Starting Loop: Settings

Settings are very important! Loop does math every 5 minutes to make predictions and recommendations on raising basal, lowering basal, delivering a bolus, suspending delivery of insulin, and more. If your settings are not right, Loop will be making the wrong predictions which can lead to bad and sometimes dangerous recommendations.

Does this look familiar – it should.  You’ll find these words repeated several times, in a variety of ways, throughout this website and the Diabetes Online Community.

This article provides a high-level answer to these questions:

• Why would my settings with Loop be different from my current settings?
• What if I’m switching to Pods from a tubed pump?

Why Would My Settings with Loop be Different from My Current Settings?

Most people move to Loop assuming they can just transfer their settings from their pump or PDM.  Even if your settings resulted in 100% TIR (time in range) using your prior insulin delivery method, they will most likely need to be adjusted to work with the Loop algorithm.

This page goes over the three pillars: Basal, Insulin Sensitivity Factor (ISF), and Carb Ratio (CR).

There’s more to it than that, and you’ll find links to many settings suggestions as you keep going. Many of these suggestions are valuable whether you use a closed-loop system or are pumping and using a CGM in the “traditional” way.

An important concept to keep in mind as you’re reading this is that each setting must stand alone.  You shouldn’t be increasing basal, when you need a lower carb ratio or insulin sensitivity factor.

Basal Rate

• Loop uses the difference between your scheduled basal rate and what Loop has been giving you to calculate Insulin on Board (IOB)
• If your basal rate is too high
  • You may have it set this way to cover meal portions (fat/protein) or small snacks
  • Loop will think you need extra insulin when you don’t and your BG will tend to run below target
• If your basal rate is too low
  • Loop will expect your BG to drop and may restrict basal
  • Your BG will tend to run above target
• If your basal settings were really good pre-Loop, they will remain good

Insulin Sensitivity Factor

• Loop uses an insulin model, based on published research, for the type of insulin you select
• All insulin models have a long, low-level tail that stretches out ~6 hours depending on the type
• Manual pumpers only need to consider the first 3 to 4 hours of DIA (duration of insulin action) because they may be correcting at meals and maybe once between meals
  • The pump DIA model is a linear fall-off of activity, and does not include the exponential tail of around 15% (varies by insulin type)
• The small amount of insulin action in the long tail matters to the every-5-minute calculations that Loop makes to predict future blood glucose out to DIA in the future
• Many Loopers discover they need to raise the number for their ISF (even if their correction factor was perfect when pumping manually)

Carb Ratio

• Loop allows you to input the expected absorption time for the carbs and when you plan to eat them
• Many loopers add in the effects of protein and fat along with carbs as an Effective Carb amount
  • If you’ve been using Temp Basals or Extended Bolus to handle meals, you’ll need to learn a new protocol.  These videos should help.  There is NO extended bolus in Loop.
• Once you figure it out – you will probably wonder how you ever did it before – but there is a learning curve

Carb Sensitivity Factor

• Ratio of ISF over CR
• Represents the impact of 1g of glucose on your blood glucose level
• Should be consistent regardless of time of day, so both ISF and CR changes should move in the sam edirection

What if I’m Switching to Pods from a Tubed Pump?

Many new Loopers switch to Omnipod in order to Loop. Loop-main (also known as Loop 3) supports both Omnipod Eros and Omnipod Dash.

• Pro: you can use an in-warranty pump with Loop
• Con: if you have not previously been using pods, there may be a transition period

New Podders

• You can use either DASH or Eros pods with Loop-main
• You do not need to purchase a PDM
• Build Loop and use Loop to control the Pod
  • See Starting Loop with Rufus
• Once you attach a Pod with Insulin to your body
  • Use Loop in “Open Loop” mode to get your settings adjusted; this means that, at first, you will be pumping as any Omnipod user without the benefit of Looping while you get used to using the Omnipod system
  • The cannula for the pod may provide different absorption at the site, so you may find that some of the settings you had with a tubed pump need fine tuning as you transition carefully to the Pods
  • You might need to adjust your basal rate –  carefully test your basal settings
  • After you are confident in your basal settings, you can work on your other settings
• Only when you are confident in your settings should you transition to Closed Loop

Additional Reading

Please take the time to read the docs, do testing in Open Loop mode and, once you switch to Closed Loop mode, pay attention.

See this reference on DIA: Confusion Regarding Duration of Insulin Action, A Potential Source for Major Insulin Dose Errors by Bolus Calculators

An excellent reference for getting prepared with your settings is this LoopDocs page.