Caution – before you start looping

When I started looping with OpenAPS I needed ‘head space’ and time to learn, to monitor my blood glucose levels closely and adjust my settings. I kept a very close eye on my CGM. When I switched to Loop one year later, there was a whole new learning curve. You do have to be vigilant whilst setting things up and getting used to a new system.

Howard, Look, CEO of Tidepool, has just released this caution to the Facebook group, Looped. It is especially relevant to parents of children.

Please read this before you start looping. In Howard’s words… “This post is intentionally blunt and potentially scary.”

“I am posting this as a Dad who happens to have a daughter with T1D who has been using DIY Loop for some time – coming up on 3 years. (I also happen to be CEO of Tidepool. This post is about DIY Loop and is coming from me as a DIY Loop Dad.)

DO NOT USE LOOP if you do not understand the settings.
IMPROPER LOOP SETTINGS COULD KILL YOU OR YOUR CHILD.

The Loop algorithm relies on settings to determine how much insulin to give. These settings are exactly the same as the settings you might have in an insulin pump using traditional (a.k.a. open loop) therapy. Loop also has two additional settings that aren’t found in traditional therapy.

If you or your clinician do not understand what appropriate values are for these settings, do not just set up Loop and use numbers that you don’t understand and assume that everything will be OK. Doing so could cause Loop to give an overdose of insulin, and an overdose of insulin can cause a seizure, coma or death.

DIY Loop does not currently put any limits on settings, so you need to be really careful and make sure you don’t enter values that could cause dangerous amounts of insulin to be delivered. Here are some examples:

Correction range: This used to be called “target range” in previous versions of Loop. It is the range that Loop tries to keep your blood glucose in. A correction range of 100-120 mg/dL (5.5-6.6mmol/L) is a reasonable range. To be even more conservative you might want 110-130 (6.1-7.2) or even 120-140 (6.6-7.7).

A correction range of 20-40 mg/dL (1.1-2.2mmol/L) is NOT a reasonable setting for anyone, and is extremely dangerous.

(Mary Anne here: I used 120 mg/dL (6.5-6.5mmol/L) as my correction range (BG target) when I first started looping and only reduced it to 100mg/dL (5.5mmol) after a few weeks once I had reassured myself that the settings were working safely.) 

Insulin Sensitivities: This is also called “correction factor” in your Omnipod PDM. This is the amount of BG drop that insulin will cause. 50 mg/dl/U (2.8mmol/L/U) means that 1 Unit of insulin will cause a 50 mg/dL (2.8mmol/L) drop in BG. That’s pretty typical for an adult. Kids are typically much more sensitive, meaning insulin causes more of a drop. It’s not uncommon to see have an ISF of 80 (4.4), 100 (5.5) or 120 (6.6) in kids. Higher numbers are more conservative.

An Insulin Sensitivity of 1 mg/dL/U is NOT a reasonable settings for anyone, and is extremely dangerous.

Basal Rates: These are the underlying level of insulin that your body needs, and it typically varies slightly over the course of the day. Kids often have basal rates in the range of .25 Units per hour to .50 Units per hour. Adolescents may go up to 1.0 Units per hour. Adults are typically in the .75 to 1.0 range.

A default basal rate of 10 Units per hour is NOT a reasonable settings for anyone, and is extremely dangerous.

Carb Ratio: This is how many grams of carbs are “covered” by one unit of insulin bolus. If you don’t know your carb ratio… wait – don’t start Looping yet. Speak to your endo or health care provider to determine your value. You should not just enter a “placeholder” value without having some idea if it is representative of your insulin needs.

These are just a few examples. Again, if you do not have insulin pump settings that you already trust or think are at least close to accurate, do not just start Looping! If you do, make sure you put the right settings in the right places. Don’t get Correction Range and Insulin Sensitivities mixed up.

This blog post may be helpful to you to understand if your pump settings are similar to what other people use. As will be clear if you read the article, there are wide ranges for every setting, for every age, so you really should test your settings and work with your care team:

https://www.tidepool.org/blog/lets-talk-about-your-insulin-pump-data

This web site has great tips on how to test and optimise your settings for Loop:

https://looptips.org .

The Looped Facebook group also has hundreds and hundreds of posts/comments encouraging people to test their settings prior to using any DIY looping system, please respect that advice.”

(Mary Anne here: Please note that some adults can be very insulin-sensitive too. One unit of insulin reduces my blood glucose levels by over 9mmol/L (162mg/dL). As someone with extreme insulin sensitivity I have seen first hand how much variability can occur and how difficult getting meal boluses right can be. Better to be conservative and safe, especially with your precious children.

Another factor that needs to be right for safe looping is Duration of Insulin Action (DIA). Please read Tim Street’s excellent blog post on ‘Why we are regularly wrong in the duration of insulin action (DIA) times we use, and why it matters‘ before you set your DIA.

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