insulin pump

Insulin pump attached to its user with an infusion set.

Insulin pump, showing an infusion set loaded into spring-loaded insertion device. A reservoir is attached to the infusion set (shown here removed from the pump).

Filling an insulin pump reservoir. (Right to left) 1: Reservoir in sterile packaging. 2: Filling the reservoir. 3: Reservoir with needle and plunger removed, ready for attachment to infusion set.

Customizing the basal rate pattern (units per hour) on an insulin pump

An insulin pump is a medical device used for administering insulin in the treatment of diabetes mellitus, also known as continuous subcutaneous insulin infusion therapy. The device includes:

• the pump itself (including controls, processing module, and batteries)
• a disposable reservoir for insulin (inside the pump)
• a disposable infusion set, including a cannula for subcutaneuos insertion (under the skin) and a tubing system to interface the insulin reservoir to the cannula.

An insulin pump is an alternative to multiple daily injections of insulin by insulin syringe or an insulin pen and allows for intensive insulin therapy when used in conjunction with blood glucose monitoring and carb counting.

Setting up

In order to use an insulin pump, the reservoir must first be filled with insulin. Some pumps are designed to be used with prefilled cartridges that are replaced when empty. Most, however, must be filled with insulin of the user's choice (usually Novolog, Humalog, or Apidra). Setting up includes:

1. Opening a new (sterile) empty pump reservoir of the manufacturer's design;
2. Withdrawing the plunger;
3. Inserting the needle into a vial of insulin;
4. Injecting the air from the reservoir into the vial to prevent a vacuum forming in the vial as insulin is withdrawn;
5. Drawing insulin into the reservoir with the plunger, and then removing the needle;
6. Squirting out any air bubbles from the reservoir, and then removing the plunger;
7. Attaching the reservoir to the infusion set tubing;
8. Installing the assembly into the pump and priming the tubing (pushing insulin and any air bubbles through the tubing) - it is essential that this is done with the pump disconnected from the body to prevent accidental insulin delivery;
9. Attaching to the infusion "site" (and priming the cannula if a new set has been inserted).

Dosing

An insulin pump allows the replacement of slow-acting insulin for basal needs with a continuous infusion of rapid-acting insulin.

The insulin pump delivers a single type of fast-acting insulin in two ways:

• a bolus dose that is pumped to cover food eaten or to correct a high blood glucose level.
• a basal dose that is pumped continuously at an adjustable basal rate to deliver insulin needed between meals and at night.

Bolus Shaping

An insulin pump user has the ability to influence the profile of the rapid-acting insulin by shaping the bolus. While each user must experiment with bolus shapes to determine what is best for any given food, they can improve control of blood sugar by adapting the bolus shape to their needs.

A standard bolus is an infusion of insulin pumped completely at the onset of the bolus. It is most similar to an injection. By pumping with a "spike" shape, the expected action is the fastest possible bolus for that type of insulin. The standard bolus is most appropriate when eating high carb low protein low fat meals because it will return blood sugar to normal levels quickly.

An extended bolus is a slow infusion of insulin spread out over time. By pumping with a "square wave" shape, the bolus avoids a high initial dose of insulin that may enter the blood and cause low blood sugar before digestion can facilitate sugar entering the blood. The extended bolus also extends the action of insulin well beyond that of the insulin alone. The extended bolus is appropriate when covering high fat high protein meals such as steak, which will be raising blood sugar for many hours past the onset of the bolus. The extended bolus is also useful for those with slow digestion (such as with gastroparesis or Coeliac disease).

A combination bolus is the combination of a standard bolus spike with an extended bolus square wave. This shape provides a large dose of insulin up front, and then also extends the tail of the insulin action. The combination bolus is appropriate for high carb high fat meals such as pizza, pasta with heavy cream sauce, and chocolate cake.

A super bolus is a method of increasing the spike of the standard bolus. Since the action of the bolus insulin in the blood stream will extend for several hours, the basal insulin could be stopped or reduced during this time. This facilitates the "borrowing" of the basal insulin and including it into the bolus spike to deliver the same total insulin with faster action than can be achieved with spike and basal rate together. The super bolus is useful for certain foods (like sugary breakfast cereals) which cause a large post-prandial peak of blood sugar. It attacks the blood sugar peak with the fastest delivery of insulin that can be practically achieved by pumping.

Bolus Timing

Since the pump user is responsible to manually start a bolus, this provides an opportunity for the user to pre-bolus to improve upon the insulin pump's capability to prevent post-prandial hypoglycemia. A pre-bolus is simply a bolus of insulin given before it is actually needed to cover carbohydrates eaten.

There are two situations where a pre-bolus is helpful:

1. A pre-bolus of insulin will mitigate a spike in blood sugar that results from eating high glycemic foods. Infused insulin analogs such as NovoLog and Humalog typically begin to impact blood sugar levels 15 or 20 minutes after infusion. As a result, easily digested sugars often hit the bloodstream much faster than infused insulin intended to cover them, and the blood sugar level spikes upward as a result. If the bolus were to be infused 20 minutes before eating, then the pre-bolused insulin will be hitting the bloodstream simultaneously with the digested sugars to control the magnitude of the spike.
2. A pre-bolus of insulin can also combine a meal bolus and a correction bolus when the blood sugar is above the target range before a meal. The timing of the bolus is a controllable variable to bring down the blood sugar level before eating again causes it to increase.

Both the blood sugar level as well as the type of food eaten has an impact on the ideal time to pre-bolus with the pump. New insulin analogs are "fast" enough to be given right before a meal, but this is ideal only when starting with a blood glucose value that is within range and the food to be eaten is of moderate glycemic index. If a time period of 15 or 20 minutes is considered to be a "time increment," then the pre-bolus time can be estimated by multiple increments. The time period is increased by one increment when blood glucose in high or when glycemic index is high. Time increments can also double, cancel, or go negative as the situation calls for as shown in the table below. Note however that an extended bolus allowed from the newer insulin pumps may be more convenient than a delayed standard bolus for a situation with low BG and low glycemic food to slow down the action of insulin.

Basal Rate Patterns

The pattern for delivering basal insulin throughout the day can also be customized with a pattern to suit the pump user.

• A reduction of basal at night to prevent low blood sugar in infants and toddlers.
• An increase of basal at night to counteract high blood sugar levels due to growth hormone in teenagers.
• A pre-dawn increase to prevent high blood sugar due to the dawn effect in adults and teens.
• In a proactive plan before regularly scheduled exercise times such as morning gym for elementary school children or after school basketball practice for high school children.

Basal Rate Determination

Basal insulin requirements will vary between individuals and periods of the day. The basal rate for a particular time period is determined by fasting while periodically evaluating the blood sugar level. Neither food nor bolus insulin must be taken for 4 hours prior to or during the evaluation period. If the blood sugar level changes dramatically during evaluation, then the basal rate can be adjusted to increase or decrease insulin delivery to keep the blood sugar level approximately steady.

For instance, to determine an individual's morning basal requirement, they must skip breakfast. On waking, they would test their blood glucose level periodically until lunch. Changes in blood glucose level are compensated with adjustments in the morning basal rate. The process is repeated over several days, varying the fasting period, until a 24-hour basal profile has been built up which keeps fasting blood sugar levels relatively steady. Once the basal rate is matched to the fasting basal insulin need, the pump user will then gain the flexibility to skip or postpone meals such as sleeping late on the weekends or working overtime on a weekday.

Many factors can change insulin requirements and require an adjustment to the basal rate:

• continued beta cell death following diagnosis of type 1 diabetes (honeymoon period)
• growth spurts particularly during puberty
• weight gain or loss
• any drug treatment that affects insulin sensitivity (e.g. corticosteroids)
• eating, sleeping, or exercise routine changes
• whenever the control over hyperglycemia is degrading
• and according to the seasons.

A pump user should be educated by their diabetes care professional about basal rate determination before beginning pump therapy.

Temporary Basal Rates

Since the basal insulin is provided as a rapid-acting insulin, the basal insulin can be immediately increased or decreased as needed with a temporary basal rate. Examples when this is helpful include:

• During a long car drive, when more insulin is needed due to inactivity.
• During and after spontaneous exercise or sports activities, when the body needs less insulin.
• During illness or stress, when basal demand increases due to insulin resistance.
• When blood ketones are present, when additional insulin is needed.
• During menses, when additional basal insulin is needed.

Advantages of pumping insulin

• The use of rapid-acting insulin for basal needs offers relative freedom from a structured meal and exercise regimen previously needed to control blood sugar with slow-acting insulin.
• Many pumpers feel that bolusing insulin from a pump is more convenient and discreet than injection.
• Insulin pumps also make it possible to deliver more precise amounts of insulin than can be injected using a syringe. This supports tighter control over blood sugar and Hemoglobin A1c levels, reducing the chance of long-term complications associated with diabetes. This is predicted to result in a long term cost savings relative to multiple daily injections.[1]

Disadvantages of pumping insulin

• Insulin pumps, cartridges, and infusion sets are more expensive than syringes used for insulin injection.
• Since the insulin pump needs to be worn most of the time, pump users need strategies to participate in activities that may damage the pump, such as rough sports and activities in the water. Some users may find that wearing the pump all the time (together with the infusion set tubing) is uncomfortable or unwieldy.
• An episode of diabetic ketoacidosis may occur if the pump user does not receive sufficient fast acting insulin for many hours. This can happen if the pump battery is discharged, if the insulin resevoir runs empty, the tubing becomes loose and insulin leaks rather than being injected, or if the cannula becomes bent or kinked in the body, preventing delivery. Therefore pump users typically monitor their blood sugars more frequently to evaluate the effectiveness of insulin delivery.

Acceptability

Use of insulin pumps is increasing throughout the world because:

• it provides an easier means to deliver multiple insulin injections for those using intensive insulin therapy. This is especially true for children and others who are uncomfortable with needles (although the pump user still has to inject an infusion set every few days, and poke fingers for blood glucose tests many times a day).
• acceptance among doctors and insurance companies due to the benefits contributing to reducing the incidence of long-term complications. It's also interesting to note that because of differences in health insurance and public funding, the US has about 150,000 pump users. In the UK, NICE have now ruled that if a Type 1 diabetic patient's doctor agrees that they should be using an insulin pump, they should apply to the NHS and they will fund it, this does not apply to Type 2 diabetes http://www.nice.org.uk/guidance/TA57. Therefore numbers are increasing but are still less than the USA, there are around 1100 pump users in the UK by comparison.
• improvements in blood glucose monitoring. New meters require smaller drops of blood, and the corresponding lancet poke in the fingers is smaller and less painful. These meters also support alternate site testing for the most routine tests for practically painless testing. This compensates for the need for pump users to test blood sugar more frequently.
• techniques learned to adapt their pump use to sports, exercise, and water sports. Expert help is becoming common in user groups and books. The pump can be effectively combined with partial basal insulin from the pump and partial basal insulin from a long-acting insulin such as Lantus and Levemir. This is becoming known as the Untethered Regimen.

Recent developments

New insulin pumps are becoming "smart" as new features are added to their design. These simplify the tasks involved in delivering an insulin bolus.

• insulin on board: Based on the time and quantity of the last bolus, the pump software keeps track of the insulin remaining in the bloodstream and displays it on the screen. This supports the process of performing a new bolus before the effects of the last bolus are complete, and thereby helps prevent the user from overcompensating for high blood sugar with unnecessary correction boluses.
• bolus calculators: Pump software helps by calculating the dose for the next insulin bolus. The user enters the grams of carbohydrates to be consumed, and the bolus "wizard" calculates the number of units of insulin needed. It adjusts for the most recent blood glucose level and the insulin on board, and then suggests the best insulin dose to the user to approve and bolus.
• custom alarms: The pump can monitor for activities during specific times of day and then alarm the user if an expected activity did not occur. Examples include a missed lunch bolus, a missed blood glucose test at 10am, a new blood glucose test 15 minutes after a low blood glucose test, etc. The alarms can be customized to support each user.
• touch bolus: For persons with visual impairments, this button on the pump can be used to bolus for insulin without using the display. This works with a system of beeps to confirm the bolus parameters to the pump user.
• interface to personal computers: New pumps interface to personal computers for managing and documenting pumps delivery programs and to upload data from the pump. This simplifies record keeping and can be interfaced with diabetes management software.
• integration with blood glucose meters: Blood glucose data can be manually entered into the pump for supporting the bolus wizard for calculation of the next insulin bolus. Some pumps are supporting an interface from the insulin pump to a blood glucose meter.
  • The Cozmo pump works with the CozMonitor (using Freestyle test strips) attached to the back of the pump. The pump receives glucose readings from this attached meter via infrared (IR).
  • The Medtronic Diabetes Minimed Paradigm series of insulin pumps allow for radio frequency (RF) communication. This enables the pump to receive data from a BD or Ascentia blood glucose meter. The RF link also supports a continuous blood glucose sensor known as the "Guardian" which provides the blood glucose value every 5 minutes for display right on the pump screen.
  • The Insulet Omnipod has a separate electronic display with a built-in meter that uses Freestyle test strips.
• An RF remote control: allows a discrete bolus when the pump is concealed or inaccessible.
• tubeless pod: The Omnipod pump can be attached directly to the skin by its infusion set, eliminating the tube from the pump.

Current insulin pump manufacturers

• http://www.animascorp.com/
• http://www.medtronicdiabetes.com/
• http://www.disetronic-usa.com/
• http://www.cozmore.com/
• http://www.niprodiabetes.com/home.html
• http://www.myomnipod.com/

Future developments

• When insulin pump technology is combined with a continuous blood glucose monitoring system, the technology seems promising for real-time control of the blood sugar level. Currently there are no mature algorithms to automatically control the insulin delivery based on feedback of the blood glucose level. When the loop is closed, the system may function as an artificial pancreas.
• Insulin pumps are being used for infusing pramlintide (brand name Symlin, or synthetic amylin) with insulin for improved post-prandial glycemic control compared to insulin alone.
• An insulin pump that can be surgically implanted inside the body will be available soon by Medtronic. It is the approximate size of a hockey puck, and communicates via RF to an external control. It is refilled by injection through the skin, and holds approximately 2 weeks of insulin.
• A Wristop may soon function as a remote control for an insulin pump.

Bibliography

• Chapter 6 of "Understanding Diabetes" a.k.a. "The Pink Panther Book" by H. Peter Chase
• Pumping Insulin, by John Walsh and Ruth Roberts
• Smart Pumping, by Howard Wolpert
• Think Like A Pancreas, by Gary Scheiner
• "Strike The Spike! Strategies for Combatting After-Meal Highs:" an instructional presentation by Gary Scheiner

External links

• American Diabetes Association guide to insulin pumps
• A pump users' support group for adults
• A pump users' support group for kids
• National Diabetes Information Clearinghouse

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