What is the optimal insulin amplitude for a square wave bolus in people with type 1 diabetes

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BACKGROUND: In patients with type 1 diabetes insulin is required to control the rise in blood sugar levels that occurs after eating. Insulin boluses may be given in 3 main ways - a standard bolus (rapid bolus of insulin usually given just prior to a meal), a square wave bolus (a fixed dose of insulin given over a set period of time) or a dual wave bolus (a combination of the previous 2 boluses). AIM: To determine the amplitude (dose) required for a square wave insulin bolus of two hours duration to maintain blood glucose levels (glycaemic control) when a standard carbohydrate (60g) meal is eaten. METHOD: 40 participants between the ages of 7 and 35 years with Type 1 Diabetes on insulin pump therapy will be recruited. The inclusion criteria are HbA1C </= 8%, Body Mass Index (BMI) <91st percentile, no complications of their diabetes and no other medical conditions. During a 1 week lead up to the study blood glucose control will be closely monitored. Participants will be contacted daily-2nd daily by a member of the research team. Adjustments may be made to the participant's insulin pump settings in conjunction with their treating endocrinologist. A continuous glucose monitoring system (CGMS) will be inserted on the first morning of the study. On this morning the participant will need to come to the hospital prior to breakfast. They will check their BGL 1 and 2 hours after insertion of CGMS for machine calibration. Participants will be provided with standard breakfast containing 60g of carbohydrate for each of the 6 days of the study. Insulin for the breakfast will be delivered as a square wave bolus over two hours starting just before the person starts eating. The bolus rate will be based on the participant's insulin: carbohydrate ratio and randomised each day to deliver a different percentage of this ratio (1:1 i.e 100% of the participant's insulin:carbohydrate dose for 2 hours, 1:2 i.e 50% of the participant's insulin:carbohydrate dose for 2 hours, 1:3, 1:4 and 1:6). The 6th bolus will be the participant’s standard bolus dose delivered as per usual practice. After the bolus is completed participants will return the pump to their usual basal rate. Participants should not eat until 4 hours after the test meal. Participants will self-monitor their blood glucose levels (BGLs) according to usual practice. If BGL is >18mmol/L at any time from >/= 4 hours after breakfast a correction bolus will be used. If the BGL goes below 3.5mmol/L or the participant has symptoms of hypoglycaemia at any time then they will eat 15 grams of carbohydrate. OUTCOMES: Primary outcome is the blood glucose excursion at 1 hour. Secondary outcomes include maximal blood glucose increase, maximal blood glucose excursion, time to maximal blood glucose excursion, time in target blood glucose range, area under the curve and hypoglycaemic events.