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DEFINITION

• Insulin pumps (technically called Continuous Subcutaneous Insulin Infusion, CSII) deliver insulin at programmed rates, from a pump worn externally through a small catheter tip inserted into the skin. Most current brands worn on a belt, with a catheter and insertion site that is changed about every three days; one brand is worn directly on the skin and discarded after three days.
• May be linked to a glucose monitor, displaying real-time blood glucose results, but insulin delivery is not driven by the blood glucose result; fully closed loop delivery system does not currently exist. Insulin delivery rates and amounts are determined by the patient.
• CSII is an option for treating type 1 diabetes or unstable, insulin-requiring type 2 diabetes.
• Only use rapid-acting (e.g. aspart, lispro or glulisine) or regular insulin.

EPIDEMIOLOGY

• Available since the 1980's, over 400,000 insulin pumps sold per year.
• Use varies widely from country to country: in the USA, up to 20% of people with type 1 diabetes use a pump; in many other countries less than 1% do.
• Reports are inconsistent about whether CSII improves glycemic control, although severe hypoglycemia seems to be less frequent (Pickup).
• Incidence of ketoacidosis more common with CSII because if delivery stops, insulin delivery also immediately stops (Hanas).
• CSII is not reimbursed by Medicare in the U.S. for people with type 2 diabetes. Medicare requires that a c-peptide assay show lack of endogenous insulin production.

CLINICAL TREATMENT

• Patient selection is essential: best success if patient understands their diabetes well, self-monitors blood glucose multiple times daily, counts carbohydrates, is not well controlled or subject to severe hypoglycemia on multiple dose insulin regimens, has a variable and demanding life style, is comfortable with technology, and wants to use the pump.
• Prior to choosing pump therapy, a diabetes educator should review carbohydrate counting, and demonstrate pump use to potential patient.
• Insulin delivery is divided into basal rates and bolus doses. Calculate starting doses based on previous total daily insulin requirements.
• Basal rate, programmed to deliver a sequence of pre-programmed hourly rates which repeat every 24 hours, should deliver about half the total daily dose. Example: If total daily dose (TDD) was 48 units/day, basal rate will deliver about 24 U/day, or 1.0 U/hour; bolus doses will deliver about 24 U/day total. Be conservative: start with total basal rate about 80% of patient's dose of long-acting insulin.
• Generally 2-4 different basal rates are optimal. Example: Rate 1 starting at midnight; Rate 2 increased about 30-50% at dawn hours; Rate 3 during the day; and Rate 4 may be different in the evenings.
• Bolus doses are chosen and delivered shortly before a meal is ingested, and sometimes to correct high glucose between meals.
• Typical bolus doses are: 1) "nutritional" plus 2) "correctional". Nutritional is based on carbohydrate content of the meal to be ingested (example: 1 unit insulin per 15 grams carbohydrate). Correctional dose designed to bring glucose back to a target level (example: 1 unit per 30 mg/dl above a target glucose level of 120 mg/dl). These doses are only illustrations, individualize doses to each patient.
• To estimate carbohydrate ratio for patient who was not previously carbohydrate counting, use "450" (or 500) rule: 450/TDD = grams of carbohydrate covered by 1 unit of insulin. Individualize for each patient based on history. Example: if TDD 45, 450/45 = 10. Bolus 1 U per 10 g carb.
• To estimate correctional bolus, use "1800" rule for rapid-acting insulin (or 1500 for regular insulin): 1800/total daily insulin dose = mg/dl that 1 unit of insulin will lower blood glucose. Individualize for each patient based on history. Example: if TDD 45, 1800/45 = 40. Bolus 1 U per 40 mg/dl glucose above target glucose level.
• Review emergency procedures, particularly for when pump insulin delivery is interrupted for any reason (i.e. catheter malfunction), including restarting multiple dose insulin injections; patient should have long-acting insulin available if needed for emergencies.

• Bolus dose calculator: Different pumps call this by different names, but it calculates amount of bolus insulin needed using pre-programmed carbohydrate ratios, insulin sensitivity factors, and target glucose levels. Patient enters grams of carbohydrate to be consumed and pre-meal blood glucose level. Insulin on board subtracted from calculated bolus dose. Pump suggests dose but patient still needs to implement dose.
• Insulin on board: prevents overcompensating with bolus insulin by calculating time from last bolus and, based on duration of insulin effect, amount of insulin still "on board". This can be subtracted from insulin dose needed for current meal to obtain amount of additional bolus insulin to inject.
• Square wave bolus: slow infusion of insulin over time as opposed to standard bolus which delivers "spike" of insulin. May be appropriate to cover high fat or protein meals, or in patients with slower digestion (e.g. gastroparesis).
• Daily totals: calculates total bolus and basal insulin dosage delivered per day.
• Temporary basal rates: programmed and activated by patient in situations where insulin needs may be higher or lower than usual (e.g. physical activity, illness, or menses).

FOLLOW UP

• Must have knowledgeable health care professionals available, with close patient contact when initiating insulin pump therapy.
• Common follow-up issues include emergency management of discontinued insulin delivery, sick days, unusual exercise, tape allergies, and frequency of changing the insertion set.
• Some patients take "pump vacations" (e.g. for cosmetic reasons), returning to conventional insulin injections for short periods of time, although such intermittent use is not recommended.
• Discuss what to do during exercise (e.g. take pump off if <30 minutes of activity, reduce basal rate, and/or take snack beforehand).

EXPERT COMMENTS

• Patients must be willing and eager to use a pump; do not force a pump on an unwilling patient.
• Patients need to know that the pump is "open loop", not delivering insulin automatically but requiring input from the patient.
• Discourage unrealistic expectations; pumps may confer significant benefits, but require patients to be involved.
• Many people find insulin pump use valuable in controlling wide glucose fluctuations and more flexible than multiple daily insulin injections. Often improves both quality of life and A1c for many patients.
• Disadvantages of pump therapy include need to be attached to pump at all times and expense. Be sure of insurance coverage before ordering a pump.
• Too many basal rates (for instance 6-10 per day) are not valuable, and suggest that the patient is using different basal rates to cover meals, rather than choosing the correct bolus dose for a meal.
• Giving bolus doses after eating a meal is not recommended.
• Also, frequently giving correctional doses between meals is not recommended, and suggests that the pre-meal bolus dose is too little.
• In general, bolus doses at bedtime are not recommended, but if given to cover a snack, consider more conservative dosing.
• Do not count on an insulin pump to correct poor glycemic control due to poor self-care, or to reverse established long-term diabetic complications.

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