Diabetes mellitus affects over 34 million people in the United States, and the number is growing. Of those, a subset is dependent on insulin therapy for blood glucose control, which can delay the onset and slow progression of diabetes-associated complications, including retinopathy, nephropathy, and neuropathy. Currently, there are two regimens for insulin delivery: multiple daily injections or continuous subcutaneous insulin infusion, also known as insulin pump therapy. With technological advances, reduction in costs, and data from randomized clinical trials, a growing population of patients are using continuous subcutaneous insulin infusion. For medical professionals, general knowledge of how the medical device functions and indications for removal of the device can help improve patient care and outcomes.
Continuous subcutaneous insulin infusion therapy consists of a pump and infusion set. For the majority of devices, the pump and infusion set are separate, connected by thin plastic tubing, but some devices combine both into one. The infusion set is attached to the patient with a cannula placed in the subcutaneous tissue and secured with adhesive. Infusion sets are typically placed into the upper arm, abdomen, lower back, and upper thigh and changed every two to three days. The pump contains the reservoir and battery. The reservoir typically holds a two to a three-day supply of rapid-acting insulin analog with insulin lispro being the most common. It requires replacement after using up the insulin. Battery requirements vary from device to device; some contain a lithium battery that is rechargeable using a cable, whereas others require a standard alkaline battery. Pumps should merit consideration to be always on if there is a functioning battery. Often the pump will be in standby mode to conserve battery. Returning to an active home screen requires a specific series of button presses that vary depending on the device. From the home screen, there will be options to review basal insulin settings and the history of delivered insulin boluses. Additionally, there will be settings for priming the device for changing infusion sets and insulin reservoirs. Pumps are designed to mimic the natural insulin delivery of the pancreas by continuously delivering short-acting insulin at a basal rate required for maintaining control of blood glucose when fasting. This rate can be set on an hourly basis allowing for tighter control of blood sugars throughout the day. During meals, the pump is programmable to deliver an insulin bolus basal on the macronutrient composition. With insulin pumps, there is the option for different bolus profiles, including dual wave, short extended, and long extended, that is beyond the scope of this article. In summary, the two significant differences between multiple daily injections and continuous subcutaneous insulin infusion are the replacement of long-acting insulin with a continuous basal rate of short-acting insulin and the ability to have varied bolus profiles with meals, with the goal of more closely mimicking the pancreas' native function.
Hyperglycemia: Insulin lispro and its analogs are rapid-acting with the onset of action within 15 minutes, peaking in approximately 60 minutes and lasting less than five hours after injection. In patients on a continuous subcutaneous insulin infusion, hyperglycemia secondary to disruption in insulin delivery must be on the differential. The clinician should always check the infusion site during the physical exam. The easiest way to evaluate is to deliver an insulin bolus via the pump and recheck blood glucose. If blood glucose remains elevated despite insulin bolus, the tubing or infusion set is likely compromised and requires replacement. If the patient is unable to replace the unit, then consider restarting multiple daily injections with long and short-acting insulins. The daily requirement of long-acting insulin can be calculated from the patient's basal rate.
Infusion site infection, erythema, induration, tenderness to palpation, or signs of fluid leakage from the infusion site are all indications for removal, and a new site should be chosen at a different location.
Diabetic ketoacidosis. Since insulin lispro remains active for a relatively short duration, the risk for diabetic ketoacidosis is a concern. Studies comparing incidence in patients treated with continuous subcutaneous insulin infusion versus multiple daily injections have actually demonstrated lower rates of diabetic ketoacidosis in patients on a continuous subcutaneous insulin infusion.
Hypoglycemia: The use of continuous subcutaneous insulin infusion is associated with lower hemoglobin A1c levels, and so there are concerns for increased risk of hypoglycemia. Studies have shown that event rates of severe hypoglycemia and hypoglycemic coma was significantly lower with continuous subcutaneous insulin infusion versus multiple daily injections.
Results from studies evaluating the benefit of continuous subcutaneous insulin infusion compared to multiple daily injections have changed with the development of better devices and insulins. Initial randomized study by DeVries comparing the efficacy of continuous subcutaneous insulin infusion to multiple daily injections with NPH and regular insulin demonstrated reduction of hemoglobin A1c at 0.84% at 16 weeks with a modest increase in self-reported episodes of hypoglycemia with continuous subcutaneous insulin infusion. The DeVries study had a modest sample size with issues of dropout. A larger clinical trial called the 5-Nations trial performed in 11 European centers reported hemoglobin A1c decrease of 0.22% with a lower incidence of hypoglycemic events and higher user perception of satisfaction when comparing continuous subcutaneous insulin infusion to multiple daily injections using NPH. Development of long-acting insulin glargine prompted many to switch from NPH due to improved glycemic control, once-a-day injection, and stable drug action profile. When comparing continuous subcutaneous insulin infusion with multiple daily injections using glargine, the hemoglobin A1c and number of hypoglycemic episodes were similar, but the study did report a decrease in blood glucose variability using continuous subcutaneous insulin infusion. Preliminary studies have suggested that blood glucose variability to be the underlying pathophysiologic mechanism leading to diabetic complications, including nephropathy, retinopathy, coronary artery disease, and cognitive decline, although more research is needed to establish causation.
Indication for insulin pump therapy and benefits are clear for type 1 diabetes mellitus. However, for type 2 diabetes mellitus, the use remains debated and is often only considered after other methods have failed. Factors to consider for starting pump therapy include first and foremost patient desire based on the perception of the quality of life improvement, high activity level requiring changes in basal rates, history of hypoglycemic episodes, and women planning a pregnancy. The decision should be made after a conversation between the endocrinologist and the patient.
Insulin and pump technology will likely continue to develop at a rapid pace, improving the quality of life for patients living with diabetes mellitus. It will be challenging for healthcare professionals to stay abreast of every advancement, but a basic understanding of insulin pump delivery can help avoid common complications and improve outcomes.
The interprofessional team must maintain strong communication during the transition of care so that all are aware that the patient is on insulin pump therapy. Adjustments to the pump settings, including but not limited to insulin boluses, temporary basal settings, and other changes to basal rates, should be made by the patient or a certified pump specialist. Persistent hyperglycemia, problems with infusion sites, or removal of the device by the healthcare team should be rapidly communicated with the physician.
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