Will the First Approved Automated Insulin Delivery System Be a Game-Changer in Type 1 Diabetes Management?

Abstract

I n a person without diabetes, glucose is maintained in a very narrow range. To accomplish this, beta cells have a clever mechanism by which they respond to rising glucose levels with increased insulin secretion. As glucose levels rise, more glucose is metabolized by the beta cell, which in turn stimulates insulin secretion. In contrast, people with type 1 diabetes (T1D) must rely on insulin delivery via injections or via an insulin pump. As stand-alone devices, insulin pumps lack an automated feedback mechanism by which to adjust insulin delivery rates. They have set basal rate profiles and rely on users to input grams of carbohydrate and glucose values to determine insulin bolus amounts.The commercial availability of continuous glucose monitoring (CGM) starting in 2000 dramatically changed the options available to manage diabetes. 1 These devices allow for viewing of sensed glucose values in real time. But what has been lacking up until recently is the availability of automated insulin delivery systems, which modulate insulin delivery in response to sensed glucose values. Often these systems are termed artificial pancreas systems, although this term is somewhat misleading as these systems typically only deliver insulin, do not mimic the other functions of the pancreas, and lack many inputs that control hormone secretion of the normal human pancreas. 2 The first system to provide some form of insulin automation was the Medtronic 530G with Enlite. This system includes a threshold suspend feature, such that when the sensed glucose value drops to a certain threshold (settable between 60 and 90 mg/dL), the system alarms. If the user does not respond to the alarm, such as while asleep, insulin delivery is suspended for 2 h, or until manually resumed. In a study of 247 patients with documented nocturnal hypoglycemia, the threshold suspend feature significantly reduced hypoglycemia; the percent time of the sensor reading <50 mg/dL was decreased by 57%. 3 However, the Medtronic 530G system was not designed to prevent hypoglycemia, only to reduce the severity and duration of hypoglycemia once it occurs. The Medtronic 640G system was designed to prevent hypoglycemia using a predictive low-glucose suspend (PLGS) feature. With this feature, when hypoglycemia is predicted using a linear prediction, insulin is automatically suspended and then resumed again once the sensed glucose is predicted to rise above a set threshold. 4 In a study of children with T1D, use of PLGS reduced the percentage of time with sensed glucose values <70 mg/dL by 54% in children 11-14 years of age (10.1% on control nights to 4.6% on intervention nights) and by 50% in children 4-10 years of age (6.2% on control nights to 3.1% on intervention nights). 5 Although the 530G and 640G systems significantly reduce hypoglycemia, they were not designed to address hyperglycemia. Uncontrolled diabetes remains the leading cause of kidney failure, lower-limb amputations, and adult-onset blindness. 6 In data collected by the T1D Exchange, the vast majority of yout...

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