Vol. 13 •Issue 12
• Page 41
Getting Pumped
Continuous Insulin Infusion Therapy
By Caryl D. Sumrall, NP, Kelly K. Land, NP, Fleetwood V. Loustalot III, NP, Ruby Denson, NP, and Marshall J. Bouldin IV, MD
Tight glucose control is an elusive goal, even among highly motivated patients with diabetes. For many people, especially those with type 1 disease, control remains suboptimal despite adherence to traditional regimens such as multiple-dose injection therapy (MDI) or a regimented lifestyle. For these patients, insulin pump therapy may offer an effective solution.
Continuous subcutaneous insulin infusion (CSII) therapy is an established method of achieving tight blood glucose control. CSII delivers rapid-acting insulin subcutaneously via an external insulin pump device. The method is designed to mimic the normal physiologic pattern of endogenous insulin secretion (see figure).
The pump delivers a continuous infusion of rapid-acting insulin each hour at a preprogrammed rate (the basal rate) to supply the body's baseline continuous insulin needs. The patient programs mealtime boluses of insulin to cover anticipated glucose rises, in a pattern analogous to the response of a normal pancreas. These mealtime boluses are typically adjusted according to the nature and amount of food consumed, using standardized methods customized to the patient. The patient can administer additional calculated insulin boluses to correct unexpected hyperglycemia before the meal, along with the mealtime bolus dose.
Although CSII requires a high degree of personal responsibility on the part of the patient, the result can be quite liberating and is often accompanied by satisfaction.1
Background
The first insulin pump was developed about 25 years ago. Since then, manufacturers have made insulin pumps much smaller and more convenient. Insulin pumps are now about the size of a small pager and can be attached to the waistband of a belt, carried in a pocket or held with a strap around the arm. More than 200,000 diabetes patients worldwide are using insulin pumps for daily diabetes management.2 Discontinuation rates for CSII are low and most often related to recurrent irritation of or infection at the infusion site.1
Six manufacturers now sell insulin pumps in the United States: Medtronic MiniMed sells the Paradigm pump, Disetronic sells the Accu-Chek Spirit, Animas Corp. sells the IR1250, Deltec Inc. sells the Cozmo, Sooil Corp. sells the Dana Diabecare II, and Nipro sells the Amigo.
Candidates for CSII
Proper patient selection is critical to safe and successful insulin pump therapy. The American Diabetes Association (ADA) has developed comprehensive criteria for selection.3 The ADA recommends CSII only for patients who are "strongly motivated."3 In addition, patients must have thorough comprehension of the insulin pump and the ability to self-monitor blood glucose levels at least four to six times daily. A sound understanding of carbohydrate counting is essential prior to initiating CSII, to calculate accurate mealtime boluses.
CSII provides greater flexibility than traditional treatments for meal schedules, travel and exercise, and may be considered over MDI in patients with special needs in these areas. Patients on CSII have improved glycemic control compared with conventional therapy and MDI.4 Characteristics of potential pump candidates are outlined in Table 1. Although CSII may be used for both types of diabetes mellitus, it is especially useful for type 2.5
The American Association of Diabetes Educators (AADE) has expanded on the ADA recommendations by noting the need to limit CSII to patients with realistic expectations of the therapy, sound coping mechanisms and social support, and the financial ability to pay for CSII.6 CSII therapy requires multiple complex tasks and a high level of autonomy. A comprehensive education about the principles of CSII is necessary. To ascertain appropriate usage and skills, some experts recommend a saline trial prior to insulin administration.7
Pump Cost
The cost of initiating CSII has decreased dramatically since publication of the Diabetes Control and Complications Trial.Initiation of pump therapy costs between $5,000 and $6,000, and the annual maintenance costs are nearly $1,500.8-11 Varying degrees of financial assistance are available from insurance providers.
Physiologic Measures
Specific physiologic measures should be considered when determining candidacy for CSII. Glycemic control achieved through MDI or CSII has proven more effective in the prevention of microvascular complications of type 1 and type 2 diabetes than conventional therapy.12,13
The risk of severe hypoglycemia was once a serious concern.14 However, a recent meta-analysis comparing CSII, MDI and conventional therapy revealed that patients who use CSII may have fewer episodes of hypoglycemia than their MDI counterparts and achieve better glycemic goals than patients on conventional therapy.15
Dawn Phenomenon
The dawn phenomenon is caused by an early morning rise in growth hormone and is a common occurrence in patients with diabetes.16 It is difficult to compensate for the phenomenon in MDI, since it usually requires an insulin injection around 3 o'clock in the morning. The ability of the insulin pump to program multiple basal rates allows for adjustment of the insulin infusion rate to counteract the effects of the dawn phenomenon. The ability to tailor basal infusion rates, even while the patient is sleeping, provides great flexibility in maintaining euglycemia.
Ketoacidosis
Diabetic ketoacidosis (DKA) is a serious risk associated with rapid-acting insulin delivered with CSII, since there is no depot of long-acting insulin in the body in case of insulin infusion interruption. This risk continues to dissuade some providers or patients from choosing CSII, but multiple studies have reinforced the safety of CSII when coupled with adequate education and training.15,17,18 Finally, pregnancy is an appropriate indication for CSII because pump therapy improves glycemic control and lowers the elevated fetal risk of a hyperglycemic environment.10
Who Is Not Appropriate?
Some patients are not appropriate candidates for CSII therapy. Patients with complex psychological or social issues and patients who have not complied with previous treatment regimens may not achieve glycemic goals while on CSII.15 Furthermore, patients who are unwilling to test blood sugars with the required frequency are not appropriate for CSII therapy.
Screening Protocol Needed
Due to the multiple concerns that need to be addressed before initiating CSII therapy, a screening protocol should be used. One published screening protocol reflects the ADA and AADE recommendations.17 The authors used multiple outpatient visits to assess knowledge about CSII and to counsel patients about the rigors of this therapy. Educational screening visits with the diabetes education staff prior to starting CSII provided a net cost avoidance of nearly $1,700 per subject screened, primarily due to the identification of patients likely to discontinue the therapy. Screening protocols should include detailed assessment addressing personal, social, physiologic and cognitive-psychomotor behavior (Table 2). These protocols should be flexible and individualized to meet the needs of the patient, while providing a realistic frame of reference.19
Patient Management
All patients require a sound knowledge base in carbohydrate counting, insulin pump functions, troubleshooting of problems, signs and symptoms of hypoglycemia and hyperglycemia, and appropriate ways to treat both. Patients must be able to change basal rates and calculate mealtime bolus doses and correction boluses as needed. Patients must keep insulin syringes and vials of insulin immediately available in case of pump malfunction, kinks in tubing or other problems that may prevent the receipt of insulin from the pump. Patients must also have glucose tablets and a glucagon injection kit (especially younger patients) to treat hypoglycemia. Careful attention must be paid to the infusion site to prevent infection.
Once a patient begins CSII therapy, careful and consistent monitoring by the patient is necessary for successful glycemic control. Patients should perform finger stick glucose tests (FSGs) at least four times a day and report the results to their diabetes care team every 1 or 2 weeks after initiating pump therapy and at least monthly after the basal rate has been established and settled.20
CSII therapy uses analog insulin in the form of aspart (NovoLog) or lispro (Humalog). Studies have documented a lower incidence of hypoglycemia with rapid-acting analog insulin compared with regular insulin due to its more rapid onset and shorter duration of action. Additionally, analog insulin more closely mimics the normal physiologic response of the pancreas in response to a meal.21
The Basal Rate
About half of a patient's daily insulin requirements are delivered as basal insulin, and the other half as meal-related boluses. When a person initiates CSII therapy, his or her initial basal rate of rapid-acting insulin infusion is calculated by taking the total daily dose (TDD) of insulin from injections and reducing that dose by 25%. That number is then divided by 2, and then again by 24, to get the basal rate per hour. The equation is written this way:
[prepump TDD - (prepump TDD x 0.25)]/2
24
Initial basal rates typically average between 0.7 units/hour and 0.9 units/hour. The initial basal rate typically requires adjustment, so a follow-up visit within a week is necessary to determine how blood sugars have responded to the initial rate.22
In addition to the initial basal rate, the initial bolus dose of insulin per meal must be determined to counteract postprandial hyperglycemia. To determine the number empirically, calculate the initial mealtime bolus dose from the total daily dose of basal insulin, with the bolus dose being the total daily dose divided by three. This provides the patient with the amount of insulin to bolus per meal, assuming equal carbohydrate servings for three meals. The equation looks like this:
[prepump TDD - (prepump TDD x 0.25)]/2
3
Ideally, the patient should calculate each mealtime bolus based on his or her counting of the carbohydrate grams in that meal and his or her own predetermined carbohydrate-to-insulin ratio. The carbohydrate-to-insulin ratio depends on the patient's degree of insulin resistance and can be determined empirically from the total daily dose of basal insulin: If the basal rate is <0.8 units/hour, one unit per 15 grams of carbohydrates is used initially. If the basal rate is >0.8 units/hour, one unit per 10 grams of carbohydrates is used initially. The bolus dose may also be adjusted based on FSG results before and after meals once patients have started CSII therapy.23
Patients on CSII therapy may also use the insulin pump to correct premeal high blood sugars using the "1800 rule" or insulin sensitivity factor instead of the traditional sliding scale. In the past, patients have been advised to take 1 unit of supplemental insulin for each 30 mg/dL elevation above the target blood sugar level. However, this sliding scale typically applied to people of average size and did not work as well for very small or obese patients. The 1800 rule was developed to help individualize estimates of insulin required to correct hyperglycemia for insulin pump patients of all sizes. The insulin sensitivity factor is 1800 divided by the current total daily insulin dose. Patients then calculate their hyperglycemia correction dose by subtracting their goal blood sugar from their actual blood sugar and dividing this ratio by their own insulin sensitivity factor: (actual FSG — goal FSG)/sensitivity factor = correction dose. The correction bolus is given before meals only, to prevent iatrogenic hypoglycemia. It is given in addition to the premeal bolus.1
Once a basal rate has been established, it is important to test this rate by having the patient skip meals to test for hypoglycemia or hyperglycemia on that particular basal rate. The patient should start by skipping breakfast for 3 days and testing his or her blood sugars each morning before breakfast and before lunch. The basal rate is correctly set if the blood sugar remains the same. Subsequently, a patient may skip lunch for 3 days, testing blood sugars before lunch and before supper. Again, the basal rate is set correctly if the blood sugar remains essentially unchanged.
The same testing pattern may then be used to test the sufficiency of the basal rate from supper to bedtime. This method helps identify problems with the basal rate and determine whether to lower or raise it based on hyperglycemia or hypoglycemia at the meal following the one skipped. Checking blood glucose approximately 2 hours after eating a meal assesses the carbohydrate ratios. If hyperglycemia or hypoglycemia is identified, changing the carbohydrate ratio can alleviate these problems.21,22
Exercise, Illness
Patients on insulin pumps face specific challenges with issues such as exercise and illness. CSII therapy provides flexibility for patients to adjust their basal rate according to food intake and symptoms during illness. Basal rates and bolus doses may also be increased to accommodate increased insulin requirements that can occur with illness. In patients with regular or vigorous exercise regimens, basal rates and boluses may need to be temporarily decreased by 20% to 40% to avoid hypoglycemia. Other activities that may cause hypoglycemia include shopping, housework and yard work. Patients may require additional carbohydrates before these activities.1
Skin Infection
The No. 1 cause of pump discontinuation is skin infections at the infusion site. Infections can range from small areas of mild inflammation to abscesses that have to be surgically incised and drained. To reduce the risk of infection, advise patients to keep the infusion set and the area of injection clean and dry. Changing the infusion set every 24 to 72 hours also helps.1
Hyperglycemia
Patients on insulin pumps may experience unexplained hyperglycemia and ketoacidosis. If illness is not the cause, determine whether increased dietary intake, increased stress or activity levels, or disruption in insulin delivery may be to blame. If elevated blood glucose persists despite additional boluses, patients should do a detailed check of the pump, the infusion set and site, the insulin cartridge and syringe, and the insulin itself. Causes of unexplained hyperglycemia related to disruption of insulin delivery include partial or complete occlusion of the infusion set, pump malfunction, and poor absorption due to scar tissue at the infusion site. Patients should have extra insulin and syringes to use for MDI in case of pump malfunction. Troubleshooting may also be provided by the pump manufacturer and the diabetes care team.1
Continuous Wear
The insulin pump should be worn at all times. Patients often fear that the pump will interfere with activities they enjoy, such as swimming or sex. Pumps may be removed for no more than 1 or 2 hours. For swimming or showering, the patient can place the pump in a waterproof holder. Some pumps are watertight. Options during sexual activity or sleeping include using infusion sites with longer tubing, placing the pump on the bed or under pillows, or, for women, securing it in a garter. Patients should check FSG levels often after reinstalling the pump, to ensure that it is working properly.1
Complications
Problems may arise when patients on CSII therapy seek emergency care for blood glucose abnormalities. The average health care provider is not trained in CSII therapy and may not know how to effectively manage blood glucose abnormalities that occur while on the pump. In many cases, emergency department personnel disconnect the pump, albeit temporarily, and manage the patient's blood sugar abnormalities with traditional insulin injections.
While this is an acceptable and often necessary choice, patients in this situation have no long-acting insulin in their bodies and are therefore at high risk of DKA, especially if only covered by analog or regular insulin. Because the patient is only receiving rapid-acting insulin through the pump, he or she can develop DKA quickly due to the absence of any long-acting basal insulin. The lispro or aspart will be metabolized in 1 or 2 hours.
Communication with the patient's diabetes management team can help resolve confusion and prevent unnecessary discontinuation of pump therapy. Thorough instruction about appropriate sick day management may reduce emergency department visits. In general, if pump and insulin delivery have been evaluated and are not in question, it is usually best to leave the pump in place and continue CSII.
Patients on insulin pump therapy also have an increased risk of hypoglycemia, and it is often severe. Frequent FSG monitoring (at least four to six times a day) helps identify and treat hypoglycemic episodes, especially if the patient has a history of hypoglycemia unawareness. In patients on an insulin pump, hypoglycemia often results from inappropriate timing of insulin in relation to meal consumption or from overbolusing for the amount of food to be consumed. In addition, patients may experience hypoglycemia if they consume inadequate calories to supplement vigorous activity. Frequent monitoring of blood glucoses and adjustment of carbohydrate-to-insulin ratios may help prevent hypoglycemia. Consistently review appropriate treatment of hypoglycemia with each patient.1
Paying for the Pump and Supplies
Medicare has strict reimbursement guidelines for insulin pump therapy. Initially, the patient must have a fasting C-peptide of ²110% of the lower limit of normal. In addition, one of the two following criteria must be met:23
• "The patient has completed a comprehensive diabetes education program, has been on a program of multiple daily injections of insulin (i.e., at least three injections per day), with frequent self-adjustments of insulin dose for at least 6 months prior to initiation of the insulin pump, and has documented frequency of glucose self-monitoring an average of at least four times per day during the 2 months prior to initiation of the pump, and meets one or more of the following criteria while on the multiple injection regimen: glycosylated hemoglobin level greater than 7%; history of recurring hypoglycemia; wide fluctuations in blood glucose before meals; dawn phenomenon with fasting blood glucose frequently exceeding 200 mg/dL; and history of severe glycemic excursions.
• "The patient has been on an external insulin infusion pump prior to enrollment in Medicare and has documented frequency of glucose self-testing an average of at least four times per day during the month prior to Medicare enrollment."
Medicaid guidelines for reimbursement are just as stringent as the Medicare guidelines, but can be even more confusing since they vary from state to state.
For patients with private insurance, it is imperative that the patient and the diabetes care team members determine whether the plan provides reimbursement for this expensive treatment.
Future of CSII
The future of CSII therapy is directed toward implantable insulin pumps and continuous glucose sensors with the ultimate goal of a combining the two.
Continuous glucose sensors can be worn in the same manner as the pump. The sensor is placed subcutaneously in the abdomen and is changed every 3 days, much like the infusion set on an insulin pump. These continuous glucose sensors provide 200 to 400 blood sugar readings per day and can provide a more accurate picture of the patient's blood sugar variations, identifying unrecognized problems so that changes in medication therapy can be made. Continuous glucose sensors may be especially helpful for children, who may be more likely to have fluctuating blood sugars due to erratic food intake and activity levels. Continuous glucose sensors have proven useful in detecting asymptomatic hypoglycemia.1
Implantable insulin pumps are surgically implanted in the abdomen and deliver bursts of insulin every few seconds in much the same way the pancreas does. The first implantable pump, manufactured by Medtronic MiniMed, has a reservoir that must be refilled with insulin by injection every 2 or 3 months. The implantable insulin pump is available in Europe but is in the investigational stage in the United States.
Of course, the ultimate goal is the development of a closed-loop artificial implantable pancreas with an external or implantable glucose sensor that will feed back to the pump, rendering finger stick testing and insulin injections obsolete and liberating patients from many of the continuous concerns of CSII and MDI.24
For now, however, CSII therapy offers an excellent option for diabetes patients who need tighter control of their glucose levels and desire more flexibility.
References
1. Insulin infusion pump therapy. In: Klingensmith GJ, ed. Intensive Diabetes Management. Alexandria, Va.: American Diabetes Association; 2003:99-120.
2. DeVries JH, et al. A randomized trial of continuous subcutaneous insulin infusion and intensive injection therapy in type 1 diabetes for patients with long-standing poor glycemic control. Diabetes Care. 2002;25:2074-2080.
3. American Diabetes Association. Clinical practice recommendations 2003. Diabetes Care. 2003;26:33S-50S.
4. Weissberg-Benchell J, Antisdel-Lomaglio J, Seshadri R. Insulin pump therapy: a meta-analysis. Diabetes Care. 2003;26(4):1079-1087.
5. Tanenberg RJ. Candidate selection. In: Fredrickson L, ed. The Insulin Pump Therapy Book: Insights from the Experts. Los Angeles, Calif.: Minimed Inc; 1995:20-30.
6. American Association of Diabetes Educators. Position statement: education for continuous subcutaneous insulin infusion pump users. The Diabetes Educator. 2003;29:97-99.
7. Sanfield J, Hegstad M, Hanna R. Protocol for outpatient screening and initiation of subcutaneous insulin infusion therapy: impact on cost and quality. The Diabetes Educator. 2002;28:599-607.
8. Herman W, et al. Assessing the impact of intensive insulin therapy on the health care system. Diabetes Review. 1994;2:384-388.
9. Diabetes Control and Complications Trial Research Group. Resources utilization and costs of care in the Diabetes Control and Complications Trial. Diabetes Care. 1995;18:1468-1478.
10. Lenhard J, Reeves G. Continuous subcutaneous insulin infusion: a comprehensive review of insulin pump therapy. Arch Intern Med. 2001;161:2293-2300.
11. Herman W, Dasbach E, Songer T, Eastman R. The cost-effectiveness of intensive therapy for diabetes mellitus. Endocrinol Meta Clin North Am. 1997;26:679-695.
12. Diabetes Control and Complications Trial Research Group. The effect of intensive treatment of diabetes on the development and progression of long-term complications of long-term complications in insulin-dependent diabetes mellitus. N Engl J Med. 1993;329:977-985.
13. UK Prospective Diabetes Study (UKPDS) Group. Intensive blood glucose control with sulfonylureas or insulin compared with conventional treatment and risk of complications in patients with type 2 diabetes (UKPDS33). Lancet. 1998;352:837-853.
14. Locke D, Rigg L. Hypoglycemic coma associated with subcutaneous insulin infusion by portable pump. Diabetes Care. 1981;4:389-391.
15. Pickup J, Keen H. Continuous subcutaneous insulin infusion at 25 years: evidence base for the expanding use of insulin pump therapy in type 1 diabetes. Diabetes Care. 2002;25:593-598.
16. Campbell P, et al. Pathogenesis of the dawn phenomena in patients with insulin dependent diabetes mellitus. N Engl J Med. 1985;312:1473-1479.
17. Boland E, et al. Continuous subcutaneous insulin infusion: a new way to lower risk of severe hypoglycemia, improve metabolic control, and enhance coping in adolescents with type 1 diabetes. Diabetes Care. 1999;22:1779-1784.
18. Bending J, Pickup J, Keen H. Frequency of diabetic ketoacidosis and hypoglycemic coma during treatment with continuous subcutaneous insulin infusion. Am J Med. 1985;79:685-691.
19. Bode BW, Davidson PC. Pattern analysis and recordkeeping. In: Fredrickson L, ed. The Insulin Pump Therapy Book; Insights from the Experts. Los Angeles, Calif.: Minimed Inc.; 1995:84-93.
20. Homko C, et al. Comparison of aspart and lispro. Diabetes Care. 2003;26:2027-2031.
21. Bode BW. Establishing and verifying basal Rates. In: Fredrickson L, ed. The Insulin Pump Therapy Book; Insights from the Experts. Los Angeles, Calif.: Minimed Inc; 1995:48-56.
22. Davidson PC. Bolus and supplemental insulin. In: Fredrickson L, ed. The Insulin Pump Therapy Book; Insights from the Experts. Los Angeles, Calif.: Minimed Inc; 1995:58-71.
23. Centers for Medicare Services. Medicare coverage of insulin pumps. Available at: http://www.cms.hhs.gov/manuals/pm_trans/R143CIM.pdf. Accessed Sept. 7, 2005.
24. Medtronic MiniMed. The Medtronic MiniMed 2007 Implantable Insulin Pump System. Available at: http://www.minimed.com/professionals/products/implantablepump/eu.html. Accessed Sept. 7, 2005.
Caryl Sumrall is a family nurse practitioner at University of Mississippi Medical Center in Jackson, Miss. Kelly Land is a family nurse practitioner at the Jackson Medical Mall Diabetes Clinic in Jackson. Fleetwood Loustalot is a family nurse practitioner at the Jackson Medical Mall Diabetes Clinic. Ruby Denson is a family nurse practitioner at G.V. "Sonny" Montgomery Veterans Affairs Medical Center in Jackson. Marshall Bouldin is a medical doctor who practices in the Division of General Medicine at University of Mississippi Medical Center.
Table 1: Events or Characteristics That Warrant Pump Consideration
• History of hypoglycemia unawareness
• Pregnancy or plans to become pregnant
• Childhood or adolescence
• Flexibility at work
• Need for improved glycemic control
• History of dawn phenomenon
• History of poor glycemic control with hemoglobin A1C >7%
• History of widely fluctuating blood sugars
Table 2: Factors to Consider Before Initiating Insulin Pump Therapy
• Self-motivation
• Willingness to do daily finger sticks
• Age
• Ability to recognize hypoglycemia
• Finances
• Other medical conditions
• Type of diabetes
• Ability to problem-solve
• Lifestyle and occupation
• Psychosocial criteria
• Complications from disease
• Ability to comprehend CSII therapy
• Familial and other support
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