The FDA has reported that in 2007, 375,000 Americans with diabetes were using an insulin pump.1 Improvements in pump technology (including the addition of continuous glucose monitoring2,3), more data on the use of pumps in type 2 diabetes,4-7 improved insurance coverage,8 and the general population’s comfort with technology-based solutions may lead more patients with diabetes to choose a pump to deliver their insulin.
As a result, primary care practitioners will be increasingly likely to have patients who use continuous subcutaneous insulin infusion (CSII) pumps. While the initiation of pump therapy and follow-up with patients who use pumps have traditionally been the purview of endocrinologists, it is important for primary care providers to understand the basics of insulin pump therapy, enabling them to work collaboratively with the patient and the diabetes care team.
REVIEW OF INSULIN ACTION IN THE BODY
The body’s own (endogenous) insulin is secreted by the beta cells of the pancreas. Basal insulin is the background amount of insulin continuously released by the body in order to regulate hepatic glucose production and lipolysis. In response to food intake, the body releases additional insulin to match the glycemic effect of carbohydrates, fat, and protein.9
Insulin regimens attempt to mimic the body’s physiologic release of insulin by administering long-acting insulin to provide basal coverage, and rapid- or short-acting insulin to metabolize meals. The first long-acting insulin developed was NPH (still in use today), which was created by the addition of neutral protamine Hagedorn to regular insulin to delay insulin absorption.10
There are a few reasons that NPH use has fallen out of favor, especially for patients with type 1 diabetes, who do not produce endogenous insulin. One is a pronounced peak in action that requires patients to time their consumption of meals and snacks around peaks. If food consumption is insufficient, hypoglycemia may occur. Additionally, after the peak follows a valley in which low levels of exogenous insulin can lead to hyperglycemia.11
The second problem with NPH surrounds the inconsistency in both intersubject and intrasubject absorption rates. Absorption variability as great as 50% has been reported.12,13 This, of course, may lead to an increase in glycemic variability, that is, the magnitude of glucose fluctuation14 within a day. (Note: It has been hypothesized that, in conjunction with the A1C measure, glycemic variability may account in part for the long-term complications of diabetes.14)
Insulin Analogs
Radical advances in the potential for improved glucose control emerged with the development of insulin analogs.15,16 On the market now are three rapid-acting insulin analogs: lispro, aspart, and glulisine. Long-acting analogs are glargine and detemir, either of which may be given once or twice a day.17 Clinically, detemir is generally given twice per day in most patients with type 1 diabetes due to its shorter duration of action.
Most patients with type 1 diabetes are now managed with a once- or twice-daily injection of a long-acting insulin analog and one short-acting analog before each meal; thus, patients must take four or more insulin injections each day. While this multiple daily injection (MDI) insulin regimen approximates the body’s endogenous production of insulin more closely than the traditional split/mix regimens of NPH and regular insulin, there are still shortcomings. Once the long-acting insulin has been injected, it provides a steady level of insulin that cannot be adjusted for changes in the patient’s routine, such as exercise, delayed meals, or sleep, or for changes in the metabolic milieu, such as infection or other illness.18
PUMP BASICS
The CSII pump is a programmable insulin delivery system that provides continuous amounts of insulin and allows the user to deliver extra insulin to metabolize meals or to correct high blood glucose levels. Typically, rapid-acting insulin is used in the pump, although for patients with severe insulin resistance who need high doses of insulin, U-500 regular insulin may be used.19 U-500 regular insulin is a concentrated insulin dosed at one-fifth of U-100 regular insulin; that is, 100 units of regular insulin would equate to 20 units of U-500 insulin. (To clarify further, “U-100” refers to 100 U/mL, and “U-500” means 500 U/mL.) Understanding the indications for U-500 insulin and its adjustment is a specialized skill of the diabetologist experienced in its use.
A traditional pump consists of a beeper-sized device. It contains a reservoir that the user fills with insulin, then connects to an infusion set. The infusion set consists of tubing connected to a flexible catheter or needle that is inserted into the subcutaneous tissue. A mechanism to attach and detach the tubing from the infusion site is included so that users can disconnect it for bathing, sexual activity, contact sports, or other circumstances. Infusion sets are available in different sizes and styles to accommodate patients with different body weights, body fat levels, and lifestyle needs.