Too frequent basal updates may cause basal insulin delivery problems with Omnipod Dash

[SetaHemuli]

• AAPS version 3.3.1.3
• Using closed loop with SMB enabled
• Pump: Omnipod Dash
• Glucose sensor: FSL3
• BG values coming every 1 minute from Juggluco

Problem description:

Too frequent basal rate changes may cause basal insulin delivery problems when using Omnipod Dash pump (may also affect other pump models).

Omnipod Dash uses a timer for giving small 0.05u doses of basal, with an interval defined by set basal rate. For example, basal rate of 0.6u/h results in 0.05u dose of insulin given every 5 minutes. Dose is given at the end of each timer interval, ie. if basal rate is set to 0.6u/h, the first dose will be given after 5 minutes have elapsed since setting basal rate.

When using 1-minute blood glucose values from Juggluco, AAPS loop updates once every minute. This may lead to basal rate changes happening once a minute. Every time basal rate is updated to the Dash, also the timer on the pump is reset to zero. If basal rate is changed too often, it may lead to a situation where zero basal is actually delivered, since the pump timer keeps resetting.

I have verified that insulin delivery from the Dash indeed stops by changing basal rates too often. I disabled AAPS Loop, and manually changed temp basal rates from AAPS about once every 30 seconds. Basal rates were changed from 0.8U/h to 3.0U/h. By continuously switching the basal rate, no insulin was delivered for a full 10 minutes (verified by listening for the "click" sound the pump makes when delivering 0.05U).

Suggestions for improvement:

• Disable 1-minute Loop updates when using Omnipod Dash pump. Only allow loop updates / basal rate changes once every 5 minutes
• Include a warning in AAPS documentation which describes that 1-minute BG updates may lead to incorrect basal delivery, particularly when using Omnipod Dash pump