Show Me the MOBI!
by Gary Scheiner MS, CDCES
In Melville’s epic novel Moby Dick, a behemoth creature torments a poor fisherman to no end. Well, a new Mobi has entered the pump pool, and it is a far cry from a tormenting behemoth.
Tandem’s Mobi insulin pump, combined with the Control-IQ algorithm and a continuous glucose monitor, represents the latest (semi) automated insulin delivery (AID) system. I include the word “semi” to remind folks that AID systems don’t do the job alone – they still require a fair amount of user engagement. As is customary, the Integrated Diabetes Services clinical team gave this system a real-world spin so that we can share our observations and offer up our unbiased opinions. So here goes.
The Tandem Mobi System Summary
In terms of functionality, Mobi is very much like its older sister, the t:slim.
The big difference: Mobi is much smaller and much, much lighter than a traditional pump. For comparison purposes, Mobi is about the same size as an OmniPod patch pump, but weighs about half as much. Due to its petite form factor, Mobi can adhere directly to the skin and connect to an infusion set with a discreet 5” tube (yes, there is still a tube and infusion set). For those who prefer to wear the pump in a pocket or clipped to a belt/waistband, traditional-length infusion set tubing may be used. Mobi’s disposable insulin cartridges hold up to 200 units of U-100 rapid-acting insulin and come with an adapter to ease the filling process. The pump has an internal battery that requires charging about every 4-5 days by placing the pump on a circular charging port for 15-20 minutes.
All programming is performed through a smartphone app. The only programming that can be performed on the pump itself is a manual bolus in fixed increments of either insulin units or grams of carb. The app sports an extensive range of programming features. Users create “profiles” for baseline insulin delivery and bolus calculations. Each profile includes basal rates, insulin-to-carb ratios, correction factors and targets – all of which can vary by time of day (although the target is fixed at 110 mg/dl when the pump is in automated delivery mode).
Mobi utilizes the same Control IQ insulin-adjustment algorithm as the T:Slim. It is a relatively simple predictive algorithm based on the current glucose value and direction it is headed. If the glucose is predicted to be above 160 mg/dl in 30 minutes, the basal rate is increased. Above 180, a conservative auto-correction bolus is delivered. The auto-correction bolus can be repeated as often as every hour. If the predicted value in 30 minutes is below 112.5, the basal is reduced. If the predicted value is below 70, the basal is turned off completely. Control IQ applies the user’s programmed basal rates as its starting point and adjusts from there. The magnitude of the basal adjustments and auto-correction boluses is based on the user’s correction factors, which reflect the user’s sensitivity to insulin. The user has the option to switch profiles as well as to deliver extended boluses while Control-IQ is running. Two overrides (called “activities”) can be used: An EXERCISE override, which makes the self-adjustment algorithm less aggressive, and a SLEEP override which makes the basal adjustments more aggressive but does not deliver auto-correction boluses.
Mobi is compatible with Dexcom G6 and G7 sensors. Plans are underway to also sync with the latest Libre sensor from Abbott. The CGM signal transmits directly to the pump (rather than having to go through one’s phone first). Since the Control IQ algorithm is programmed into the pump itself, automated adjustments take place whether or not the user’s phone is nearby.
There is a lot to like about the Mobi, starting with the pump itself.
The size allows it to be tucked away just about anywhere. But the weight (barely an ounce) is what truly impressed me. Due to the pump’s lightweight, the adhesive pouches provided by Tandem keep the pump stuck to the skin wonderfully, even with heavy sweating. I found that the double-sided adhesive patches used to hold the Eversense (implanted CGM) transmitters in place work great as well. It is nice having the option to wear the pump on the skin (with short tubing) or in a pocket/waistband (with longer tubing). For the latter option, Tandem provides a tiny clip case that is strong and secure. With either option, it is easy to disconnect and reconnect at the infusion site. And unlike a traditional patch pump, Mobi allows you to change just the infusion set without having to change the entire pump. I also like the adapter for filling the insulin cartridges. The adapter makes it easy to fill the cartridges without air bubbles.
Mobi, like t:slim, allows users a broad range of programming features even when the Control-IQ algorithm is running. Other AID systems don’t give the user the option to use advanced features when in “automated” mode.
For example, extended boluses may be programmed for large/high-fat/low-glycemic-index meals. Alternative basal/bolus profiles can be created and used for situations such as extended exercise, illness, stress, menstrual cycles, and long periods of sitting. And I love the fact that Control-IQ applies the user’s preferred basal settings as its starting point. Those with a pronounced dawn phenomenon (or evening growth phenomenon), or lower daytime or nighttime basal needs, don’t need to start rising or falling before the system does something about it. Having the right basal profile from the get-go helps to prevent the rises and falls. Most other AID systems apply a flat adapted basal profile as the starting point and wait until the glucose starts to rise or fall before adjusting.
The Control IQ algorithm offers the advantage of producing immediate benefits. There is no “adapting curve” like we see with other AID algorithms, and it isn’t influenced by short-term changes in insulin requirements such as illness, stress, menstrual cycles and changes in physical activity. The algorithm is simple, yet well-thought-out. The automated correction boluses can be a real asset for those who want to tighten their control without the burden of having to micro-manage. I also appreciate the way Tandem is transparent about how the algorithm works. As a clinician, it is important to see the adjustments that the system is making in order to come to appropriate conclusions, and Tandem’s app and software (Tandem Source) do just that.
Offering multiple CGM options is another plus. Once Libre compatibility is available (it already is with t:slim), Tandem will offer the widest range of CGM options for its users. And that’s important because different CGMs simply work better for different people. And having the data go directly to the pump, rather than the phone, offers a nice level of independence from having to carry one’s phone all the time. The bolus button on the base of the pump also provides some phone-freedom, particularly when it is set for entering carbs rather than insulin units (increments of 2, 5, 10, or 15g are available). When using the button for carb entry, the bolus is calculated by the pump based on insulin-to-carb ratios.
The Mobi phone app is a bit of a double-edged sword because currently, it is only compatible with iPhones. Android compatibility is coming, but for the time being, non-iPhone users are SOL.
As an iPhone user myself, that didn’t affect me personally. What did irk me is the sudden need to press a whole lotta buttons for even the simplest programming. Coming from the open-source (DIY) Loop system, I was used to a simple and very practical user interface. I could program and deliver a meal bolus in as few as 4-5 screen touches. Mobi takes more than twice as many. It may not seem like a big deal, but when you’re bolusing an average of seven times a day, it really adds up. Just to use the Mobi app, one MUST have their phone’s screen lock enabled (something I prefer not to use). That calls for 4 or 6 extra button presses just to open the phone. And the same unlock must be performed to confirm EVERY programming change and every bolus prior to delivery. Adding to the button-palooza, the Mobi app does not default to its “home” screen (called the “dashboard”), but to the last screen that was used – which is often the “clearing notifications” screen. So, one must navigate to the home screen just to get to the bolus menu every time the app is opened.
OK, maybe I’m being a little too sensitive when it comes to the extra button pushes. In some bureaucrat’s head, I guess that might provide an additional layer of safety. But there is also the issue of alerts and notifications that seem to be more of a nuisance than a benefit. The pump emits a beep (or vibrate) every time a bolus starts and finishes delivering. And any time a setting change is made. And every time the glucose is headed out of range (this is in addition to your usual CGM alerts). The user must go into the app to confirm each notification and see what the alert was for. And there is no way to disable all those extra beeps and buzzes. Again, that might just be me being a little too sensitive. But extra noises that don’t serve a meaningful purpose bother me.
While there are some great things about the Control-IQ algorithm, there are also some things I would like to see changed. For example, when Control-IQ is running, the target used for correction boluses is locked at 110. No way to adjust that unless you switch to “exercise” mode. Some people need and prefer tighter or looser targets. Likewise, the duration of insulin action used to estimate insulin-on-board is locked at 5 hours, which may result in over-calculation of IOB for many users whose insulin action dissipates in less than 5 hours. And while I love the fact that Control IQ applies the user’s preferred basal settings as its “starting point,” it means that the user and their clinician really need to fine-tune their basal settings to maximize the system’s performance. It’s a wise investment, but it does take work. One other thing: I found that the 30-minute glucose prediction for making automated adjustments may not allow enough time to circumvent lows and highs. Given that raising or lowering insulin delivery takes a few hours to have a meaningful effect, I would prefer to see a longer prediction time, as is the case with most other AID systems.
And just a few other miscellaneous issues I came across:
- The 200-unit cartridge volume (before priming the tubing) may not be sufficient for some users.
- For those who prefer the 5”tubing, no angled infusion set option is available – only a 90-degree soft canula and steel needle.
- The charging process can be awkward, since the pump has to sit on a docker for 15-20 minutes. For those using the 5”tubing, it will be necessary to disconnect while charging. Those who prefer to stay connected during the charging process have to be careful not to pull the pump off the docker, since nothing holds the pump in place. When traveling, the docker must be brought along since is a specialized device. And any alerts that cause the pump to vibrate while it is charging (such as suspending insulin delivery) may cause the pump to migrate its way off the charging docker.
- The pump emits audible “clicks” during delivery. Although they are muffled when the pump is worn under clothing, they are noticeable when the pump is clipped to outerwear.
- Those who prefer to use the adhesive sleeves to stick the pump to their skin will need to purchase additional sleeves on a regular basis.
Tandem Mobi – The Bottom Line
Now that I look at it, the vast majority of issues I had with Mobi were very minor… what some might call picayune.
Overall, this is a strong system. The pump has an amazing form factor. The self-adjustment algorithm works nicely. The phone app/user interface is easy to program and has a lot of nice features that other AID systems just don’t offer. And it’s nice to have multiple CGMs to choose from.
If you can get over some of the minor inconveniences, Mobi is an excellent system. Historically, Tandem has moved faster than other pump companies in terms of making software improvements and has always made those updates available to its customers for free.
For more information about, feel free to reach out to your Integrated Diabetes Services clinician (info@integrateddiabetes.com; 877-735-3648; outside N America: +1 610-642-6055), or contact Tandem directly: www.tandemdiabetes.com, 877-801-6901.
