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The Beginner's Level
The first step in using an insulin pump successfully is finding a basal rate or rates that will keep the user's blood sugars level while he is not eating. When one begins using a pump, setting, testing, and resetting the basal rate is often needed to determine the best rate through the day. The current MiniMed model offers five to six different basals each day, while the Disetronic offers 24 individual rates-a new one every hour-if desired.
Changes in the basal rate can be used for various parts of the day, such as raising the rate around 1 or 2 am until 9 or 10 am to cover a Dawn Phenomenon. Most often, a pumper will end up having better control when changes to the basal rate are no more than 0.2 units per hour above or below their average daily rate, and when their daily basal insulin delivery is close to 50% of their total daily insulin dose. Approximately 70% of pump users have some degree of the Dawn Phenomenon. Figure 1 shows the basal pattern that John most commonly uses with these people.
Once a beginner, with the help of his health care team, has found the basal rate or rates that hold him stable, he usually "lets well enough alone." This is smart, especially since the boluses given for carbohydrate and high blood sugars are varied to match changing daily lifestyle factors. A pumper changes boluses to match the amount of carbohydrate he will eat, with additional adjustments based on the current blood sugar reading. So for a beginning pumper, the general rule is a steady basal or basals, while changing boluses to meet daily needs.
The Graduate Level
But like the freedom of driving an Austin-Martin along winding country roads, insulin pumps have additional options on the daily path to good control. Once a pumper has used the "stable basals, varied boluses" method long enough to achieve good control, it may be time to graduate to a higher level of control and competence.
This graduate level involves learning when to change the basal rate to match unusual needs. Here, basal changes are made to match specific situations that the person's experience has shown often lead to a loss of control. Remember though, not everything that leads to a loss of control can be addressed with a changed basal rate!
Timing is really the key in understanding how to tap the advantages of changing basal rates for better control. The timing of a change in the basal rate is usually as or more important than the amount of the change. Due to the slow impact that basal rate changes have on the blood sugar, raising and lowering the basal rates is quite different from changing boluses (see Figure 2). For instance, when a bolus for a meal is given, that insulin is delivered as a pool under the skin in a matter of a couple of minutes. This bolus will start to work in about 15 minutes and peak in activity in about 3 hours.
Due to the quick increase in the size of the insulin pool when boluses are given, they work faster than raising the basal rate. As noted, a 2.0 unit bolus will have a decided effect on the blood sugar inside of 3 hours, but a rise in the basal rate of 0.2 units an hour won't have a similar effect until 7 or 8 hours have passed. For this reason, basal rate increases are not used to treat random high blood sugars.
Think of it as a savings account. You can put a $1000 into a savings account today and begin to see earnings increase immediately, or you can place a dollar a day into the account and see the same gain in a little over 3 years. Increases (and decreases) in the basal rate are like the dollar a day method, with their effect on the blood sugar just beginning to occur 2 to 3 hour later, compared to 20 or 30 minutes with a bolus.
Raising and lowering the basal rate has to be done 2 to 3 hours before their effect is desired. The impact can be the same in the long run, but advanced planning is required. But this type of planning is very useful in situations where smaller increases or decreases in insulin levels are desired. The examples below are situations where control problems can arise when only the beginner's level is used. Suggestions are provided regarding ways to change the basal rate to help in maintaining control.
Although exercise improves health, it can easily lead to insulin reactions when it is intense or prolonged. To prevent lows during and after most exercise, it is NOT necessary to lower the basal rate, especially when exercise lasts 45 minutes or less. For regular, short periods of activity, the blood sugar can be maintained with extra carbohydrate intake and some reduction in a bolus prior to exercise.
But when exercise lasts longer or when physical tasks like spring cleaning or reroofing a house are performed, the basal rate can be reduced by 25% to 40% starting 2 hours before the activity begins. Following physical activities that last 90 minutes or more, some ongoing reduction in basal rates (10% to 25%) may be needed over the next 24 to 36 hours. Careful blood sugar monitoring is required during these hours to be aware of the extended blood sugar lowering effects from the activity.
Usually boluses are used to cover the carbohydrate content of foods. But what if you plan to attend a brunch over two to four hours, or a street fair with snacks at 10 different food booths, or an evening of parties with several hours of snacks? Adjusting the basal upward is ideal for this time of extended grazing. Calculations are required for success. For instance, a rise in the basal rate of 0.5 units per hour over 4 hours will deliver 2.0 units of insulin, while an extra 1.0 unit an hour for the same period will deliver 4.0 units of extra insulin. Rarely is a rise in the basal rate this extreme. This type of substantial increase in basal insulin delivery begins to act more like a bolus. This larger-than-normal increase in the basal insulin would be timed to start 60 or 90 minutes before the grazing begins.
Normal Bedtime Reading
The goal in good control is a normal blood sugar, but what if this happens at bedtime? Normal bedtime readings often mean that too much insulin is active and an insulin reaction is likely during sleep. The Unused Insulin Rule in Chapter 12 of Pumping Insulin covers how to judge how much insulin is left to work in these situations for more accurate compensation.
Normally a large bedtime snack would be needed to offset this insulin and prevent an insulin reaction. An alternative for the weight conscious, however, is to eat less but lower the basal rate over the next hour or two to reduce the amount of active insulin. However, the basal should never be reduced to less than 50% of the normal rate for any time longer than two hours, as this can lead to an insulin deficient state and the possibility of ketoacidosis. With this method, checking the blood sugar two hours after bedtime is strongly recommended the first few times this is done to ensure that the blood sugar dose not go low or high during the night.
Spikes Between Meals
Blood sugars that temporarily spike between meals but return to normal before the next meal often indicate that a bolus was not given soon enough before the meal or that the carbohydrates in that meal were rapidly absorbed with too little insulin in the blood. One way to reduce these post meal spikes is to raise the insulin level ahead of time by raising the basal rate before eating begins.
Spiking most often occurs after breakfast due to more insulin resistance at this time of day and after the evening meal due to its size. Occasionally, a pumper will experience this rise after lunch as well. To greatly reduce post-meal spiking, raising the normal basal rate by 0.1 or 0.2 units per hour works great. The timing of the increase depends on which meals are a problem. When this method is used, of course, the corresponding meal bolus has to be lowered, and, if this meal is skipped, some snacking will be required to offset the higher basal insulin.
Low Glycemic Index Foods
Regular insulin is really too slow for most meals. To deal with this, the pumper takes boluses 30 or 45 minutes before the meal to control post-meal blood readings. However, some meals that contain beans and certain types of pasta have a low glycemic index. These meals will create a slow, gradual rise in the blood sugar. When Regular has been taken for a burrito or a plate of lima beans, an insulin reaction may occur a couple of hours later due to the slow digestion of this type of carbohydrate. The blood sugar may rise later as digestion takes hold. On a pump, it's easy to take a split bolus-half before and half two hours later to cover this slower carbohydrate.
Another way to handle this situation is to skip the meal bolus but raise the basal insulin delivery for a three to six or eight hour period following the lower glycemic index meal. Again, additional monitoring is advised the first few times this is attempted.
Since only Regular insulin is used in a pump, fast changes can be made in insulin doses to match unanticipated changes in lifestyle. Insulin adjustments are normally made each day in relation to carbohydrate intake and activity. But in unusual circumstances pumps can really show their stuff using these and other adjustments in the basal rate. Think about how these suggestions might benefit your own control, but always discuss any change in insulin doses with your physician before implementing it.
Lower Basal Rate
Increase Basal Rate
Diabetes Health is the essential resource for people living with diabetes- both newly diagnosed and experienced as well as the professionals who care for them. We provide balanced expert news and information on living healthfully with diabetes. Each issue includes cutting-edge editorial coverage of new products, research, treatment options, and meaningful lifestyle issues.