Normally, the 24-hour background basal rates are preprogrammed and relatively constant from day to day, although temporarily altered rates can be superimposed to adjust for a short-term change in requirement. For example, the basal delivery rate might need to be decreased for several hours because of the increased insulin sensitivity associated with strenuous activity.
Boluses are used to correct high blood glucose levels and to cover mealtime insulin requirements based on the carbohydrate content of the food and concurrent activity. Bolus amounts are either dynamically programmed or use pre-programmed algorithms. When the boluses are dynamically programmed, the user calculates the dose based on the amount of carbohydrate consumed and the current blood glucose level. Alternatively, the meal or snack dose algorithm (grams of carbohydrate covered by a unit of insulin) and insulin sensitivity or blood glucose correction factor (fall in blood glucose level in response to a unit of insulin) can be preprogrammed into the pump. If the user enters the carbohydrate content of the food and current blood glucose value, the insulin pump will calculate the most appropriate dose of insulin. Advanced insulin pumps also have an “insulin on board” feature that adjusts a high blood glucose correction dose to correct for residual activity of previous bolus doses.
The traditional pump (by MiniMed, Animas, Roche, Sooil)— which contains an insulin reservoir, the program chip, the keypad, and the display screen—is about the size of a pager. It is usually placed on a belt or in a pocket, and the insulin is infused through thin plastic tubing that is connected to the subcutaneously inserted infusion set. The abdomen is the favored site for the infusion set, although flanks and thighs are also used. The insulin reservoir, tubing, and infusion set need to be changed using sterile techniques every 2 or 3 days. Currently, only one pump does not require tubing (OmniPod, Insulet). In this model, the pump is attached directly to the infusion set (electronic patch pump). Programming is done through a hand-held unit that communicates wirelessly with the pump.
Optimal use of these devices requires responsible involvement and commitment by the patient. Insulin aspart, lispro, and glulisine all are specifically approved for pump use and are preferred pump insulins because their favorable pharmacokinetic attributes allow glycemic control without increasing the risk of hypoglycemia.
A mechanical patch pump (V-Go, Valeritas) designed specifically for patients with type 2 diabetes is available on a basalplus-bolus insulin regimen. The device is preset to deliver one of three fixed and flat basal rates (20, 30, or 40 units) for 24 hours (at which point it must be replaced), and there is a button that delivers two units per press to help cover meals.
D. Inhaled Insulin