For a person wearing an insulin pump to help manage their Type 1 diabetes there is a lot of behind the scenes action going on all the time, 24 hours a day. At any given moment, someone wearing an insulin pump can be getting insulin from their pump from either a basal rate, a correction bolus or a carb bolus (hence the 3 Bs…basal, bolus, bolus).
At a minimum the person wearing the insulin pump will be getting a continuous flow of insulin through their pump to keep their blood glucose as steady as possible, this is called the basal rate. Most pumps allow for different basal rates throughout the day to try to mimic the way a working pancreas would put out insulin. Most people find they need different rates for different times of the day. My six year old son, for instance, needs the most basal insulin from 9:00pm to 11:00pm. It may be growth hormones, or sleep that requires this amount of insulin, but whatever the reason, a working pancreas would know what to do, so the person programming the pump (mom in this case) must do the same. Throughout an entire day my son has 8 different basal rates all determined by me by checking his blood glucose a minimum of 10 times a day then logging all the numbers and deciding where he needs more or less insulin. I am his working pancreas.
Basal rates are part of a unit. Some smaller people like my son have basal rates such as .150, .325, or .900. That means that over the course of an hour, my son gets .150 units of insulin doled out to him in equal amounts to keep his little body as steady as possible. In a perfect world the basal rate should be set so that the person with Type 1 diabetes does not experience a high or a low blood sugar, just like a person with a working pancreas. Nothing is perfect in the world of Type 1 diabetes, but that is a whole separate post. So lets just leave it as ‘in a perfect world’ the basal rate should keep a person with Type 1 diabetes in a normal blood glucose range of 80-120.
Now to explain the carb bolus, the 2nd B. In an insulin pump there is an insulin to carb ratio. In fact, in my son’s pump there are 6 insulin to carb ratios. Insulin to carb ratio (I:C) is the amount of insulin that is needed to cover a certain amount of carbs being consumed. So for breakfast my son’s I:C is 1:12. So for every 12 carbs he eats (strawberries, toast, cereal, or whatever) I push buttons on the pump to give 1 unit of insulin. So if my son were to eat 48 carbs at breakfast he would get….waiting for you to do the math….if you answered 4 units of insulin than you would be correct. If my son ate 48 carbs at breakfast he would get 4 units of insulin. These are determined the same way. There is a parameter we follow. Two hours after eating the person with Type 1’s blood glucose should be no more than 50 points higher than when they started the meal. If the person’s sugar is not there, say too high or too than you know to move the I:C ratio to allow for more or less insulin. You achieve the ratios by testing glucose, logging, making changes and testing glucose again at the same time the following day.
Lastly correction bolus, the 3rd B. Insulin Sensitivity Factor (ISF) is the amount of insulin that is needed to lower the blood glucose when it is too high. My son has 3 ISF settings in his pump: 1:100, 1:150, and 1:110. That means, quite simply, that my son receives a certain amount of insulin to get his number in range according the settings that I have placed in the pump. In the morning, my son’s ISF is 1:100. His target blood glucose is 100. If he wakes up with a blood glucose number of 200 he needs to go down 100 points to get to his target of 100. When I put 200 into the pump, the settings that I have created would tell me that he needs 1 unit of insulin to drop him the 100 points. If my son’s blood glucose number was 300 upon waking he would get….waiting for you to do the math…if you answered 2 units of insulin you would be correct. Trick question. If my son woke up to a number of 225, how much insulin would he get to come back into range?
So back to my original statement that at any given time there is at least one insulin pump setting working on my son’s blood glucose up to a maximum of 3 different settings. Scenario time: If my son were to wake up with a blood glucose of 200, and he ate 48 carbs, he would receive a bolus for both numbers. 1 unit for blood glucose number and 4 units for his food totaling 5 units. 5 units plus the basal rate for that time of day begins coursing through my son’s blood. Now 2 hours after eating his feels shaky and test his sugar, he tests at 48!!!. Somewhere somehow he got too much insulin, whereas the day before all these settings worked perfectly. So my mind starts to question: Could his I:C need changing? Or maybe it’s the ISF for that time of day that needs changing? Or maybe the basal rate is too high close to the 2 hour point?
Right off the bat there are 3 things that need to be looked at and I only get 1 shot to fix it, the next day at the exact same time. That is not mentioning that exercise, illness, stress, weather and whatever else can affect blood glucose readings, so it may not even be basal, I:C, or ISF that need tweaking. It may just be Type 1 diabetes playing that sick joke on us again.
With all these components affecting 1 blood glucose number it’s wonder when we have any numbers in range. Must be the correct alignment of the moon or something.
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