Insulin pump in adult patients with diabetes mellitus

I have never used an insulin pump in adult patients with diabetes mellitus. One of my patients is asking for this device, and I would appreciate information about dose calculations and what to tell the patient before beginning use of the pump.
—— MD

Starting insulin pump therapy is essentially the same in all patients. Once you have selected a pump, contact the manufacturer. All pump companies have clinical specialists to assist patients with start-up of their pump.

Dosage calculations are based on pre-pump insulin dosages. Calculate the total daily dose of all types of insulin the patient has been using. If a patient has been using a sliding scale for coverage, estimate the average amount used per day to calculate the total daily dose (TDD).

To calculate the patient’s initial basal rate for the pump, reduce the TDD by 25% and divide the remainder into 2 equal quantities (one half will be used to calculate the basal rate, and the other half will be used for the bolus amounts). The basal rate is half of the TDD remainder (after 25% has been deducted), divided by 24. Written as a mathematical formula, this becomes: basal rate = [(0.75 x TDD) ÷ 2] ÷ 24. These calculations give an initial basal rate. We generally use one basal rate for the entire day and adjust it later.

Patients will administer insulin boluses based on blood glucose readings and food intake. To determine bolus amounts, first calculate insulin sensitivity and carbohydrate/ insulin ratios. To calculate the sensitivity to insulin (ie, the amount by which 1 unit of insulin will decrease the patient’s blood glucose level), divide 1800 by the TDD. To calculate the initial carbohydrate ratio (the number of grams of carbohydrate that 1 unit of insulin will “cover”), divide 500 by the TDD. The formula for the amount of a correction bolus (administered to correct an elevated blood glucose level) is: [(current blood glucose level) - (target blood glucose level)] ÷ (insulin sensitivity). The formula for a meal bolus is: (total grams of carbohydrate) ÷ (carbohydrate ratio). Adding these 2 amounts together yields the total bolus to be administered at mealtime.

Patients who use an insulin pump should be doing true carbohydrate counting, not just counting exchanges. If you are not comfortable teaching carbohydrate counting, refer patients to a dietitian before the start of pump use. Some physicians switch patients to a basal/bolus routine that involves use of a long-acting and a rapidacting insulin before they initiate pump therapy; this gives the patient an opportunity to become familiar with carbohydrate counting and coverage. In addition, many pump companies teach carbohydrate counting as part of the pre-pump training they provide.

Let patients know that although fewer injections are needed when they use an insulin pump, they may be required to perform more finger sticks for blood glucose monitoring. Many patients who use a pump check their blood glucose level 8 to 10 times a day. Patients often ask what the benefit of the pump is if they have to check their blood glucose level that often. I tell them that the pump can allow them more freedom in the management of their diabetes, that they will be less tied to set mealtimes and schedules, that use of the pump often eliminates nocturnal hypoglycemia, and that it can stabilize blood glucose levels.

—— Kathy MacNeill, RN, CDE
Associate Director, Diabetes Master
Clinician Program
Heartland Rural Health Network
Avon Park, Fla