Being On Call for Type 1 Diabetes with Carer

Managing my 5yo son’s Type 1 Diabetes (T1D) at night is a lot like being on call as a software engineer. Both are absolute shite. Waking up to alarms at all hours, trying to fix something to only make it worse, not understanding why anything is happening, alarm fatigue, lost sleep, burnout, and the constant stress you will sleep through an emergency.

It is a bit guff to compare the two. Though, there are a some things that do apply to both, like good tools can reduce the burden.

So I built an app called “Carer” to simplify decision making and reduce alarm fatigue. This post is about building Carer and about the thinking that went into it. This post is not healthcare advice.

Who is Carer for?

Carer is an app that displays information and triggers alarms based on data from a Nightscout instance. Nightscout is an open-source, self-hosted individual repository of T1D data that has wide adoption in the DIY diabetes community for monitoring and remote care.

Carer can also send information to Nightscout, like consumed carbs or temporary targets. This information is synced down to the artificial pancreas system (APS), like AndroidAPS, to make decisions about insulin delivery.

If you use Nightscout, and especially AndroidAPS, Carer is for you. Carer is available on iOS, macOS and Android (15+). It is free forever with no ads.

The Basic T1D Management Loop

To understand why Carer exists, you must know the basics of being on call for T1D. The main goal is keeping Blood Glucose Level (BGL) between 4–10 mmol/L by:

1. Giving Carbs (e.g. gummy bears) to make BGL go up in 20–30mins.
2. Giving Insulin to make BGL go down in 20–60 mins.

The time it takes for insulin and carbs to take effect is imprecise and can affect BGL for many hours.

Using these two levers to achieve stable blood sugars results in the T1D management loop:

1. Look at Blood Glucose Level (BGL) every 5 minutes, which is the frequency of BGL readings from a continuous glucose monitor (CGM).
2. If Low (< 4) or going low: Give carbs
3. If High (> 10) or going high: Give insulin
4. Wait 20–60 mins for carbs or insulin to take effect
5. GOTO 1

This loop is a balancing act between insulin and carbs 24/7, sleep is not a respite. This is a pretty basic description of a complicated process, but it gives a good starting point for designing an app.

Basic App Requirements

To implement a tool to help with the above loop, it would need to show:

1. BGL so that is easily readable.
2. BGL trend up/down both as a diff between the last two readings and as a longer trend, to help predict highs or lows.
3. History of carbs and insulin to calm nerves when waiting and to stop any double dosing.
4. Information that affects decision making like insulin and carbs on board.
5. Time since last reading so you know when the next reading will be.

Making this information available by turning the phone into an always-on display will make checking BGL every 5 minutes much less disruptive. At night this display should dim as low as possible while still being legible as studies [1][2] show that light at night may be detrimental to health.

The app should alarm so that you don’t have to focus on the numbers during the day and so that you wake up when asleep:

1. Alarm the user when high, low, urgent high, urgent low, fast drop and fast rise.
2. Alarm when no BGL data have been received for a time. This is a catch-all alarm indicating a lot of problems.
3. An alarms sound should be an increasingly loud noise and there should be a bright flashing screen so as not to wake the whole house.
4. Ability to snooze Alarms when waiting for carbs or insulin to work.
5. Predictions of BGL can be used to implement predicted low alarm and smart-snooze when predicted to soon be in range.
6. Customisations for all alarms and alerts should be available, as each person manages their T1D differently.

Adding carbs and insulin is tricky. In the future we may be able to raise blood glucose remotely using a dual hormone pump, but these are unavailable at the moment. Giving insulin remotely is possible, but very dangerous, so instead you will have to use other methods for this. What the app can do is adjust the APS algorithm by:

1. Writing down given carbs that will increase insulin delivery.
2. Changing the target BGL that will increase or decrease insulin based on target and current BGL.
3. Swapping to a preset profile, which changes the settings that the APS algorithm uses to calculate dosage.

Experience to Features

When I started using Carer I was always on the lookout for how to make it better. Here are a few examples of features that came from something going wrong:

1. One night our son unplugged his phone’s charging chord, so his phone slowly ran out of battery overnight. Eventually it turned off, shutting down and causing a no data alarm after 20 minutes. Carer shows if his phone isn't charging, and alarms if it gets to a low battery.
2. On a few occasions I have woken up to an alarm that I had zero recollection of snoozing. Apparently, I had learnt to snooze an alarm in my sleep. Carer forces the snooze button to be a long press, making it just annoying enough to wake up a little bit.
3. I woke up to a low alarm, gave carbs then snoozed the alarm. The low turned into an urgent low and my son needed more carbs, but the alarms were snoozed and I was asleep. Carer will wake up from a snooze if a low turns into an urgent low.
4. Once I gave too much insulin, then snoozed for too long. My sons BGL dropped until he was low 30 minutes later. It was snoozed so it didn’t alarm for the low. Carer will turn snooze off if not alarming for 20mins.
5. Every 3 days Sam needs his Omnipod insulin pump replaced. One day we forgot and only realised after he had fallen asleep. Carer shows upcoming changes for pumps (every 3 days) and CGMs (every 10 days).
6. Fell asleep with notifications silenced: Show when notifications are turned off
7. Fell asleep with volume down: Alarms override system volume
8. Misclicked buttons: Better UI and UX
9. Phone was locked but still want to be notified of alarms: Use background task to notify of alarms (only runs at most every 15 mins, so is not reliable)

As I added each one of these features, I was able to relax a bit more as something that was stressful and that I had to have in the back of my mind all the time was resolved.

Thanks to my wife for being the first user; Diego for helping me clean up the UX, beta testers for finding so many issues.