After getting basal rates that I believe, I’m up to the part of my on-going “Let’s finally figure out the right pump settings!” project where I check my bolus amounts. I have long suspected that I am over-insulinized in the morning, since I frequently need a snack between 10AM and noon to prevent a hypo. Now that I know my basal rates are correct—I can plank pretty well if I don’t eat—the fiery finger of blame points at my bolus ratios.
Last week, after my awesome endocrinologist “ooh-ed and ahh-ed” over my much improved A1c, I asked her my burning question about active insulin (a.k.a., insulin on board or IOB). “When I’m bolus stacking, when do I consider active insulin and when don’t I?” I frequently eat multiple times during any given five hour period, which means that I have multiple doses of insulin working on their respective meals. I’ve noticed that sometimes I have to take that insulin into account, since its “long tail” will continue to lower my blood glucose for a bit longer. Other times, if I subtract out that IOB, I see high blood sugars later because that insulin was still needed for the previous meal/snack. What to do?
Her advice to me (and this supposes that my pump’s “active insulin” setting is correct) was to subtract out the active insulin if the bolus was three or more hours ago, since digestion should have finished by that point. This is when I’m already near my BG target and have IOB.
(Since I’m often back into the lower part of the “happy” range 2-3 hours after a bolus and/or I didn’t see much of a rise at all, this is probably another indicator that I’ve been taking in too much insulin. That and the fact that bolusing frequently comprised more than 70% of my total daily dose, which is higher than the 40-60% that most recommend. As a result I was eating a lot of “defensive” carbs to prevent lows, which seems to be leading to highs later in the day.)
I had been trying less aggressive bolus ratios over the weekend with some success, but acting on hunches and suspicions is bad form, so today I decided to be a bit more rigorous. Armed with my endo’s advice, a measuring cup, notebook, and pen, I set out to figure out what my bolus ratios need to be. Here is the data through lunch:
05:03 - 164 - - Wake up... yawn. 05:45 - - - Swim 1000 yards in 20 minutes. Disconnected for 35 minutes. 06:21 - 121 - 2.9 u - Granola bar (24g) = 2.6u + 0.3u correction (using 1:9 ratio) 07:34 - 149 - 6.5 u - Cereal, milk, eggs, sausage (64g) = 7.1u (but I know this is too much) 10:18 - 104 - - There was a bit of walking around in the previous hour 11:15 - 104 - 1.0 u - 1/2 donut from the box next to the printer (19g) = 2.3u - 1.3u IOB 12:00 - 120 - 8.3 u - Sandwich (35g), Yogurt (18g), Apple (~20g) = 75g = 8.3 (using a 1:9)
This morning looks pretty successful. Let’s try to reverse engineer a possibly correct bolus ratio. I ate 24+64=88 grams of carbohydrates for breakfast, and delivered 9.4 units of insulin. That yields, let’s see here, 1 unit for 9.4 grams, or about 1:9. But we know that’s too much from past experience (including this morning).
The 9.4 units of total insulin includes whatever insulin was needed to make up for the 35 minutes that I was disconnected from my pump while swimming and a correction of 0.3 units, which may or may not be the same. Let’s run the numbers again a few different ways.
Not taking correction into account: (24 + 64 g) / (2.9 + 6.5 units) = 9.4 g/unit
Just using the correction: (24 + 64 g) / (2.9 + 6.5 – 0.3 units) = 9.7 g/unit
Using the time off pump: (24 + 64 g) / (2.9 + 6.5 – 0.9*(35/60) units) = 9.9 g/unit — 0.9 units/hour is my basal rate at that time in the morning.
What’s the lesson here? What ratio should I use? 9.4? 9.7? 9.9? Since my pump only works in whole units for the ratio, it’s a choice between 1:9, 1:10, or carrying a calculator/MATLAB everywhere with me. (The pump version one generation after mine does allow fractional ratios.) The 1:9 ratio is clearly too aggressive given what’s been happening to me, so I’m going for 1:10, which has a certain easiness to it, too.
Let’s see what tomorrow brings.