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Adjusting Insulin in a Pump Program: how insulin action impacts blood glucose

If your child has predictable lows (or high BG), you may need to adjust their insulin doses. But which dose, and how much should you adjust by? You can start the process here by looking at how and when the action of rapid-acting insulin affects BG in a pump therapy program.

Before Reading This Article...

Before making any changes to insulin doses, it is important to understand the action of insulin (the onset, peak and duration of different types of insulin). Therefore, as background for the information that follows, we recommend you first review Insulin Types & Action.

You may remember that:

    1. Conventional Program in which you give 3 injections of N/NPH and/or rapid-acting insulin
    2. Basal-Bolus Program with Multiple Daily Injections (MDI) in which you give 4 - 6 (or more) injections of long-acting plus rapid-acting insulin
    3. Pump Therapy program in which you infuse (rather than inject) rapid-acting insulin only.

On this page we are talking about an Insulin Pump Program (#3).

  • Your child's current blood glucose (BG) is a result of several factors, including the way that a particular insulin behaves, which we call "insulin action." In other words, insulin action describes how quickly the insulin starts to affect blood sugar, when it peaks (has the most power), and how long the effect of the insulin lasts.
  • Rapid-acting insulin starts to work in 15 minutes, peaks at 1 hour, and lasts 3-5 hours.

For the discussion that follows, “rapid-acting” insulin refers to Humalog®, NovoRapid®, or Apidra.® (Note that Fiasp® has a different insulin curve.)

How Insulin Affects Blood Sugar in a Pump Program

This insulin action diagram for a pump program shows that the blood glucose at a given time is affected by a certain previous insulin dose.  If we follow the curve back from breakfast, for example, we can see that it leads to bedtime, when a dose of N/NPH was given. If we follow the rapid-acting curve back from lunch, we can see that it leads to breakfast. 

Basal and Bolus infusion in an Insulin Pump Therapy program
Basal and Bolus infusion in an Insulin Pump Therapy program

Another way of expressing this relationship is to say that:

  • Blood Glucose before breakfast tells you about how well the overnight basal rates are working.

  • Blood Glucose before lunch tells you about how well the morning basal rates + breakfast bolus of rapid-acting are working.

  • Blood Glucose before supper tells you about how well the afternoon basal rates + lunch bolus of rapid-acting are working.

  • Blood Glucose at bedtime tells you about how well the evening basal rates + supper bolus of rapid-acting are working.

For example, if the breakfast blood glucose is consistently out-of-range (high or low), you may want to change the overnight basal rates; if the supper blood glucose is consistently out-of-range (high or low) you may want to change the dose of lunch rapid-acting insulin and/or the afternoon basal rates.

The above information was adapted with permission from The Alberta Children’s Hospital Diabetes Clinic information handouts.

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