Extended Bolus vs Increased Basal

I’m wondering what the primary difference is between an extended bolus and an increased temp, or otherwise, basal. I have a difficult time in the evening preventing a spike 3+ hours after I eat. I resolved this by tripling my basal at the start of my meal and keep it at that rate for 3 hours. This has worked pretty well. This is not a temp basal but rather pay off my daily basal profile. However, yesterday I tried fasting for the first time. My BGs were incredibly stable for the whole day with only a 5% sd which I’ve never before experienced. Unfortunately, I forgot about my tripling of my basal in the evening and as a result had a hypo. That got me wondering whether it might not be safer to try the extended bolus instead of the fixed increase in basal. Does anyone used the extended bolus for these types of situations? TIA!

Let’s suppose that the normal basal rate is 0.5 U/h, and that you increased that to 1.5 U/h for 3 hours. This amounts to (1-5-0,5)*3 = 3 U of extra insulin delivered over 3 hours. If you instead dialed in 3 U in the form of an extended (square-wave) bolus over 3 hours, the effect would be identical. An important difference, however, is that pumps do not take any increased or decreased basal (temp or normal) into account when they calculate IOB (“active insulin”). So, if you used a pump’s bolus wizard during or after those 3 hours, the IOB would be incorrect. which could result in an erroneous bolus.

IMO, it is not a good idea to schedule increased basal to address meals, because of the IOB calculation and, even more importantly, for the reason you mentioned: it is too easy to forget about it and end up low. In the situation you described, I’d recommend using an extended bolus: just calculate however many extra units you scheduled in the form of increased basal, and deliver these units as an extended bolus over 3 hours.

Incidentally, DIY closed-systems use temp basals all the time, but their algorithms take them into account correctly when they calculate IOB.


Thank you. This is exactly what I want to do. I didn’t realize that about basal not being in the IOB. I’m so glad you pointed that out. Yes, that is exactly what happened to me. I forgot that I had programmed a triple increase, but then didn’t eat anything, and hence the low. The extended bolus definitely seems the way to go.

I am so waiting for a closed loop for the OmniPod but I think it is a long way in coming. I would try out the DIY closed-loop system but I really like the OmniPod. I’ve never used any other pump though.

I teach using temp basal reductions (in percentages) for treating lows and use an extended bolus to treat a high just because the math is easier. Many people have multiple basal rates through-out the day and it is hard to remember the numbers or calculate 150% of 0.8 units an hour. Many people are good at knowing that they need a 2-3 unit correction for a high and using an extended form makes this a gentler correction and provides to option of shutting it off it all the correction isn’t required. The dual-wave, or setting an extended bolus with 7% up front gives a fast start to the correction with a taper at the end that can prevent lows. The IOB calculation is useful to know as well.

Thank you. Yes, I agree, for me it is easier to use the absolute value rather than percentage for treating a high. I am going to experiment with the extended bolus for my evening time after I start eating again. I’m still fasting, but I don’t know if I’ll be able to fast for the full 5 days. Today is my 3rd day, but with some food taken for lows.