While pumps are sophisticated and precise, they still interface with a human user.
Richard Millstein, DO
Department of Endocrinology, University of Colorado, Denver
Nancy Mora Becerra, MD
Division of Endocrinology, Diabetes & Metabolism, The Ohio State University Wexner Medical Center, Columbus, OH
Jay H. Shubrook, DO
Director of Diabetes Services, Primary Care Department and Professor, Touro University College of Osteopathic Medicine, Vallejo, CA
Address: Jay H. Shubrook, DO, Primary Care Department, Touro University College of Osteopathic Medicine, 1310 Club Drive, Vallejo, CA 94592; e-mail: firstname.lastname@example.org
Dr. Shubrook has disclosed consulting and research for AstraZeneca, Eli Lilly, Novo Nordisk, and Sanofi.
ABSTRACTInsulin pumps are a major advance in diabetes management, making insulin dosing easier and more accurate and providing great flexibility, safety, and efficacy for people who need basal-bolus insulin therapy. They are the preferred treatment for people with type 1 diabetes and many with type 2 diabetes who require insulin. This article reviews the basics of how insulin pumps work, who benefits from a pump, and how to manage inpatients and outpatients on insulin pumps.
The advent of the insulin pump in the late 1970s was a step forward in diabetes treatment,1 and recent improvements make these devices easier to use in intensive insulin management. Today, more than 400,000 people in the United States are thought to be using an insulin pump.2
With a pump, patients can adjust the dosage and discreetly give themselves boluses by simply pushing a button instead of giving themselves multiple daily injections. Also, pump therapy can be tailored to correct for hepatic glucose production in a way that injections cannot.
This article reviews the clinical application of continuous subcutaneous insulin therapy—ie, the insulin pump—and provides recommendations for patient selection and management.
INDICATIONS FOR AN INSULIN PUMP
The American Association of Clinical Endocrinologists3 recommends considering an insulin pump for patients with type 1 or 2 diabetes mellitus who have a clear indication:
WHO IS A GOOD CANDIDATE FOR AN INSULIN PUMP?
Good candidates for a pump are patients with type 1 diabetes (and some with type 2) who are well versed in taking multiple daily injections, are already checking their glucose four or more times daily, “counting carbs” (estimating or, preferably, measuring how much carbohydrate they are eating, and limiting their intake accordingly), and demonstrate the ability to adjust their dosing appropriately (Table 1).
A pump is not a shortcut to checking glucose less frequently or making fewer decisions. However, for those who actively manage their diabetes, it provides more real-time flexibility and some important safety features, as discussed below.
IS A PUMP BETTER THAN INJECTIONS?
Several studies have compared insulin pump therapy and multiple daily injections.4–7 While some found no difference in glucose control in terms of hemoglobin A1c or hypoglycemia, others showed improved glucose control with pumps in patients who had higher baseline hemoglobin A1c levels (> 10%).6 In this subgroup, a pump lowered hemoglobin A1c an additional estimated 0.65% compared with multiple daily injections.6 Fructosamine levels also improved in pump users.6
Using continuous glucose monitoring for 3 days in a study in children with type 1 diabetes, Schreiver et al8 found lower insulin requirements and less-severe glycemic excursions with a pump than with multiple daily injections.
A 2013 study9 of 57 patients ages 13 to 71 with type 2 diabetes who were struggling to control their blood sugar with multiple daily injections found that they achieved better control with less insulin using a pump.
A meta-analysis found pump therapy to be more effective than multiple daily injections for those who used it more than 1 year.10
ADVANTAGES AND DISADVANTAGES OF INSULIN PUMP THERAPY
Intensive glucose control reduces microvascular complications in type 1 diabetes.11–14 The advantages of using a pump include better adherence, more accurate dosing, greater lifestyle flexibility, control of the dawn phenomenon without induction of nocturnal hypoglycemia, and the ability to suspend or temporarily reduce basal insulin to compensate for increased physical activity.15
Disadvantages include the high degree of technical aptitude required, the need for high-level engagement, skin reactions to tape, a higher risk of diabetic ketoacidosis from pump malfunction, infusion-site problems such as “tunneling” of insulin (leakage of insulin along the outside of the cannula and back to the skin surface) and clogging of the infusion set, and a risk of inactivation of insulin from exposure to heat, which can lead to ketoacidosis in a few hours if not addressed promptly.15
IS IT COST-EFFECTIVE?
There is evidence that continuous subcutaneous insulin infusion is cost-effective, both in general and compared with multiple daily injections for children and adults with type 1 diabetes mellitus. Cohen and Shaw16 found that life expectancy and quality-adjusted life-years increased in pump users, although the price per life-year gained varied greatly depending on the model used.
And this therapy is expensive. Most pumps cost more than $6,000, and supplies cost about $300 per month. Most insurance providers cover this therapy for patients with type 1 diabetes (Table 2) but less often for those with type 2. Further, many insurance policies have copayments, and patients may find a 20% co-payment a significant financial burden. Physicians need to obtain preapproval for insulin pumps from the insurance company. Typically, prescriptions for supplies are written annually. Despite these significant costs, most patients with type 1 diabetes who use an insulin pump find that the benefits of improved control and greater independence justify the cost.
An annual review of currently available insulin pumps and other diabetes-related equipment is published in Diabetes Forecast.17
PATIENT PERSPECTIVE ON INSULIN PUMP USE
Many patients who use a pump find that it gives them greater flexibility to adjust to day-to-day changes in schedules and routines. For example, consuming an extra serving at a meal could necessitate another injection for a patient on multiple daily injections, but a pump user would need only to push a few buttons. With cell phone apps available to control some pumps, many people find that an insulin pump is more discreet and easier to manage than carrying around injection supplies. Further, the complex calculations of carbohydrate ratios and correction factors are easier and more accurate with a pump.
In an open-label randomized study,18 29 of 41 patients with type 1 diabetes said they preferred a pump to multiple daily injections.
Conversely, some people do not want a pump because it is attached all the time and identifies them to others as having an illness. Other patients do not trust a machine and want control in their own hands. (Actually, machines typically are much more reliable and less mistake-prone than humans.)
HOW DOES A PUMP WORK COMPARED WITH MULTIPLE DAILY INJECTIONS?
Patients taking multiple daily injections must use two types of insulin: a long-acting one that reaches a steady level in the blood without a peak and lasts from 12 to 24 hours, and a rapid-acting one taken with meals, usually having a peak of action and an effect lasting 3 to 5 hours. The idea is to approximate normal insulin patterns, with a basal level in the background and peaks (boluses) of insulin with carbohydrate intake.
Insulin pumps use only one kind of insulin—a rapid-acting one, ie, lispro, aspart, or glulisine. They preserve the basal-bolus concept, but with many refinements (discussed below).15
Most pumps are attached to the patient by plastic tubing that connects the reservoir to a subcutaneous cannula or steel needle. However, some pumps have a reservoir directly attached to a subcutaneous cannula without the tubing. This type of pump is controlled with a remote device.
The infusion set and the site should be changed every 3 days
The infusion set (cannula or needle and tubing) and the site should be changed every third day to minimize the risk of infection and abnormal delivery due to protein buildup on the cannula os, epithelial healing, and irritation around the site. Failure to do so often results in higher blood glucose concentrations.19
The patient and healthcare team work together to calculate the patient’s daily insulin needs, and the pump is programmed based on the patient’s requirements, lifestyle, and sensitivity to insulin. Once the pump is started, the patient operates it to deliver the insulin dose according to carbohydrate intake and blood glucose level.
The basal rate is programmed by the physician and is intended to mimic physiologic insulin release. The pump can be set to a number of basal rates within any 24-hour period. This provides more physiologic matching of insulin delivery to hourly insulin needs based on the patient’s daily schedule.
If the patient has been taking multiple daily injections, the hourly basal rate can be calculated by dividing the daily basal dose by 24. However, lower rates are usually used after midnight, and rates are increased early in the morning to counteract the dawn phenomenon.
The rates can also be adjusted temporarily (for up to 24 hours), with a feature called the temporary basal rate. People tend to have higher blood glucose levels when they have a respiratory illness, are under significant stress, or are menstruating. Thus, a person with influenza could increase the basal rate by 25%, or a student could run a temporary basal rate of 150% for 4 hours before taking a final exam.
Conversely, exercising increases insulin’s effectiveness at the muscle level, and insulin requirements drop. To counteract this, one would temporarily decrease the basal rate in the pump before exercising.
A pump is not a shortcut to checking glucose less frequently, or to making fewer decisions
A bolus of insulin is given for meals and to correct hyperglycemia, as with multiple daily injections. A pump calculates the bolus based on the carbohydrate ratio, correction factor, or both. These ratios are programmed into the pump by the physician. A benefit of the insulin pump is that the patient just has to input the amount of carbohydrates to be eaten or record a blood glucose level and the pump will calculate the bolus dose of insulin to be given.
The carbohydrate ratio is the amount of insulin that should be taken per amount of carbohydrate. A typical ratio is 1:15, meaning that the patient should take 1 unit of insulin for every 15 g of carbohydrates to be eaten. This varies by patient depending on insulin sensitivity.
The correction factor describes how much the glucose level is expected to drop per unit of insulin given. For example, if the target glucose level is 100 mg/dL and the correction factor is 25, then the patient will get 1 unit of correction of insulin if his or her glucose level is 125 mg/dL, 2 units if it is 150 mg/dL, and so on. A pump can dispense fractions of a unit.
The target glucose level or range is set by the physician and patient and is one of the factors the pump uses in calculating a bolus dose. Insulin pumps allow for multiple target glucose levels. Commonly, to minimize the risk of hypoglycemia, a higher (less strict) target is set for bedtime and overnight than for daytime.
Active insulin time defines how soon the patient can take another bolus.
Often, people eat more than they thought they would. They may also find that the glucose level did not increase or decrease as much as expected. Many patients who actively manage their glucose take additional boluses of insulin after a meal if their glucose is higher than they thought it would be. A patient taking injections cannot know how much of the insulin from the before-meal bolus is still working and has to guess.
Insulin pumps use a logarithmic formula to calculate this and prevent the user from “stacking” insulin boluses and lowering the glucose level too much. For example, if the active insulin time is 4 hours and the patient took a bolus for lunch at noon, he or she would be unable to take a full insulin correction dose until 4:00 pm. The patient can override this feature. Although the active insulin time varies from patient to patient, it is rarely more than 4 hours.
Suspend. When a person who is taking insulin injections starts to experience hypoglycemia, he or she has one option—to eat something to treat the low blood glucose. The insulin injection has already been taken and cannot be reversed. However, with an insulin pump the patient can first suspend the pump so that no additional insulin is infused until it is safe again, and then eat to treat the low sugar level. This allows the patient to eat less, prevent overtreating, and, hopefully, prevent rebound hyperglycemia.
Reverse correction. When patients take insulin for an upcoming meal, they estimate the amount needed for the carbohydrates that they are about to eat as well as how much correction is needed. If their glucose level is below the target range, they may or may not subtract insulin from the dose to achieve the glucose target. The pump does this automatically, resulting in a lower dose of insulin for that bolus. This allows the patient to take a bolus for a meal even if he or she is below the target, and thus prevent hyperglycemia.
While pumps are sophisticated and precise, they still interface with a human user.
Take into account the patient’s age, life expectancy, concurrent illnesses, risk of hypoglycemia, and other factors.