Medtronic 780G Hybrid Closed Loop (HCL) system

• Carbohydrate counting – work to get this as accurate as possible
• Regular set changes – every 3 days if using a Teflon cannula and every 2 days if using a steel cannula
• Rotate cannula sites to avoid poor insulin absorption if the same site is over-used or lumpy

It is recommended to give the bolus 10-15 minutes before eating so that the insulin and food are absorbed at the same time and the bolus insulin will cover the meal most accurately. Mistimed meal boluses can lead to high post meal glucose levels followed by hypoglycaemia as the HCL will compensate if it detects a rapidly rising sensor glucose.

Generally less hypo treatment is required on these systems than on traditional insulin regimens. It would be worth reviewing sensor arrows and insulin on board to guide the amount of carbohydrate required, if any. It’s also worth noting that these systems will alert you that you are heading towards a hypo; the system will already have shut down insulin delivery to avoid the hypo and you should try to resist acting too quickly with carbohydrate top ups as this can result in overtreatment and rising above target. The low alert soon is a prompt to monitor your glucose more carefully and see if the system is levelling the glucose out or if you do need a small carbohydrate top up (3-7g) as well. See flowchart below for further guidance.

Remember your system is designed to keep your glucose in your target glucose range; if your glucose levels are running above this range for more than 2 hours and not coming down with corrections then it is likely your set / cannula has failed and should be changed

Refer to your sensor manufacturer and/or discuss with your educator which areas are good to place your sensor, usually on your tummy or back of the arm. It is worth investing in medical adhesive (Skintac® or tincture of benzoin) to ensure the sensor remains in place for the full 7 days. If your sensor requires calibration, try to at a time when glucose levels are relatively stable. Ensure you calibrate using a blood sample taken from a clean finger and high quality blood glucose meter. Avoid using the glucose reading from the sensor to calibrate. Avoid using sensors beyond their intended life span. NB Paracetamol can interfere with sensor readings; it would be advisable to monitor the accuracy of your sensor with additional fingerpricks when taking paracetamol.

The HCL function does not manage well when ketone levels are raised during illness. It is not able to meet the need for increased insulin requirements fast enough. For periods of illness where ketones are present (greater than 1mmol/L) turn your pump back to manual mode following sick day rules guidance in the pump handbook is recommended. This will involve the use of manual boluses and temporary basal rates which are not available in HCL. Manual mode is also the recommended option should a period on steroids be required.

Exercise is best managed either by:

• Using the higher glucose target 8.3 mmols temporarily; starting from 1-2 hours before the activity starts and for the duration of the activity

or

• Monitoring your sensor glucose more frequently during the activity and drizzling in small amounts of carbohydrate if you start to see downward arrows on your sensor. Avoid pre-loading with carbohydrate before exercise as this results in a rise in blood glucose that activates the automated basal to increase that can then lead to hypoglycaemia at the start of exercise.

or

• Using a combination of temporary higher glucose target and drizzling in carbohydrates

There is not much available information on managing alcohol in HCL and there may be a greater tendency towards hypoglycaemia if more alcohol has been consumed than is usual. In these situations it is recommended to switch to manual mode, use a reduced temporary target and have a carbohydrate snack before bed. Please talk to your educator for more specific guidance if needed

You should suspend the pump if disconnecting for longer than 15 minutes to avoid the system accounting for insulin not delivered

You may have been tempted in the past to add pretend carbohydrates to your pump to bring a high blood glucose down when corrections haven’t worked well enough. This approach does not work in HCL and will increase the risk of a hypo.

You can get a lot of data when using HCL. Over time this will become more familiar and useful to you. Your educator can help you interpret what the reports mean and how to make adjustments. The reports also present your glucose data in a different way; in addition to predicted HbA1c (GMI) you will get time in range. You are aiming for at least 70% time in range (3.9-10 mmol/L) with less than 4% below 3.9mmol/L and less than 1% below 2.8mmol/L. Every 1% more time in range is the same as another 15 minutes with blood glucose in range so even small changes make a difference to your health.