I was recently discussing with others their occasional issue of noticing “stinging” from Fiasp and Lyumjev insulins. Curious, I looked at a block of 7 of my recent days, and counted the boluses the system delivered. In that time there were 639 boluses, which is an average of 91 per day. Overall I do seem to average 90-100.
All these were “SMBs” (super micro boluses): the automatic boluses that the oref algorithm uses to bring forward some of the calculated insulin needs (rather than waiting for it all to be delivered by “basal” delivery.
Lots of small boluses
As usual for me, there were no manual boluses. I do not announce my meals or bolus for them: the system just runs in the background and applies insulin when it decides it’s needed.
So I’m not giving any big boluses, which leads to some observations:
- I’m less likely to notice boluses.
Even though I’m using Lyumjev insulin (which many people say can sting) I rarely notice any sensation of being dosed. - If I do have an occluded site, it can take a while to be detected. People using large boluses sometimes find them interrupted by alarms.
While occlusions have occasionally happened recently, they do still get noticed before too long and the site gets replaced. I just don’t feel nervous about boluses triggering alarms.
In fact the largest SMB in this period was 1.37 U. With my configuration I have occasionally seen them get up to around 2.0 U, but not this week. We’ll see what happens at Christmas feasts!
The smallest was the 0.01 U minimum supported by my pump. Here’s an example of a nice flat overnight BG trace, and as you can see the insulin is being delivered by a combination of temporary basals and micro-boluses (I have SMBs enabled all the time). So sometimes they’re tiny.
So, what was the overall distribution of sizes like across these 639 boluses?
We can see there were 45 boluses of 0.01 U. At 0.19 U there were 20 boluses. As we get larger and larger, the boluses get fewer and fewer. In fact there was only one bolus larger than 1.0 U!
If the minimum bolus size of my pump was larger (e.g. 0.1 U) then I expect there would be a higher count at 0.1 U (although some of that insulin would have been delivered by temp basal instead, with probably fewer boluses overall). I don’t have example data on that at the moment though.
Across these 7 days, my average Total Daily Dose was 36.31 U. The total of all these boluses comes to 104.82 U, which is an average of 14.97 U/day. So 41% of my insulin was being administered by bolus. But that’s not especially useful information.
Bolus/basal ratio
Historically many people have looked at the ratio between “basal” and “bolus” insulin. However today this concept is meaningless.
It was a concept of the difference between our default/background insulin needs (e.g. from long-acting insulin) compared with how much we’re bolusing for things like meals. A default guideline often mentioned by HCPs is 50:50. Obviously it would depend on the diet we ate that day: more carbs would change the balance. But that detail seems to often be ignored in discussions of this.
However today our insulin (even the “background” insulin) can delivered by a mixture of bolus and basal, and meals are also dealt with by both. So looking at the bolus/basal ratio is meaningless. If our default insulin profile is set up properly (e.g. at rates that would keep us fairly steady while fasting) then a more relevant comparison might be to compare the total of the basal rates in the profile (what we sometimes call TBB: Total Base Basal) with the TDD.
In this dataset the average TDD was 36.31 U, while the profile TBB was 23.50 U. That’s 64% of the TDD, so in a very crude analysis the other 36% was dealing with food/etc (which is less than the 41% boluses mentioned above).
I feel that’s the closest we can get to the old “bolus/basal” analysis these days. For whatever it’s worth.
Very N=1
Those 7 days were the start of the 21-day analysis from the previous article. Selected by constraints such as being a continuous block using a single profile. You can see there what the TIR/etc behaviour was over those 7 days.
Obviously there are people who use more insulin than I do, and even with SMBs-only their boluses will be larger. But I do think it’s relevant to notice that without manual boluses the usual distribution of boluses will tend to shrink in dose size.