The “patch” or “wireless” pump, as it is sometimes called, is a self-contained unit or “pod” that resides directly on the skin, delivers insulin through a flexible catheter, and is disposed of or recycled every two to three days; it does not require tubing.
Potential pump users have a variety of manufacturers and models from which to choose, all providing similar features. Considerations for selecting a pump should include its particular features, cost of supplies, insurance coverage, customer service and support, and personal preference.
Basal and Bolus Insulin
The continuous background delivery in the pump is known as the basal; the rate at which the pump delivers the basal can be changed at different times of day to allow for changes in the patient’s routine and metabolic milieu (see Figure 1). Basal rates can be set anywhere between 0.025 and 35 units per hour. Most pumps allow for basal rates to last for as little as 30 minutes, but pump users commonly set one to four basal rates over 24 hours.
Some diabetic patients experience the dawn phenomenon, that is, fasting hyperglycemia resulting from the body’s release of growth hormone, cortisol, and adrenaline. These hormones, which produce a state of insulin resistance, are released beginning at about 2:00 to 3:00 am. A patient who is taking 24 units per day of total basal insulin might set a basal rate of one unit per hour; adjustments can be made if the patient needs less insulin at night and is prone to the dawn phenomenon.
All pumps begin basal rate programming at midnight. A basal rate profile for a patient who is prone to the dawn phenomenon and who needs 24 units/d of basal, goes to bed at 10:00 pm, and wakes up at 6:00 am, might look like this:
12:00 am: 0.8 units/h
3:00 am: 1.2 units/h
9:00 am: 1.0 units/h
10:00 pm: 0.8 units/h
Temporary basal rates may be set lower to account for exercise, or higher during times of illness. The pumper selects the amount released, the rate, and the length of time the temporary rate should last. After that selected time period is over, the pump automatically reverts to the regular basal rate. Setting lower basal rates before, during, or after exercise may benefit a patient who experiences exercise-related hypoglycemia. A patient who needs to adjust for exercise might select a temporary basal rate set to begin one hour before exercise and continue during exercise and for one hour after exercise.20
Even with these adjustments, however, low blood sugars may still occur, and delayed hypoglycemia may develop hours after exercise is completed.21 Muscle and liver tissue store excess sugar in the form of glycogen; glycogen stores are depleted during exercise, and blood sugar may decline when the muscle and liver take up blood sugar to replace the stores. In such instances, an extra carbohydrate snack and/or use of the temporary basal may prevent hypoglycemia.20
Setting temporary basal rates may also prevent hyperglycemia. In the absence of sufficient insulin, patients with type 1 diabetes produce ketones. Setting higher basal rates during illness, combined with frequent monitoring of blood sugars and ketones in the blood or urine, can prevent diabetic ketoacidosis (DKA). It is important for patients to understand that illness may increase their metabolic need for insulin.9 Even if the appetite decreases during illness, extra insulin may be needed. Frequent blood glucose monitoring and testing for ketones, when necessary, are essential for the patient with type 1 diabetes.
The supplemental insulin that patients take to compensate for carbohydrate intake and to correct high blood glucose is called the bolus. More recent pump technology, sometimes called the “smart” pump, includes features that will calculate for the patient how much of a bolus should be taken, based on three factors: carbohydrates ingested, current blood glucose level, and active insulin, that is, the amount of insulin that is still considered active after the patient takes a bolus based on the pharmacodynamic profile of the insulin.15,22
Carbohydrate-Counting
By the time a patient is started on an insulin pump, he or she should be proficient in carbohydrate-counting.8 There are several books on the market that list carbohydrate content of foods, including popular restaurant menu items and products sold in supermarkets. There are also apps available for PDAs and smart phones. The American Diabetes Association Web site (www.diabetes.org) offers carbohydrate-counting and menu-planning tools. For patients who eat out, it may be helpful to look up the restaurant’s menu online in advance and if possible, research the nutrition facts associated with each course selection. Even for patients with good carbohydrate-counting skills, it is often a challenge to get blood sugars into a desirable postprandial range.