Diabetes Math

Here’s a little math problem for you. Your 13-year-old T1 has been sick with a nasty cold for a couple of days. At 2 AM you wake up to Dexcom alarm and see that your T1’s BG is 275 and trending up. You get up to give her a correction bolus. The pump says you should give 4 units of insulin for correction to bring BG to target of 100. You also notice that there are 17 units of insulin left in the pod. Your T1’s basal rate of insulin is 2 units per hour and you will not be able to change the pod until about 7:30 AM. You have ruled out a site failure, determining that it is working more or less OK. You are able to administer insulin correction via the pump and/or via a shot. How much insulin do you give her? How do you deliver it? For a bonus question, how long will it take you to fall back asleep after you are done?

If you quickly run the numbers in your head, it looks relatively simple. 17 units of insulin in the pod minus 11 units needed to last until 7:30 AM minus 4 units recommended for correction = 2 units left to spare. Administer a 4 unit correction via a pump. Fall back asleep within next 15 minutes.

Nice try. You get an F in diabetes math. If you administer a quick 4-unit correction, you could probably get back to sleep in 15 minutes. However, you will be woken up again very soon because the BG will continue to climb up, the alarms will continue to blare, and you will have to do this all over again. Diabetes math is far more complicated than what it seems.

The remarkable thing about our little math problem is that every bit of information I provided is relevant and changes the equation. So let’s do it together.

Age and sickness are important. Teenage hormones are not kind to T1D and can lead to heightened insulin needs, sometimes unpredictably. Illness also causes BG to go up. Both factors, combined with the fact that due to illness V was sedentary for a couple of days, lead to increased insulin resistance. The pump is not programmed to change its calculations based on these constantly moving targets. It recommends the amount of insulin needed based on preset ratios and estimated active insulin remaining (AKA IOB or Insulin Onboard). So when you see a BG of 275 and trending up, under these circumstances you should think about how much more insulin it’s likely going to take to bring V into a better range. This knowledge only comes with experience and trial and error.

I know from experience that in this scenario 4 units are completely insufficient. I also know from experience that when V’s BG is over 250, insulin resistance kicks in like there’s no tomorrow. And let’s not forget that her illness, hormones and lack of activity are also contributing to insulin resistance. This is time to dose aggressively. Not only will you need to give a much bigger correction, you should also increase basal insulin for a couple of hours. How much? Once again, informed by trial and error data, we need to jack it up to 200%. If you do the math again, you will quickly realize that 17 units left in pump are not enough.

Here is the answer. Give a correction of 7 units via a shot. Not only does it save you insulin in the pod, it delivers it more quickly and bypasses any potential absorption issues with pump site. The extra 3 units over the recommended 4 will account for insulin resistance and for the fact that by the time insulin starts working V’s BG will already be around 300. Then, increase temp basal rate by 100% (to 200% total) for 2.5 hours.  Three hours would be ideal, but there is not enough insulin left in the pod. 4 units for 2.5 hrs, plus 2 units per remaining 3 hrs equals 16 units. V will make it to 7:30 AM with only 1 unit to spare.

Mind you that you do this math in your head at 2 AM because you can do this shit like a boss. Then you go downstairs to get insulin vial and syringe. You go back up and turn on the lights. You are fully awake now, and you better be fully awake because you have to draw the inulin and do the shot. You go back to bed hoping that your math is not off by too much. Experience tells you that in this particular scenario you may not have given enough insulin (believe me!). Forget target BG of 100. Due to illness you haven’t seen it for a few days. Your goal is that 1. BG will start trending down instead of up and 2. at 7 AM V will wake up with BG closer to 200 than 300. But it’s 2 fucking AM and you need to go back to sleep. Which, to answer the bonus question, takes you at least one hour.

When you wake up in the morning, while you may be feeling tired, foggy and grumpy, you are rewarded with an A in diabetes math.

BG peaked at 300 around 3 AM and went down to 182 by 6:45 PM. GOALS MET!

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