Evaluation of a Novel CGM Trend Arrow Adjustment Tool in Children & Adolescents With Type 1 Diabetes Using Insulin Pump Therapy and Continuous Glucose Monitoring (TAAT Study)

Continuous glucose monitoring (CGM) provides up to 288 blood glucose levels per day, updated every 5 minutes and displayed in real-time on the insulin pump, which can be used to enhance delivery of insulin through pump therapy. In addition this real-time CGM data includes "trend arrows" which indicate when the blood glucose is rapidly falling or rising thus enabling the pump user to make immediate adjustments in insulin delivery to prevent subsequent low or high blood sugars. The trend arrows are displayed when the blood glucose is rapidly falling or rising. For example, if the glucose is increasing by 1-2 mmol/L over 20 minutes, a single upward arrow alerts the pump wearer, who can then decide to give a bolus of insulin or increase the meal bolus. Should the glucose level be increasing at a rate greater than 2mmol/L over 20 minutes, 2 upward arrows are displayed and the user could decide to give a larger bolus. The purpose of the bolus adjustment is to add insulin for the predicted rise in glucose to prevent or reduce subsequent hyperglycemia. Similarly, a decrease in the insulin bolus is advised if glucose levels are falling as evidenced by one or two downward arrows.

However, effective strategies for adjusting insulin boluses based on CGM trend arrows are lacking. The JDRF CGM Study Group recommended that boluses be adjusted based on trend arrows using a standard 10-20% increase/decrease of the total original recommended bolus dose (10% for one arrow up or down, and 20% for two arrows up or down), with the original bolus dose calculated by the pump calculator (i.e. Bolus Wizard). However, the original recommended bolus dose is dependent on the amount of food to be consumed (grams of carbohydrate) and the current blood glucose (if above or below target range), as well as the amount of active insulin, and therefore increasing or decreasing the total recommended bolus by 10-20% may overcompensate for the trend arrows and result in postprandial hypoglycemia. Attempts to use the10/20% formula within CHEO's large pediatric pump/CGM population resulted in low acceptance and adherence by CGM users.

The CGM TIME Trial Study Group develop an innovative tool for adjusting boluses for CGM trend arrows based on the patient's own insulin sensitivity factor (ISF). The Trend Arrow Adjustment Tool formula is: if CGM shows a single arrow up or down: adjust bolus by +/- (1.5/ISF) and for 2 arrows up or down +/- (3/ISF). Use of the Trend Arrow Adjustment Tool within the CGM TIME Trial appears to lead to more appropriate adjustment in bolus dosing, and more effective prevention of subsequent hyper- and hypoglycemia. Furthermore, this tool appears to have excellent uptake amongst the TIME Trial participants, with observations that there is continued usage of the tool throughout the 12 month study, and greater satisfaction with this component of CGM. However, the tool has not been systematically evaluated.

The proposed study will evaluate the Trend Arrow Adjustment Tool, to determine its effectiveness in reducing postprandial hyper- and hypoglycemia, as well as parent, child/youth satisfaction, and ease of use of the tool based on self-report measures. Comparison will be made with the 10/20% bolus adjustment & also to no adjustments to meal boluses (i.e. ignoring CGM trend arrows). Should use of the Trend Arrow Adjustment Tool lead to more time spent within the target glucose range, this will have immediate clinical benefit for patients, including improved quality of life, and potentially a reduction in HbA1c and prevention of long-term complications.