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Splitting an Extended Bolus
Strategies for When Two Pieces of Pizza Become Four
Background Reading for this Article:Advanced Pump Feature #3: Split Bolus
A note about terminology (which varies between different pump manufacturers):
In this article…
- We use the term “Extended Bolus” to refer to what Accu-Chek calls a Multiwave Bolus, Animas calls a Combo Bolus, Medtronic calls a Dual-Wave Bolus, and t:slim and Omnipod call an Extended Bolus. In this type of bolus, some of the insulin is delivered upfront as a normal bolus, while the remaining insulin is spread out over a period of time.
- We use the term “Normal Bolus” (as this is what most pump companies call it) to refer to what Omnipod, Animas, and Medtronic call a Normal Bolus, and Accu-Chek calls a Standard Bolus, in which the entire dose is delivered immediately (upfront) with no extended portion.
- We use the term “Extended Bolus” (as this is what most pump companies call it) to refer to what Animas, Omnipod and Accu-Chek call an Extended Bolus, and Medtronic calls a Square Wave Bolus, in which some or all of the insulin dose is spread out over a specified period of time.
In the Waltzing the Dragon article “Advanced Pump Features”, we talked about the Extended Bolus.
In an Extended Bolus, a portion of the total insulin dose is delivered upfront, as a normal bolus, while the rest is delivered over a specified period of time as an extended bolus.
The Extended Bolus feature is easily accessed via the menus and buttons on your child’s pump (check your owner’s manual for specific instructions)… and all is well IF your child eats the planned amount of carbs.
But what if you expected him to eat two slices of pizza and he actually eats four? Your child’s pump may not allow you to activate a second split bolus alongside the first. To further complicate things, some of the bolus has been delivered, but there is still a remaining extended portion to be delivered that will be lost if you simply cancel the combo bolus.
What do we do now? You’re in need of an extended bolus on top of an extended bolus.
When Do We Need to Split an Extended Bolus?
Anytime your child eats more than the first serving of combo-worthy carbs (low-GI, high-protein, or high-fat foods).
How Do We Add an Extended Bolus to an Existing Extended Bolus?
Since your insulin pump may not allow you to directly layer an Extended Bolus on top of an existing Extended Bolus, we need to think outside the box. There are two methods that our families have used for dealing with this situation:
Method 1: Delay Activating the Extended Portion of the Bolus Until the End of the Meal
If you are not sure how much pizza, pasta, or rice and beans your child with diabetes will eat, you can:
- Start with the smallest serving that you are confident your child will eat (while still anticipating that she will likely eat a second serving or more).
For example, if you’re pretty sure she will eat one slice of pizza, but think she may eat two or three, start with a one-slice serving.
2. Next, manually or through the pump’s bolus calculator, figure out what both the normal and extended portions of the insulin dose would be for that first, small serving, by using the Extended Bolus function (see above for manufacturer-specific feature names) within the Bolus Calculator.
Let’s say that the pump bolus calculator recommends 3.0U total insulin to cover the carbs in that one slice of pizza. If you enter a 60/40 split, that would mean 1.8U as the normal (upfront) portion of the bolus, and 1.2U as the extended portion of the bolus.
3. Go ahead and deliver ONLY the Normal portion of what will be a split bolus. You may prefer to back out of the split bolus function to do so, and simply use the Carb Calculator function, or even the Normal Bolus function.
For example, using the same 60/40 split as above, you would deliver 1.8U of insulin , as a normal bolus, for that first slice of pizza.
4. Make note of the as-yet-undelivered Extended portion.
In this example, the remaining insulin to be delivered as an extended bolus is 1.2U.
5. If your child decides that she’s done after that one slice, you can go ahead and deliver the Extended Bolus for that slice (as described in step 8), OR
6. If she wants more pizza, repeat steps 2 – 4 for each additional serving.
If your child has a second and then a third slice of pizza, you would, for example (assuming for simplicity that the slices are all identical in carb content), deliver 1.8U (upfront) for the second slice, and then 1.8U (again, upfront) for the third. Each of these amounts would represent 60% of the total carbs needed to cover each slice, and would leave 1.2U and 1.2U still to be delivered.
7. Once your child has finished the meal, add up the amounts of the Extended portions still to be delivered.
For example, 1.2 + 1.2 + 1.2 = 3.6U
8. Deliver that amount as an Extended (or Square Wave) Bolus, with zero units up front, and with the total extended over your chosen time period.
For the example of 3 slices of pizza, 3.6U would be delivered as a (0:100) 100% Extended Bolus over the next chosen number of hours.
For the example of 1 slice of pizza (if you skipped here from step 5), 1.2U would be delivered as a (0:100) 100% Extended Bolus over the next chosen number of hours.
This method works great if you anticipated the extra servings. But what if you thought, “there’s no way she’ll eat more than 1 slice” and already activated the extended portion of the combo bolus, some of it was delivered and THEN she asked for a second serving? Now you need Method 2…
Method 2: Cancel the Existing Extended Bolus
If your child’s request for extra servings of a combo-worthy food took you by surprise, you can:
- Cancel the remaining extended portion of the bolus, making sure to first note the amount of this extended portion that has yet to be delivered. These figures can be obtained on the Extended Bolus Cancel screen while cancelling, through the pump status screens before cancelling, or through the pump history after cancelling.
For example, the history may show that 0.3U were delivered out of 1.2U, leaving 0.9U still to be delivered in the extended portion of the bolus.
2. Deliver the normal bolus portion of insulin for the second serving (and third, or fourth, as needed) as outlined in steps 2-4 in Method 1 above, making note of the additional extended boluses that still need to be delivered.
Using the same second and third example slices from the Method 1 example above, you would deliver 1.8U and then 1.8U (both upfront), leaving 1.2U and 1.2U still to be delivered.
3. Once your child has finished the meal, add up the amounts of the Extended portions still to be delivered.
For example, 0.9 + 1.2 + 1.2 = 3.3U
4. Deliver that amount as an Extended (Square Wave) Bolus, with zero units up front, and the total extended over your chosen time period.
For example, 3.3U would be delivered as a 0:100 Extended Bolus over the next chosen number of hours.
The above information was reviewed for content accuracy by clinical staff of the Alberta Children’s Hospital Diabetes Clinic.
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