Wednesday, January 4, 2017

Pre-bolus: rationale and examples

 

I am always surprised at the number of patients or caregivers who are either unfamiliar with or afraid of the “pre-bolus” technique. “Pre-bolusing” means injecting insulin 25, 20, 15, 10 minutes before a meal rich in carbohydrates. While I am sure this post will be very basic for most of the readers of this blog, I feel it could be useful for occasional readers.

What is the reason behind pre-bolusing?

It is very simple. Ideally, you want your insulin injection to match as closely as it is possible the insulin secretion of a non T1D person. Unfortunately, this is not possible with insulin that is injected subcutaneously. When you are not diabetic, a meal will trigger an immediate insulin secretion in the bloodstream (in some studies, the mere thought of a meal was enough to trigger an insulin secretion).  As a T1D, the insulin you inject (or push through your pump) lands in the peripheral subcutaneous tissue and needs to be picked up. That takes a while. This is not speculation, not something “one needs to consider” – it is a fact and it has been extensively studied.

In the graph below, you can see the three essential differences between a physiological response and an injection.  (source: recovered data from https://www.ncbi.nlm.nih.gov/pubmed/26041603) Note: these activity curves are always a bit approximate in terms of absolute activity as, even in healthy volunteers, clamp studies area bit imprecise. Model curves don’t take some practical parameters into accounts. What matters is the notion of delay (due to absorption and transport) of the injected insulin peak and, later, the residual tail which is often ignored.

After an injection, even if you have matched your insulin dose and meal perfectly

  • you start by having a relative lack of insulin
  • after an hour or so and for the next two hours, you have a relative excess of insulin
  • your short acting insulin typically has a longer “tail” than a physiological response
    insulin-vs-bolus

And here is a video showing what happens when the timing of the insulin injection is adjusted

Effect of pre-bolusing on relative insulin activity.

Here are a few real life examples, all of them are high carbs breakfasts.

Injection at the start of the meal: the relative lack of insulin at the start of the digestion process leads to an excessive peak at 200 mg/dL. The relative excess of insulin after the meal has been digested slowly but surely leads to an hypo that will require a correction.

nopreinjection

 

Late bolus: in this situation, the injection came during the meal (as in “f***, I forgot my insulin”). The relative lack of insulin leads to a higher peak, that is to be expected. But the late relative excess is also more pronounced. It leads even more quickly to a potentially severe hypo that requires a couple of corrections.

delayed

Pre bolus: here, the insulin was taken some 10 minutes before the meal. The difference is drastic. The initial peak is greatly reduced and the relative excess of insulin has a minor impact. Yes, the timing possibly could have been a bit better, maybe 15 minutes. And, yes, there is still what could be considered a mild hypo. But in this case, a couple of dextrose tablets was all we needed to get back on track.

almost

20 mins prebolus:  In this case, Max woke up a bit late (holidays…) with a dawn phenomenon already significant. This gave us the opportunity for a longer wait. It ended up so well that the insulin action tail (and another small prebolus) took care of the light 2PM lunch.

prebolgood

Important note: we typically don’t prebolus if we are trending down or already below 80 mg/dL. We obviously don’t want any additional insulin activity pre-meal in those cases. Common sense, as usual, applies.

3 comments:

  1. which simulation software do you use

    ReplyDelete
  2. As a sign of gratitude for how my husband was saved from diabetes , i decided to reach out to those still suffering from this.
    My husband was diagnosed of diabetes and it was really tough and heartbreaking for me because he was my all and the symptoms were terrible, he had difficulty eating, and he always complain of stomach pain and he always Urinat often . we tried various therapies prescribed by our neurologist but none could cure him. I searched for a cure and i saw a testimony by someone who was cured and so many other with similar body problem, and he left the contact of the doctor who had the cure to diabetes . I never imagine diabetes has a cure not until i contacted him and he assured me my husband will be fine. I got the herbal medication he recommended and my husband used it and in one months he was fully okay even up till this moment he is so full of life. diabetes has a cure and it is a herbal cure contact the doctor for more info on drwilliams098765@gmail.com on how to get the medication. Thanks for reading my testimony

    ReplyDelete