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What is a square-wave bolus?

Description of a square wave bolus, how it is used and how to simulate it

Disclaimer

The human metabolism varies from person to person and some experimentation may be required to determine what time-frame works best for you. The times given in this article are only examples and should be considered as a starting point, not set in stone.

You should consult with your physician and health care team when making changes to your insulin regimen.

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What is a square-wave bolus and why would I use one?

A square-wave bolus is an insulin bolus delivered with an insulin pump over an extended period of time. The time range is usually from 1/2 hour to 3 hours.

Some pumpers utilize this tool to match the rate of food digestion with the rate of insulin activity by spreading the bolus over the length of time it takes to digest a meal. One way to accomplish this is to deliver a portion (perhaps half) of the meal bolus at the beginning of a meal and then deliver the rest in a square-wave over the next two hours or so. Other pumpers use the square-wave to reduce the spike in insulin activity. For instance, when blood glucose is a little on the low side at the beginning of a meal, one might wish to deliver the insulin over the next half hour, thus giving the food a chance to start working before the insulin activity peaks.

The square-wave bolus is useful for lengthy meals or prolonged snacking such as at a reception or banquet; for someone with gastroparesis; or whenever extending the effect of the insulin is desired. This is sometimes referred to as the pizza bolus because the fat in pizza tends to slow down glucose absorption, resulting in a delayed rise in blood glucose.

Which pumps can deliver a square-wave bolus?

The square-wave bolus is a feature of the MiniMed 507 pump and can be easily mimicked with a MiniMed 506 pump using the temporary basal rate feature. Other pumps, however, do not have a square-wave option and it would be cumbersome, at best, to try to duplicate it. To truly mimic a square-wave, the pump must have a temporary basal rate feature which allows the user to specify the length of time for the temporary rate. The Disetronic HTRON V100 and HTRONplus V100 pumps as well as the MiniMed 504 pump handle temporary basal rates in a manner which doesn't allow the user to set the duration. Trying to program a square-wave with these pumps necessitates changing the programmed basal rates to an artificial level and then (hopefully) remembering to set them back at the end of the time for the square-wave. This is potentially dangerous, as the risk for hypoglycemia is quite high if the user does not remember to, or is unable to, set the basal rate back to normal. If you wish to achieve a square-wave effect with these pumps, you could administer several small boluses manually over the desired length of time until the total bolus amount has been given.

For example: (Not recommended).

• If a bolus of six units of insulin were to be administered over a one hour time period, you could program a bolus of one unit every 10 minutes, or, a bolus of one and a half units every fifteen minutes. At the end of one hour, the total six units will have been delivered.

What happens to the basal insulin while the square-wave is in effect?

• The MiniMed 507 automatically continues to deliver the basal insulin while administering a square-wave bolus. You only need to include the insulin to cover the food in the square-wave amount.
• The MiniMed 506 does not automatically add the basal insulin, you must add the basal insulin to the amount for the square-wave. This is because the basal feature will be occupied with duplicating the square-wave and can't continue to deliver the programmed basal rate.

How to program a square-wave bolus with a MiniMed 506

Follow these steps to mimic a square-wave bolus with a MiniMed 506 pump:

1. Calculate the amount of the desired bolus and decide over what length of time you want it delivered. Add to this the amount of basal insulin which would normally be delivered during this time period. This is the total bolus amount.
2. Divide the total bolus amount by the length of time for delivery, resulting in the amount of insulin per hour.
3. Program a temporary basal rate of the amount figured in step 2 for a duration equal to the desired length of time. Note: You may need to reset the factory settings for maximum basal rates on your pump before beginning this procedure. Refer to your pump users manual for instructions.

For example: (Again, this is just an example, your rates and times may vary from this.)

Insulin required to cover food intake:	5 units
Desired length of square-wave:	2 hours
Normal basal rate:	0.4 units/hour
Total basal insulin for the time period:	0.8 units
Total bolus amount:	5.8 units
Insulin per hour for square-wave:	2.9 units/hour

Following this example, you would program a temporary basal rate of 2.9 units per hour for a duration of two hours to mimic the square-wave.

Author: Mary Jean Renstrom mjrenst@rmci.net with assistance from Bob Burnett bburnett@twcny.rr.com. Neither Mary Jean Renstrom nor Bob Burnett are medical professionals. They both have Type 1 diabetes and use an insulin pump. The information given here is based on their own personal experiences. Bob Burnett is now an employee of Disetronic USA.

Created: January 1998; Last updated: Tuesday 5 June 2001

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Reader comments

• On 18 Nov 2003 Jos Underhill wrote:

  Just to let you know that the Disetronic D-Tron Plus can deliver square-wave boluses though they call them extended boluses. They can be set to run for between 15 minutes and 4 hours in 15 minute intervals. Normal boluses cannot be given during the extended bolus and if you need to put the pump into stop for any reason the extended bolus is cancelled (an alarm warns you of this). Thanks for running the site and email lists, they have been a great help.

• On 1 Jul 2001 Dawn Wallin wrote:

  I understand what a square-wave bolus is and how to program it, however, how do you know if this is the type of bolus you need to use or if you just should increase the amount of insulin needed for higher fat meals? Are there steps to follow to figure this out? Our 9 year old son is very new to the pump and we would appreciate any help in figuring this out. Tonight he ate pizza and was 88 before dinner. 2 hours later he was 259. For most days, 1/2 unit per carb has been his supper ratio. Either it is changing, wrong, or we need to somehow use a square wave. Let us know!!! Thanks!!!

  • On 2 Jul 2001 John Neale wrote:

    Dawn - pizza is difficult food for many people. For some it seems to need a lot more insulin than you might expect, and a lot later. The reasons for this are not fully understood. You might want to talk it over with your son's diabetes team. My own strategy is to avoid pizza...