-life Example:

Before my son had an insulin pump, and before I learned anything about the glycemic index, these were his blood sugar readings (in mmol/L) one evening after fast-food chicken nuggets and fries (a high carb, high-fat meal):

5:00 PM (before eating): 8.2
6:30 PM (1-hour after he finished eating): 5.1
9:00 PM: 13.2
1:00 AM: 18.7 (despite the usual correction 4 hours earlier)
7:00 AM: 15.6 (despite previous corrections at 9 PM and 1 AM)

This Is What Happens:

There is too much insulin early into the slowly-digesting meal, so blood glucose drops. Then there is not enough insulin available later, when the majority of the food digests and enters the blood stream as glucose - that is, the insulin "tail" is too short, leaving much of the glucose in the bloodstream long after the meal, so an extra bolus of insulin is needed* to get this excess glucose out of the blood and into the cells. However, if the insulin is delivered as an Extended or Combination Bolus, then less insulin is given up front, and the insulin tail is extended, better matching the slower rate of digestion of the food. (*Plus the fat leads to insulin resistance, a pesky problem for adults and children with diabetes... but that's another story!)

Notes About the Extended Bolus:

  • This typical blood glucose pattern (a drop followed by highs) indicates use of an extended bolus if, and only if, the basal rates have previously been confirmed. Otherwise, it's possible that the early drop in blood glucose was due to excess basal insulin, while the steady climb post-meal could coincide with insufficient basal insulin.
  • An accurate carb count and correct insulin:carb (I:C) ratio should also be confirmed. If too much insulin was given for the meal (either because the carbs were over-estimated, or the I:C ratio is too strong) then it's possible that the early low blood sugar was simply due to excess insulin; the persistent highs that followed could then be due to the Symogi effect, or a "low rebound".
  • To help sort all this out, gather the clues together to look at the whole picture: Are the basal rates, I:C ratios, carb content confirmed? Was the meal low glycemic index, high protein*, and/or high fat? Was there an initial drop in blood glucose followed by later high blood glucose? If so, you could try an extended bolus, note the results, and make adjustments from there.
  • A Continuous Glucose Monitor (CGM) is a particularly useful way of visualizing the effect of problem foods on blood glucose - and can be a very efficient way of perceiving the need for an extended bolus.
  • If you plan to use an extended bolus at a given meal, and your child's blood glucose is above-target before that meal, remember to separate the blood glucose correction from the food bolus, delivering all of the correction dose up front (and well in advance of the meal, whenever possible). You then program an extended or combination bolus only for the food bolus. If you don't split the two, a portion of the correction dose will also be extended over a period of time, delaying the return back to in-range glucose readings.

Then you may need to experiment with giving a different percentage of the total bolus upfront, or with the duration of the extended portion of the bolus.

See Tweaking an Extended Bolus

Tips from the Trenches

When this happens in our family, instead of giving a normal bolus for the high GI food we are using to balance the mistake, we use a 100% extend over the amount of hours we would have done the combo for. This usually works out nicely. (Except that when we’ve had to use this, Paul is usually full beyond belief and now has to cram more food into him!) ~Danielle

The above information was reviewed for content accuracy by clinical staff of the Alberta Children’s Hospital Diabetes Clinic.