Now that I have been using Auto Mode for the Medtronic MiniMed 670G for the last one-and-a-half years, I can say that spike control is one of the major weaknesses of this closed loop system.
Auto Mode does a decent job of controlling BGs for low to moderate glycemic index foods. But for high glycemic index foods, the pump struggles because of inherent Auto Mode safeguards.
As a safeguard against hypoglycemia, the pump pauses basal and microbolus delivery following meal bolus delivery for close to thirty minutes. This makes it very hard for the pump to catch up with a meal related BG spike.
In the photo snapshot, as soon as I bolus for my breakfast comprising a cup of tea and a piece of toast, there are purple dots dissapear for close to thirty minutes (purple dots signify every time the pump dispenses a microbolus or basal dose).
According to Medtronic, this period of no microbolus or basal delivery is needed to determine the BG trend after meal bolusing.
Even though the pump resumes microbolus and basal delivery, it is too late and the BG spike is inevitable.
Waiting longer than the 5-15 minutes before eating recommended by Medtronic somewhat helps. But it is still hard to recover from 30 minutes of no insulin delivery.
The reason manual mode is so good with spike control as compared to Auto Mode is because manual mode allows for a good balance between bolus and basal. The user can be able to adjust the basal does just right to assist the meal bolus counteract BG spikes.
Since Auto Mode is adaptive and conservative in nature, patience must be exercised and expectations curtailed to reasonable levels.
I can say it took me about a year to get to the point where I was comfortable with Auto Mode. And if you are hoping for a HbA1c of 5.7 with Auto Mode, it will not happen unless you are following a very compliant diet.
Realistically I would say that a HbA1c between 6.5 and 7.0 is easily achievable with Auto Mode without changing your pre-Auto Mode diet or habits.
But here are some tips from my experience on how to be successful in using Auto Mode to achieve the realistic HbA1c goals discussed above.
Get the new Enhanced Guardian 3 Transmitter (Version 2.2)
A lot of frustration for many users with Auto Mode arose from the defective first generation sensor transmitter that made it hard to enter Auto Mode due to the infamous “BG required loop”.
Medtronic resolved this issue with their new enhanced transmitter. I must say that I have had a lot of success with this new transmitter.
Using the upper thigh as a sensor insertion site, the guardian sensor is very accurate and in my view comparable to the Dexcom 5 which I used prior to getting the 670G. The new transmitter makes the CGM sensor experience even more pleasant.
The enhanced transmitter is a good foundation to finding success with Auto Mode since the more accurate the sensor, the better the control. The less the number of incessant errors and alarms at night, the higher the chance you will stick it out with Auto Mode.
To request for the new enhanced transmitter follow the link below:
I received the following message when my Diabetes educator ordered my enhanced transmitter.
Know your carb ratio(s) and master your carb counting
Knowing your carb ratio is very important since this is one of the two inputs that Auto Mode uses to keep your readings close to the Medtronic advertised BG target of 120 mg/dL.
Just remember, with Auto Mode, you will have to dial you manual mode carb ratio by about 1-2 points. So if your carb ratio is around 10 when you are in manual mode, it is likely that your effective carb ratio for Auto Mode will be somewhere between 8 and 9.
Having carb ratios really off will result in the pump becoming overly aggressive or really conservative. Over bolusing causes the pump to cut back on basal and micro bolus. For me if I go for long without the basal or microbolus, I feel fatigued and have to always deal with a spike if I end up eating during these periods.
Under bolusing will obviously lead to highs that will make it hard for Auto Mode to stay on-track.
Know that Auto Mode still requires discipline
Auto Mode does give you a little flexibility when it comes to your diet but it does not give you total freedom to do things you never did while in manual mode. For example, Auto Mode seems to get thrown off by constant snacking and bolusing. Constant bolusing really throws off basal delivery since the pump has to play a balancing act between basal and bolus to keep you within the 120 mg/dL target.
Similarly, Auto Mode requires mastery when it comes to eating foods with a high glycemic index or fatty food like pizza. It gets better with time but I normally exit Auto Mode and do dual bolusing when I eat such foods.
Do not try to trick Auto Mode
It is temping to give yourself a dose of bolus to correct high sugars under the guise of carb intake. Entering “fake or phantom carbs” really throws off Auto Mode.
Since Auto Mode assumes you ate with the bolus, it will continue to work hard to correct high sugars. What results is an accumulation of insulin that will cause your BGs to drop on the tail end of the insulin active time.
I have had scary lows at night as a result of trying to correct the high BGs right before bedtime outside Auto Mode’s recommended bolus.
Furthermore, the more Auto Mode keeps getting thrown off due to “fake carbs,” the more trouble you will have spiking and controlling hypoglycemic events.
If I must correct high sugars outside the recommended dose that Auto Mode suggests, I now exit to manual mode. Or else I just let Auto Mode take its time to getting me back on track.
Wait for 15-30 minutes to eat after Bolusing
I personally find waiting between 20-30 minutes helps with my post-meal spike control while in Auto Mode. The wait time is dependent on my pre-meal BG readings (longer times for higher BGs).
Auto Mode is not very good with Spike control as compared to manual mode and this can be a little frustrating. In manual mode, my basals and carb ratio are dialed down to a point where I have minimal spiking between meals.
Keep your Manual Basal up to date
It is important to make sure your basal patterns is still working well just in-case you have to exit from Auto Mode for a prolonged period of time due to illness or personal preference.
I am now making it a habit of exiting Auto Mode for two weeks every three months to optimize my basal patterns. This also seems to help my Auto Mode numbers.
This document by Medtronic for healthcare providers is the most detailed document I have read so far on Auto Mode and how to deal with different control scenarios.
Have a good Endocrinologist
Auto Mode and closed loop technology give us a glimpse of how complicated insulin pump therapy will become in the future. A good endocrinologist will keep up with the technology and help you fine tune your pump based on the training they continually receive from Medtronic or any other pump manufacturer.
As much as I hate going in to see my endocrinologist every three months, it has helped me achieve success with Auto Mode since it allows us to set short-term strategies that can be evaluated during very visit.
UPDATE - I have certainly found out that dialing the Carb Ratio and Active Insulin time up and down do not necessarily mean that you will get better control. That is why it is important to work with your endo or educator to tune these settings.
When it comes to Auto Mode for the MiniMed 670G, tuning the settings to get as close to your sugar targets feels a little more complicated as compared to the manual mode. This is because the closed loop system has a feedback mechanism which will likely throw-off one setting when you change another.
In the course of your day, the system is performing a balancing act between bolus and basal to keep you as close to Auto Mode’s fixed and preset BG target of 120mg/dL by introducing a third input – the micro bolus.
When it is all said and done, the user has control of two settings only, namely Carb Ratio (CR) and Active Insulin time (AIT).