Hybrid closed loop pointers

Set changes

We recommend set changes every 3 days, and those using steel cannulas should change every 2 days.

If sets are kept in place for longer than this then the absorption of insulin from the site becomes less effective. This often leads to glucose readings above target.

Remember to rotate your cannula sites. Repeated use of the same sites will lead to problems with insulin delivery.

If you are using HCL therapy and your glucose readings are rising above target despite the system delivering more insulin, you should assume the problem is with your infusion set and change it ASAP.

Boluses

Number of boluses per day

When you are using an insulin pump you should aim to bolus for all meals and snacks. Being on HCL does not replace the need to bolus. We therefore expect most children and young people to bolus at least 5 times per day. Generally, we do not expect those on HCL to do extra manual boluses for corrections, unless something unusual has happened like a set failure.

Timing of boluses

Even rapid acting insulin, such as novorapid, still takes time to be absorbed from the subcutaneous tissues. In order for boluses to be most effective they should be delivered before eating. This is arguably even more important for those on HCL as discussed further below (see bottom section).

Average carbohydrate intake per day

In order to be confident that you are remembering to bolus for all of your meals and snacks, you can look at your average carbs per day entered through your pump. The table below broadly lists what we would expect children of different ages to consume, although of course everyone is slightly different.

Time spent in automode

“Automode” is when your pump and sensor are communicating with each other and your insulin is being adjusted automatically. If this stops working, your pump will revert to “manual mode” and the pre-programmed settings. Reasons for this could include:

• loss of connectivity between pump and sensor
• failure to calibrate your sensor with a fingerprick blood glucose check when asked.

You should aim to spend more than 90% of your time in automode. If this is not the case, then it is more difficult to draw conclusions from your HCL data.

Time in range (TIR)

This refers to your percentage time spent with glucose readings 3.9-10mmol/L.

You can assess your TIR by looking at 14 days worth of data. Ideally to draw conclusions you should be using your sensor more than 90% of the time.

International recommendations are to aim for a TIR of 70% or higher. This is the same as being in target for just under 17 hours a day.

Time below range

International recommendations are to aim for a time spent low (sensor glucose less than 3.9 mmol/l) of less than 4%, and very low (sensor glucose less than 3.0 mmol/l) of less than 1%.

Time above range

You should aim for a time spent high (sensor glucose 10.0 to 13.9 mmol/l) less than 25% of the time, and very high (sensor glucose more than 13.9 mmol/l) less than 5% of the time.

These recommendations are all summarised in the figure below:

Variability

Standard deviation (SD) is a measure of glucose variability. Somebody with lots of highs and lows may have an average glucose which looks ok, but have a high SD. The same concept is expressed as a percentage in the "Coefficient of Variation". Aim for an SD number of less than a third of your average sensor glucose, which is the same as a coefficient of variation of 33% or less.

AGP report

Another good visual guide for interpreting your glucose data is to look at the AGP report. This usually contains a graph of your average glucose readings plotted over a 24 hour period. It allows you to quickly see which times of the day you are likely to be in range, and when you are more likely to have low or high readings. There is an example of this below:

Consider your personal “diabetes burden”

One of the main reported advantages of HCL therapy is to reduce the burden of managing diabetes on the person and family. It can be helpful to think about these aspects:

• Less user interaction. Ideally a person should interact with their devices for no more than 10-20 minutes per day. This should be sufficient time to manage your set changes and mealtime boluses.
• Low alarm burden. Alarms should trigger an action. If you find yourself repeatedly silencing an alarm, or becoming frustrated with alarm frequency, then discuss this with the team as there may be options to reduce this.
• Low device burden and low rate of technical issues. If these are an issue then it may be worthwhile discussing these with the DOT team or phoning technical support. We don’t want technical issues to be a barrier to anyone using HCL therapy.

Consider settings

The different HCL systems all use slightly different algorithms to adjust your insulin. It is therefore helpful to understand the system you are using, and what can and cannot be adjusted. The table below gives a summary of this:

External Links

CamAPS FX website

Medtronic Smartguard website

Tandem ControlIQ website

Omnipod 5 website

Time below range too high?

• Ensure accuracy of carb counting and pre-bolusing. If you are certain of these two things then consider weakening your insulin:carbohydrate ratios.
• Revisit the timing of your boluses. If you bolus late, your system will have already increased insulin as you start to absorb glucose into our bloodstream. If you then bolus for your carbs then this can be equivalent to a double bolus, and you will get too much insulin. The effect of this can be late hypoglycaemia after eating.
• Hypos during sleep. This is uncommon on HCL therapy. Consider using a higher glucose target overnight. You may also find that having a smaller supper may help, as large suppers will result in larger boluses or increased automated insulin delivery at the start of your night. This puts you at greater risk of hypos.
• Changing your ICR. See table below for guidance on how much of a change to make:

Time above range too high?

Firstly, always ensure your set is working and you are in automode.

HCL systems generally perform very well during periods of fasting, so hyperglycaemia is most common after eating.

• Ensure boluses are not being missed, and are being administered before food.
• Ensure carb counting accurate.

If you are certain of these 2 things then consider strengthening your insulin:carbohydrate ratios by referring to the table below:

Too much time above target overnight?

• Consider what is happening in the evening before you go to bed. Revisit your evening bolus history.

Time above target unrelated to eating?

• If hyperglycaemia is definitely not related to eating (e.g. happening all throughout the night), then consider whether your glucose target should be adjusted (Medtronic/CamAPS), a temporary mode can be used (Tandem: sleep mode) or your basal rates adjusted (Tandem).

Do high readings follow low readings?

• If so then re-visit hypo treatment. When using HCL you are very likely to require less quickly absorbed glucose to manage hypos. This is because the system will already have reduced the insulin flow for predicted or actual hypoglycaemia. If you combine this with your usual hypo treatment then this is likely to be too much and you will overshoot.

Automated Insulin Increased after food?

Not enough automated insulin?

If automated insulin delivery is consistently increased after a meal, this likely means your ICR is too weak. The system is having to “work hard” to get you back down into target. This is illustrated in the diasend screenshot below, which shows that around 6 additional units of automated basal insulin is being delivered after breakfast.

In this example the result of this is a delayed “near hypo”. It would be better to deliver more insulin as the up-front bolus to avoid this by strengthening the carb ratio:

Automated insulin shutting off after food?

Too much automated insulin?

If automated insulin delivery is consistently shutting off after a meal, this likely means your ICR is too strong. The system is shutting off to try and prevent hypos. This can be shown below.

You can also see in this example that the user has applied the “ease off” function, as shown by the yellow hatchings. However automated insulin delivery has already stopped completely and so “ease off” will have no impact. This ICR should be weakened:

Hypo management

Overtreatment of hypos on HCL therapy can lead to a frustrating “see-saw” pattern of glucose readings. This is because the system will have already reduced or suspended insulin flow for your predicated hypo, so if you take a full hypo treatment you are likely to overshoot. The system then recognises your glucose readings are going above target and increases insulin again, which can result in a further hypo. This is illustrated in the graphic below, which shows hypos occurring at 0130, 0600 and 1230. If you look at the automated basal insulin delivery after each of these episodes, you can see around 8 units of extra insulin being delivered:

If you are somebody who feels very hungry when hypo, a safer strategy would be to take enough hypo treatment to get into target (e.g. 5g of quick acting carbohydrate every 5 minutes), and then have a follow-up snack paired with an insulin bolus.

Timing of boluses

We recommend bolusing 10-15 minutes before you eat, and many people find they need longer than this at breakfast time, when their body is the most resistant to insulin.

If you bolus late on HCL therapy, for example after you have started eating, the system will have already recognised your glucose readings rising and increased your insulin flow. If you then take your full mealtime bolus then this can be too much, and puts you more at risk of hypos after your meal. If you realise that you have forgotten a bolus, it can be a safer strategy to take half of your bolus (for a large meal/snack) or even to omit your bolus it if you have just had a small snack.

Exercise

The different HCL systems all use slightly different algorithms to adjust your insulin. It is therefore helpful to understand the system you are using, and what can and cannot be adjusted. The table in the previous section describes this.

Loading up on carb-rich snacks to fuel exercise is not a good strategy when on HCL therapy. This is because it will lead to you glucose readings rising, and your automated insulin delivery increasing. This puts you at more risk of hypos. Consider using exercise mode, a temporary target or the “ease off” function, depending which system you are on. Ideally this should be commenced 90 minutes prior to activity but it is better to put this on at the last minute than not at all. You can consider taking very small amounts of carbs regularly during exercise, but not enough to result in a blood glucose rise as this will trigger an insulin rise.

Disconnecting

We recommend suspending insulin delivery from your pump if you plan to be disconnected for 15 minutes or more. If you leave your insulin pump running when you disconnect, your HCL system will still be responding to signals from your CGM and potentially trying to adjust your insulin. Depending which system you use, there may be a degree of artificial intelligence or “learning”. It is therefore better not to confuse your system by remembering to suspend.

Alcohol

Loading up on carb-rich snacks before bed is not an advisable strategy for avoiding hypos when drinking alcohol. Again, this will result in more insulin being delivered and will increase your risk. Consider using activity mode or a setting a higher temporary target when you go to sleep after drinking alcohol.