The rate at which an insulin pump infuses small, “background” doses of short-acting insulin. Over a 24-hour period, the basal flow of insulin accounts for about 50% of a person’s total daily insulin requirement. However, this may vary depending on overall caloric intake or activity level.
Many people use an insulin pump because it closely mimics what a healthy pancreas does: It provides a steady flow of insulin all the time to help the body utilize the glucose that is always in the bloodstream, providing energy for thinking, breathing, and other automatic functions. In addition, a pump allows users to give themselves larger insulin doses (“boluses”) at mealtimes to cover the amount of carbohydrate ingested. This combination of basal and bolus doses helps keep blood glucose levels close to normal at all times, which in the long run can help prevent diabetic complications. (For people who inject insulin, the intermediate- or long-acting insulin serves as the basal insulin, and short- or rapid-acting insulin injections are used to cover meals. The long-acting insulin analog glargine [brand name Lantus] provides “peakless” basal coverage for up to 24 hours.)
Pump users can program the pump to deliver higher or lower basal doses at certain times of day to meet the body’s changing insulin needs. For example, the nighttime release of counterregulatory hormones (such as growth hormone, epinephrine, and cortisol) can cause a rise in blood sugar in the morning called the dawn phenomenon. For this reason, pump users often need to program a higher basal rate in the morning. Usually, only 2–4 different rates are needed during a 24-hour period. One 24-hour sequence of basal rates is called a basal flow pattern, or basal profile.
Pump users may also need to program different basal profiles for specific days. For example, someone who is a sedentary desk jockey during the work week but is active on weekends may need to program two different basal rate profiles—one for weekdays and another for weekends, when the extra activity helps him burn glucose better during the day. People who work different shifts may need to program different basal profiles depending on which shift they’re working on a given day. Some women may need a different basal profile for the days before menstruation, when blood glucose levels often run higher than usual.
In addition, pump users can set temporary basal rates, which they activate during exercise, for example; after the set period of time, the pump automatically returns to the original basal profile.
When first starting insulin pump therapy, your health-care provider will help you determine your initial basal rate and fine-tune your basal profiles through frequent blood glucose self-monitoring. Frequent low blood glucose could indicate that the basal rate on the pump is too high; frequent highs could mean that the basal rate should be increased.