Variable insulin effectiveness and nonlinearities

the other day our son had a high carb breakfast (60 grams) and he when we tested him a 2.5 hours later he was on the edge of going low with a large amount (for him) of active insulin. This got me thinking about insulin effectiveness and how it works. His carb ratio changes pretty dramatically over that time period, from about 11 at 9:30 when he ate, to 17 or so by 11:30 or 12. My question is was the tail of the bolus that we gave at 9:30 but was acting at 11:30 acting with the reduced effectiveness of the earlier morning or the increased effectiveness of the 11:30 timeframe? If the latter, which I assume is the case, it implies that the whole notion of a carb ratio doesn't really work, and that in particular large boluses have a nonlinearity to them since more of the bolus will be working later in the day (when presumably the insulin is more effective). Are people accounting for this?

thanks

Bruce

Hi, Bruce.  I understand what you are saying, although I don't really have an answer.  During the honeymoon period, my daughter would ALWAYS drop after a meal of spaghetti, even when I would back off on her bolus.  Now, a year later, this doesn't happen.  I think it is just that all carbs are not equal and absorbed at different rates at different times of the day.  And, perhaps, some days your son is more sensitive to the insulin than others.  While on injections, my daughter's breakfast carb/insulin ratio was 10 grams/unit.  By supper, she was 15 grams/unit.  She just started on the pump this week, so it is a whole new learning curve for us.  On the pump, she is set for 18 grams/unit.

Carb ratios are very effective, I used them for about 20 years (10 on shots and 10 with a pump) and it works well most of the time.  A couple things that may help you:

- Adjusting insulin is an art, as much as a science.  Over time, you'll learn how specific foods or times of day affect your son and dose accordingly.

- Like Shandra mentioned, many people have dawn phenomenon and blood sugar is higher in the morning.  In your example your son at a higher carb breakfast late in the morning.  In that situation your son might take slightly less insulin than normal and test in an hour, then give the remainder.  

- Do the same for high carb or high fat meals.  Use a dual wave bolus or take a smaller amount of insulin, then test in an hour and give the rest based on my current blood sugar.  It helps the insulin hit at the right time.

- There's something called the "Chinese Restaurant Effect" where high carb meals take more insulin than the actual carb count.  A big meal or high fat meal takes longer to digest too, so it can take a while to hit the blood stream.

- Make sure your son's pump basal rate is correct.  Carb ratios can't be reliable if base insulin isn't correct.

- Make sure your son's insulin duration time is accurate too.  

Hope this helps.