After a bolus is given, insulin continues to affect your glucose level for some time. The amount of insulin left in your bloodstream is referred to as “active insulin” or “insulin on board.” You can set how long you want the pump to track active insulin, but discuss with your health care team how long you should have the pump track it. Generally, people set the active insulin time to two to five hours (most often, three). The pump calculator keeps track of the amount of insulin that is still active from previous boluses so you do not have boluses overlapping each other and dropping your glucose levels (this is referred to as “insulin stacking”).
Maximal Bolus and Basal Rates
You set a maximal rate for both basal and bolus insulin delivery to enhance safety. This prohibits you from accidently taking 20.0 units instead of 2.0, for example.
Pump Bolus Calculators Make Pumps Smart
The pump bolus calculator—which makes pumps smart—calculates how much insulin to give for boluses. It takes into account your insulin-to-carbohydrate ratio (ICR), the insulin sensitivity factor (ISF), the duration of active insulin, and your target glucose range. These values (except active insulin) can be altered by time of day, for example, because your insulin sensitivity and your ICR change over the course of 24 hours. When you first get your pump, your diabetes care team will help you determine these settings. They can be changed at any time (preferably in consultation with your diabetes team) as indicated by the patterns in your glucose control.
To determine the amount of insulin you take for a food bolus, you enter the number of grams of carbohydrate you plan to ingest and your current blood glucose level. Then the pump calculator will determine how much insulin you should take. If your blood glucose is above or below your target range, the bolus calculator will also figure out if you need to add or subtract insulin from the food dose.
However, you can always alter the insulin bolus dose suggested by the pump bolus calculator, giving yourself less or more insulin depending on any number of factors. If you are about to exercise or are not sure you will eat an entire meal, you might want to decrease your bolus from what the calculator suggests. If you have ketones or are sick, you might want to take more. Although it is convenient to have the pump calculator so you don’t have to do the calculations yourself, it is important to think before you push the button.
Here’s an example. If your blood glucose is 250 mg/dL and you are about to eat 15 grams of carbohydrate for lunch, you would enter those numbers into your bolus calculator (or the blood glucose would be automatically sent from your meter). The calculator suggests an amount of insulin to bring your glucose into your target range and cover your meal. Some pumps will show you the two different amounts, one for food and one for correction, and others will simply lump them together into one suggested bolus without showing a breakdown.
Keeping detailed records of your blood glucose levels, doses of insulin, food intake, and other events (such as exercise, illness, or stress) is important. It is also hard to keep a logbook or a record of all that you do every day. However, when this information is available for review, you are able to spot patterns and trends that may be problematic. In contrast, if you are looking only at your current glucose level, you won’t detect these patterns, even if you correct your high glucose nearly every morning and treat a low every afternoon.
By uploading data from your pump to the software, especially when it also includes information from your glucose meter (and a CGM, if you have one), you are able to review up to three months of data. Because the bolus calculator captures the carbohydrate history for meals and breaks out the bolus details so you can see when correction doses were administered, you have the ability to look for trends and patterns. By reviewing these data, you can identify what the problems are, why they are occurring, and how they can be fixed.
A Diabetes Meeting
The purpose of a diabetes meeting is to sit down with your diabetes team and review your glucose trends and patterns, your pump (and CGM) settings, and how you are doing with your diabetes regimen. The frequency should be weekly, or less often if there are no issues with your diabetes. The purpose of a diabetes meeting is to identify patterns and trends in your glucose levels, alterations that need to be made in your pump (and CGM) settings, or behaviors that you are looking to improve, such as remembering to bolus, measuring blood glucose levels, using the bolus calculator, and changing infusion sets at least every three days, and more. Set goals, monitor your progress over time, and reward yourself for achieving your goals. After you review your information, discuss it with someone—a friend, spouse, child, parent—and, if needed, with your health care team.
Interpreting Data
There are several ways to look at your pump or meter data. These include a logbook, trend graphs, pie charts, and data tables. The logbook is just a digital version of a handwritten log. Trend graphs, pie charts, and data tables are visual representations of the logbook information that make it easier to spot patterns and trends. The trend graphs and pie charts are colorful visual representations of your glucose numbers, averages, and high/low patterns, whereas the data table contains just numbers and values. Each method of displaying your information can be reviewed to identify specific problems or times of good control.
Logbooks
Logbooks, like the paper ones you were first given when you were diagnosed, are grids containing all of the pertinent information that affects your diabetes. They are either very detailed or they can just display your glucose values at certain times of day (before or after meals).
Trend Graphs
A trend graph is often the first thing that your diabetes team will look at because they easily show many days of data laid over each other. A trend graph has your blood glucose values along the vertical axis and the time of day along the horizontal axis. The horizontal axis generally shows 24 hours and can start at either 5:00 A.M. or midnight, depending on which pump, CGM, or meter you use. Customizable target ranges can be set and are shown as a shaded horizontal bar through the whole graph. Multiple days are represented on the graph as different colored lines with small symbols at each blood glucose value. On a CGM graph, the colored lines are more fluid, with no individual symbols because there are many, many more data points. There is usually also a dotted line that runs through the graph as an average of all the days’ values.
Trend graphs make it easy to spot repeating patterns. Trend graphs are also helpful because you can see your highest and lowest values on the graph, and with the adjustable target range you can also see how often your values swing outside this range.
The graph generated by CGM shows a spike of numbers beginning around 4:00 A.M. This graph offers a good visualization of the dawn phenomenon (it is circled in the graph below). The dawn phenomenon occurs when certain hormone levels, such as cortisol and growth hormone, spike in the early morning hours, resulting in increased blood glucose levels, which in turn requires a higher insulin dosage. Looking at this graph will help you identify the dawn phenomenon and allow you to treat it by increasing your early morning basal rate.
Pie Charts
Pie charts show the averages for the numbers in your target range, above it, and below it. Each pie chart represents a different time of day (e.g., before and after breakfast) or a
