Insulin pumps have come a long way since their introduction with almost 45% of our paediatric patients in WA currently on this therapy. Pumps deliver short-acting insulin continuously through a subcutaneous cannula that is re-sited every third day. The basal insulin delivery is set to mimic endogenous insulin production. Prandial and correction boluses are administered via the pump under user control

Dr Mary Abraham, Paediatric Endocrinologist, Princess Margaret Hospital

Further advancements are directed towards glucose monitoring and improved pump algorithms to reduce hypoglycaemia. Table 1 lists devices currently available in WA.

Continuous glucose monitoring (CGM) systems

CGM systems empower patients to improve their diabetes management. A subcutaneous glucose sensor, re-sited every 6-7 days, measures interstitial glucose every five minutes. The sensor is attached to a transmitter which sends these readings to either an insulin pump or a receiver (patients on insulin injections), providing real-time continuous display of glucose readings. Calibration for optimal functioning uses capillary blood glucose measurements to transform the sensor signals from interstitial fluid into glucose values.

Regular CGM use is associated with improved glycaemic control and with reduction in severe hypoglycaemia and overall health costs. CGM is beneficial for patients with frequent, severe, or nocturnal hypoglycaemia, especially with impaired hypoglycaemia awareness.

However, until recently prohibitive costs have limited CGM uptake. The Australian Government has now made available through the National Diabetes Service Scheme, subsidised CGM products to children and young people with type 1 diabetes (below age 21).

The current CGM systems are more accurate and precise, reasonably unobtrusive and small. Some devices share the sensor glucose readings with family or friends (Dexcom G5, Medtronic Guardian Connect).

The systems reduce the number of finger pricks, provide real-time information on glucose, provide trend arrows and alerts, and enable the user to treat actual or impending hypo- and hyperglycaemia. Some systems are also approved for use in insulin dosing decisions (Dexcom G5).

Flash glucose monitoring system

A flash glucose monitoring (FGM) system (Libre, Abbott), recently introduced, is small and compact, does not require calibration by the user, and has a two-week period of use with good accuracy. This approach provides glucose levels intermittently when scanned by the user using a receiver or an Android smartphone, but currently cannot provide alarms or control insulin infusion rates.

Sensor-augmented pump therapy

Algorithms incorporated into sensor-augmented pump therapy focus mainly on reducing hypoglycaemia. The Low Glucose Suspension (Suspend on Low) suspends basal insulin when sensor detects hypoglycaemia and reduces time in hypoglycaemia. Predictive Low Glucose Suspension (Suspend before Low) suspends basal insulin with the prediction of hypoglycaemia and prevents it occurring.

These systems are available in the Medtronic MiniMed 640G pump when used in conjunction with the Enlite sensor.

Where are we heading?

The ultimate aim is to have a fully-automated closed loop system that uses a control algorithm that autonomously and continually increases and decreases the insulin delivery in response to real-time sensor glucose levels.

Closed-loop artificial pancreas systems have been under development for several years with numerous algorithms, and are being tested in, camps, supervised outpatient settings and free living conditions.

A hybrid closed loop system using the Medtronic 670G pump (FDA approved in USA) is under trial in Australia – it delivers insulin based on sensor glucose levels but needs the user to bolus for meals.

Challenges

The systems require ongoing user involvement as well as experienced and informed diabetes teams for successful adoption. The ‘patient-medical device interface’ is a complex paradigm, and central to success is the adherence, understanding, and engagement by the patient with the technology. The need to wear an additional device, troubleshooting sensor problems, and coping with alarms and alerts are potential barriers to uptake.

Ultimately, treatments should always be individualised and health care providers focused on achieving glycaemic targets by whatever means best suitable to the patient.

Table 1: CGM Technology in the management of Type 1 Diabetes

*not approved under NDSS

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