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Insulin Pumps

Published:
20-June-2005

By H. Peter Chase MD

An insulin pump is a microcomputer (the size of a pager) that constantly infuses insulin. When an insulin pump is used, insulin is first placed into a special syringe (reservoir), which is placed within the pump case. A small plastic tube (canula) within a needle is put under the skin (the needle is then withdrawn, leaving the plastic tube (canula) in place). Insulin is infused through the canula to an area under the skin. Tape is placed over the canula to keep it in place for up to three days.

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It is important to realize that the current insulin pumps do not know what the blood sugar level is and give 0.1 unit of insulin every few minutes (called the "basal" rate). Each time the person eats, buttons on the pump must be pushed to give an additional "bolus" insulin dose. This is not a "closed-loop" pump that measures blood sugars and turns off the basal insulin if the blood sugar is low or gives more insulin if the blood sugar is high. This will likely become possible at some time in the future.

Advantages of Insulin Pumps

  • Improved Glucose Control - The Diabetes Control and Complications Trial (DCCT) showed that improved lessened the likelihood of eye, kidney, and nerve complications in type 1 diabetes. Glucose control is measured by doing a HbA1c test every three months. Most people who use pump therapy have some decrease in their HbA1c values and thus some decrease in their risk for complications. People who are not able to obtain optimal glucose control on multiple daily injections of insulin may benefit from insulin pump therapy.
  • Insulin Delivery - One if the big advantages of using a pump is that the insulin is readily available; it is relatively easy to push a few buttons to take extra insulin (this could possibly also be an added risk for young children). The insulin pump is designed to deliver insulin in two ways. A programmed basal rate (.01 unit delivered every few minutes) or a user-initiated bolus dose (a quick burst) of insulin with meals or with high blood sugars. This is similar to the insulin output by the normal human pancreas, with a constant (basal) output of insulin and boluses of insulin with meals. The pump has advantages over multiple daily shots in that the absorption of insulin is more consistent and is thus very predictable. Only short acting insulin is used in the pump. Long acting insulins, which vary in their absorption in the same person from day-to-day, are not used in a pump.
  • Reduction or Blood Sugars after Meals or Whenever High - With quick acting insulin, the blood sugars after meals can now be reduced using boluses at mealtime without having to remember to give pump bolus doses 30-90 minutes before eating. In addition, extra doses of insulin are easy to take if a high blood sugar is found between meals. The insulin in the pump works just like when it is given in shots. It starts to work in 10 minutes, peaks in 30-40 minutes, and is gone in four hours.
  • Flexibility and Freedom - For some people, using a pump has psychological advantages. Being able to sleep late in the morning or to alter the times of meals and exercise represents an advantage for many pump users. Basal rates can be easily altered to meet special circumstances. Extra or increased boluses can be taken (e.g., when ill) without having to take extra shots. Many people express an increased sense of freedom and flexibility.

Disadvantages of Insulin Pumps

  • Psychological Factors - Wearing a pump, even though it is not much bigger than a pager, is difficult for some people. A considerable amount of learning about the pump is necessary, and it is not that much different from the amount required when diabetes was first diagnosed. There are other feelings expressed - such as "constantly being hooked to an instrument"
  • Expense - Pumps are expensive and some insurance companies may refuse to pay for them. Initial expenses include buying the pump (around $6000.00), starting the pump or pump classes, and pump supplies. All of these run into the many thousands of dollars. Although this may seem like a lot, the cost savings in the prevention of eye, kidney, and nerve complications of diabetes more than offsets these expenses.
  • Skin Infections - Infections can occur at the infusion sites - particularly if the infusion sets are left in longer than three days. However, if proper cleaning techniques are followed, this is a minimal risk.
  • Hypoglycemia - Severe low blood sugars were three times more common in pump users or in people taking three or more shots per day (all using regular insulin) compared with people receiving one or two shots per day in the DCCT. The use of Novalog with more timely absorption, action, and disappearance has now made pumps safer in relation to hypoglycemia.
  • Weight Gain - People using insulin pumps (resulting in better glucose control) may gain weight as a result. The sugar is absorbed rather than going out in the urine. Working with a dietitian before and after starting the pump can help to prevent this from happening.
  • Ketoacidosis - When problems occur with insulin delivery, there is no long acting insulin in the body. Ketones will start to form in 4-6 hours. There are now warnings on pumps to help indicate a plugged (occluded) line or canula, or the reservoir being out of insulin. In our experience, most pump users have times when their canula comes out or plugs (occludes). Insulin and syringes must be kept available in case they are needed. Urine Keytone strips must also always be available.
  • Insulin Availability - One must remember to routinely fill the insulin reservoir in the pump so that the pump does not run out of insulin at an awkward time.

Methods of Insulin Delivery by Pump

The pump delivers insulin in two ways: 1) a basal dosage that is programmed into the pump and remains the sane day-after-day unless the user changes the rate, and 2) bolus dosages that are taken before meals or when a blood sugar is high, but which must be programmed in by the user at the time the dose is to be taken or it will not be given.

Basal Insulin Dosages - The basal rate reflects the units of insulin per hour that would be needed if a person were not eating meals. The basal rate is similar to the small amount of insulin released by the pancreas every few minutes to turn off sugar production by the liver and to prevent fat breakdown. All people are different, and the use of different basal doses allows for fine-tuning. Once basal rates are set they tend to stay quite consistent, except with large changes in body weight, changes in time zones, injuries, some medications, and temporary reductions for exercise.

Bolus Insulin Dosages - Approximately 40-50% of the daily pump insulin doses are given as boluses before meals or snacks. (Some people give the bolus at the end of the meal when they can better judge amounts eaten.) Everyone is different and boluses can be chosen to fit individual eating habits. However, the first goal is to get the basal doses adjusted, so it is usually suggested to keep the carbohydrate intake relatively consistent for the first two weeks.

Supplemental Insulin Dosages - Extra (unscheduled) insulin boluses are important to use if the blood sugar level is high. It is important to remember that larger dosages will be required if ketones are present. The health care team should be contacted if moderate or large ketones are found.

Insulin pumps have advantages and disadvantages. It is up to each person and family, working with their health care team, to decide if a pump would be good for a given person.

By H. Peter Chase, M.D.
Barbara Davis Center for Childhood Diabetes
Department of Pediatrics