Diabetes healthcare professionals and their patients share a common pursuit — to find an insulin delivery method that will not only promote normal blood glucose levels, but also allow individuals with type 1 diabetes (formerly called insulin dependent diabetes mellitus) to maintain a flexible lifestyle. The 1993 Diabetes Control and Complications Trial (DCCT), a 10-year landmark study, demonstrated that strict blood glucose control in individuals with type 1 diabetes reduced eye, kidney, and nerve disease by approximately 50%. Improved glucose control had beneficial effects whether achieved by multiple daily injections (MDI) or a programmable insulin infusion pump.¹ Ninety-three percent of the participants of the DCCT were followed until February 2005. This study, referred to as the Epidemiology of Diabetes Interventions and Complications (EDIC), showed that intensive therapy can also reduce the long-term risk of cardiovascular disease.² The choice of intensive insulin therapy treatment depends on the wishes of the individual patient and the comfort and competence of the healthcare team with a given technique.³

The insulin pump is an alternative to insulin injections for maintaining normalized blood glucose levels. Insulin pump therapy, also called continuous subcutaneous insulin infusion (CSII), evolved in research settings during the 1970s. CSII provides insulin replacement in a manner that approximates normal physiological insulin delivery.⁴ CSII is a nonsurgical insulin delivery system that can improve the quality of life for individuals with type 1 or type 2 diabetes.

A new option for many

Insulin pump therapy provides flexibility for those who are not on fixed eating schedules, such as students, shift workers, individuals working irregular hours, and people traveling across time zones. The insulin pump can provide better glucose control for individuals who experience wide blood glucose swings or hypoglycemic unawareness — a condition that exists when counter regulatory hormones, such as glucagon or epinephrine, fail to respond to low blood glucose levels.

Special candidates for insulin pump therapy are individuals with type 2 diabetes who require insulin, women with type 1 diabetes who are considering pregnancy, and children. Studies confirm that at the time of diagnosis of type 2 diabetes, 50% of beta-cell function has already been lost. The earlier that insulin is prescribed, the better for preservation of beta-cell function. In type 2 diabetes, patients can require inordinate amounts of insulin due to insulin resistance and loss of beta-cell function. With pump therapy, initial dosing of insulin can be as much as 50% of the multiple daily injection (MDI) dose. Medicare will reimburse for pump therapy if the patients meet certain criteria.⁵ Pump therapy may assist pregnant women to keep their blood glucose levels in a normal range, thus reducing first trimester congenital malformations and premature delivery associated with macrosomia (large baby). In addition, the hypoglycemia that occurs during morning sickness can be managed more effectively with pump therapy. According to one investigator, women who choose pump therapy as an option during pregnancy have shown to have similar glycemic profiles as women without diabetes.⁶ CSII is used with both children and adolescents. Studies have shown that this population had better glucose control with pump therapy versus MDI.⁷

Any person who expresses a desire to pursue intensive insulin therapy to retard or prevent complications should be evaluated for CSII. Some people may not be able to adhere to the restrictions imposed by intensive therapy with multiple daily insulin injections, and CSII may be a valuable alternative.

Pump mechanics

The insulin pump is an external, battery-operated device that is designed to deliver fast-acting insulin (Novolog, Humalog, Apidra) in specific, programmed doses. It is lightweight and the size of a beeper.⁴ The user inserts a syringe containing insulin into a reservoir in the back of the pump. A 24- or 48-inch long plastic, flexible tube is connected to the syringe. The infusion set consists of a 6 mm, 9 mm, 13 mm, or 17 mm Teflon catheter located at the tip of the tubing.

The pump user changes this set every two to three days. The needle portion of the infusion set is inserted into the subcutaneous tissue of the abdomen (most often used), buttocks, or thigh, and the site is covered with a transparent dressing. The pump is equipped with an alarm system that alerts the user to motor malfunction, an empty or obstructed infusion set, or low batteries.

Once secured to an undergarment, a waistband, or in a pocket, the pump doesn’t alter the wearer’s ability to perform activities of daily living. During sleep the 24- or 48-inch long tubing allows the user to place the pump under a pillow. Pump users can shower, swim, play sports, or engage in sexual activity. Temporary disconnection from the pump is often advised. If the insulin infusion is stopped for more than 90 minutes, the user may need to compensate with additional insulin boluses.

Programming the pump

The insulin pump is programmed to deliver a basal rate (the continuous insulin infusion rate) and bolus dosage (the intermittent infusion rate). The basal rate is the amount of insulin that the body requires in a fasting state, or the constant insulin rate delivered over a 24-hour period, starting at midnight.

Basal insulin via the insulin pump takes the place of the conventional intermediate-acting insulin (NPH, Lente) or the peakless long-acting insulins Lantus or Levemir. The pump can be programmed to deliver from 0.025 units to 10 units of insulin per hour of a fast-acting insulin such as Humalog, Novolog, or Apidra. The average basal infusion rate ranges from 0.4 to 1.0 unit per hour. Novolog and Humalog are indicated and approved by the Federal Drug Administration (FDA) for insulin pump therapy. The user can program the pump to deliver a lower basal rate to compensate for more activity. Basal rates vary during illness, stress, and menstrual cycle. Through meticulous blood glucose monitoring and recording, the user can identify blood glucose patterns and adjust the basal rates accordingly after a healthcare provider sets an initial rate.

The bolus dosage is the amount of insulin programmed to be delivered at least zero to 15 minutes before eating. The timing of insulin is dependent on the individual response to insulin. People with gastroparesis (delayed gastric emptying) can bolus after eating with Humalog or Novolog and still maintain postprandial blood glucose control or extend a bolus. This is a special program that the pump is designed to accommodate.

The bolus dose is matched to the amount of carbohydrates to be consumed at that time. The bolus dose may vary from meal to meal and from day to day. If the blood glucose is less than 50 mg/dl, the pump user can take the bolus after eating. On the other hand, when the blood glucose levels are 140 mg/dl or greater, the pump user will bolus with Humalog or Novolog 15 to 30 minutes before eating a meal.

The starting basal insulin requirements can be calculated by two methods. The first technique uses a standard formula based on body weight of 0.1 unit/pound/day.⁸ For example, a person weighing 130 pounds would require a starting basal rate of 0.54 units of insulin per hour.

The second and more accurate means of determining the basal rate uses the total prepump or insulin injection dose given in 24 hours and reduces it by 20% to 25%. However, individuals who receive high doses of insulin by injection before starting CSII may need to have insulin reduced more than 20%. Less insulin is required for CSII because a constant flow of insulin is maintained at all times.

Once the prepump insulin dose is calculated, 50% of that amount is then divided by 24 hours to determine the units of insulin delivered by the pump per hour or the basal rate. The meal bolus comprises the remaining 50% of the total insulin requirement. For example, an initial dose for a person taking 20 units of NPH and 6.0 units of regular insulin before breakfast, and 8.0 units of NPH and 4.0 units of regular insulin before supper — a total of 38.0 units of insulin — would be as follows:

38.0 units - 20% = 30.4 units
30.4 units x 50% = 15.2 ÷ 24 hours =
0.6 units per hour (basal rate)
The remaining 50% will be utilized for meal boluses.

During the first week of pump start-up, adjustments in the basal rate are made after evaluating blood glucose levels throughout a 24-hour period, noting before-meal blood glucose; two-hour postprandial blood glucose; bedtime blood glucose; and 12 midnight, 2 AM, and 4 AM blood glucose levels. Most individuals ultimately require at least three different basal rates: midnight to 4 AM, 4 AM to 10 AM, and 10 AM to midnight. The lowest basal rate is usually delivered between midnight to 4 AM. Coinciding with the release of anti-insulin hormones — cortisol and growth hormone — from 4 AM to 10 AM, insulin requirements are at their highest. After 10 AM, these hormones start to fall again.⁷ However, recent studies have shown that most patients on pumps require at least five basal rates per day.⁹ The basal rate is correct when blood glucose remains constant under fasting conditions. If the blood glucose levels during the fasting state change by 30 mg/dl, the basal rate needs to be adjusted. Adjustments in this rate should be made one to two hours before the change in blood glucose occurs.

The bolus dose or premeal insulin is dependent on the blood glucose level, anticipated meal size (carbohydrate content), and activity level. The bolus provides flexibility in meal timing. If a meal is skipped, the bolus dose is omitted.¹⁰ The initial starting bolus dose is derived from a standard formula and comprises approximately 50% of the total insulin requirement. To determine if the bolus dose is correct, two- to five-hour postprandial blood glucose levels are evaluated.

The Paradigm® pump created by Medtronic Diabetes uses radiofrequency to receive blood glucose levels automatically sent from the BD link meter to the pump. The pump wearer enters the carbohydrate content of the meal in grams and the pump’s Bolus Wizard Calculator® suggests an estimated insulin dose based on the pump wearer’s insulin-to-carbohydrate ratio, any correction needed for high blood glucose, and target blood glucose. The Bolus Wizard Calculator® also accounts for the amount of active insulin still present in the body from the last insulin bolus, which is a feature designed to prevent hypoglycemia caused by stacking insulin doses.

Carbohydrate-to-insulin ratio

Carbohydrate counting is a meal planning approach that is based on carbohydrates as the main determinant of blood glucose levels. One hundred percent of ingested carbohydrates — complex carbohydrates or simple sugars — converts to blood glucose in 20 minutes to 1.5 hours.¹¹ Several weeks prior to pump start-up, individuals are introduced to this concept and can begin to adjust fast-acting insulin taken before meals according to their carbohydrate intake. The carbohydrate-to-insulin ratio is calculated by dividing the total daily carbohydrate intake by total bolus insulin. For example, a person who consumes 340 grams of carbohydrates daily and takes seven units of insulin before breakfast, six units before lunch, and ten units before dinner — a total of 23 units of insulin — has a carbohydrate/insulin ratio of 15 grams of carbohydrates to one unit of insulin. If normal blood glucose levels cannot be achieved with this simple method, controversial method incorporates the effects of protein on blood glucose in the calculation of the insulin bolus dose. For instance, one meat exchange can be counted as five grams of carbohydrates. In addition, pump users should be advised that a high-fat meal can slow absorption and may require additional insulin. Using an extended bolus feature can control high-fat meals on a pump. This feature allows the user to cover food that enters the bloodstream with an initial bolus and then extend the remaining portion of the bolus out for anywhere from three to six hours. Studies have shown that pizza may require additional insulin, and the bolus may need to be extended for six hours.¹² Carbohydrate-to-insulin ratios may not be consistent for all meals. For example, insulin resistance in the morning due to growth hormone secretion can affect the ratio.

A pump user who requires one unit of insulin for every 15 grams of carbohydrates would receive a four-unit bolus of insulin for a meal containing 60 grams of carbohydrates. The individual would raise or reduce the carbohydrate-to-insulin ratio based on two- to five-hour blood glucose levels. Ideally, two hours after eating, the blood glucose should not rise more than 40 mg/dl, and then return to the premeal level in four to five hours. However, the basal rate must be correct before the individual can evaluate their carbohydrate-to-insulin ratio.

Patient selection

A candidate for the insulin pump needs to be evaluated by a diabetes healthcare team. The pump candidate should have access to a certified diabetes nurse educator, a dietitian, and a physician who are familiar with this type of delivery system. Other members of the team may include a social worker or psychologist, a pharmacist, and an exercise physiologist.

The diabetes healthcare team assesses family support, financial assets, motivation, ability to perform pump programming, willingness to monitor blood glucose at least nine to 12 times a day for the first week and four to six times a day thereafter, and the intellectual capacity to calculate carbohydrate-to-insulin ratios. A pump candidate must agree to test urine ketones when blood glucose levels are greater than 250 mg/dl or during times of illness.

Insurance reimbursement is essential because of cost: approximately $6,000 for the pump and $125 for related monthly supplies. Most insurance providers, including many managed care organizations and Medicare, reimburse for these items. The first integrated insulin pump and continuous glucose monitor were approved by the FDA in April 2006. This integrated system contains a sensor, which is a tiny electrode that is inserted under the skin that measures glucose in interstitial tissue. Results are relayed to the pump from a transmitter every five minutes. The blood glucose values are displayed on the pump. The user can also view 3-hour and 24-hour trend graphs. The system also comes with alarms, which alert the user to rising or falling blood glucose levels. The integrated system is designed to alert the user to dangerous hypoglycemia and reduce postmeal hyperglycemia. Pump users must continue to verify blood glucose levels with a standard blood glucose monitor. This technology has helped to improve overall glucose control. Although reimbursement for the transmitter and sensors are not available. Pump companies are now working with insurers to obtain reimbursement. In addition, the Juvenile Diabetes Research Foundation has begun to independently work towards this goal.¹³

Risks of CSII

Comprehensive diabetes education is necessary to teach clients how to respond promptly to problems related to the intensive insulin therapy regimen. The most common problems include skin infection at the insertion site, diabetic ketoacidosis (DKA) due to high blood glucose levels and insufficient insulin levels, hypoglycemia, and weight gain.

To reduce the risk of skin infections, teach pump users to use careful hygienic techniques when changing the infusion set. They are advised to replace the set every 48 to 72 hours in the morning before breakfast and to report any site redness or discharge to their healthcare provider. The incidence of skin infections has been greatly reduced since pump manufacturers have introduced an antibacterial dressing to cover the insertion site. Pump users are advised to try different tapes and occlusive dressings prior to pump start-up to rule out any allergic response.

For unexplained blood glucose of greater than 250 mg/dl and to minimize the risk of DKA, instruct pump users to periodically inspect the tubing for air bubbles. If levels still rise, instruct them to change the infusion set to rule out malfunction. Teach them to monitor for ketones, to remove the pump, and to use a syringe to inject fast-acting insulin injections when elevated blood glucose levels do not respond to insulin via the pump. Patients need to be advised that even a minor interruption of insulin delivery may result in hyperglycemia or DKA, related to Humalog or Novolog’s fast action.¹⁴

Nurses can reduce the risk of hypoglycemia by continually reinforcing its immediate management. As with all diabetes medication regimens, individuals need to be able to prevent, recognize, and treat low blood sugar. Instruct pump users to treat any blood glucose level of less than 60 mg/dl with 15 to 20 grams of fast-acting carbohydrates, such as a half glass of orange juice, three to four glucose tablets, or glucose gel. After 15 to 20 minutes, they should check blood glucose levels and continue to check them frequently until the target blood glucose level is achieved.

Individuals should be advised to take a bolus after eating, if hypoglycemia occurs before meal times. Individuals who use carbohydrate counting learn that one gram of carbohydrate raises a blood glucose level approximately three to four mg/dl.¹⁵ Knowing the grams of carbohydrates it takes to raise blood glucose levels helps to avoid over treatment of hypoglycemia. If frequent episodes of low blood sugar occur, pump users are advised to evaluate the accuracy of their meal bolus and basal rate.

Participants of the DCCT who chose intensive insulin therapy, whether delivered by MDI or the insulin pump, reported a 10-pound weight gain. Researchers attributed this to the reduction in urine ketones that resulted from improved blood glucose control.¹ If the body does not burn fat for energy, weight loss will not occur. Weight gain was also related to the treatment of hypoglycemia. Some of the additional calories consumed to treat hypoglycemia are stored as fat. Therefore, all pump candidates should consult with an exercise physiologist, who is a certified diabetes educator, to plan an exercise program to prevent weight gain.

Advantages of CSII

The subcutaneous insulin depot — an accumulation of insulin that sometimes occurs at the injection site — causes variability in insulin absorption rate and unpredictable peak levels of NPH or Lente insulin. The amount of insulin that reaches the blood stream for use by cells can vary by 25% from day to day. The basal insulin glargine (Lantus) has a day to day absorption variability of 32%.¹⁶ On the other hand, the insulin absorption rate for insulin pump users may only fluctuate by three percent from day to day.¹⁷ More predictable absorption of insulin and the exclusive use of a constant infusion of fast acting insulin can reduce the risks of hypoglycemia and promote stable blood glucose levels.

The ability to adjust basal rates provides blood glucose level stability. Eighty percent of individuals with type 1 diabetes experience the “Dawn Phenomenon” — a rise in blood glucose levels during the night as a result of accelerated glucose production from the liver.¹⁸ With CSII, the basal rate can be increased to prevent this elevated fasting blood glucose level. Conversely, if pump users experience nocturnal hypoglycemia, the basal rate can be reduced. Studies on pediatric patients have indicated that the need for insulin drops in the early morning hours.¹⁹ This reduction in insulin requirements often leads to hypoglycemia. Often patients are not alerted to this drop in blood glucose overnight. The body’s response to raising the blood glucose level may take place. However, if hypoglycemia continues to occur, individuals with type 1 will eventually lose the ability to recovery from hypoglycemia. This is referred to as “hypoglycemic unawareness.”

The ability to adjust insulin in response to changes in daily routines offers pump users more control over their diabetes. And this control can reduce the incidence of depression, which is prevalent in individuals with diabetes.²⁰

Diabetes is a condition that requires individuals to be responsible for most of their own care. Pump users need to know how to manage all aspects of their own diabetes. When individuals take on this responsibility, they can reduce their risk of complications from retinopathy, neuropathy, nephropathy, and heart disease. Although insulin pump therapy is not a cure for diabetes, it’s an excellent treatment option for motivated individuals. CSII can provide a bright future for those with type 1 and type 2 diabetes who require insulin where the risks are manageable and benefits are many.