A Scientist's Life on the Medtronic MiniMed 670G Insulin Pump and More.

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Category: Basal Settings

Shortcomings of the medtronic minimed 670g, automode and guardian sensors

From the onset let me say I love the Medtronic MiniMed 670G and the Auto Mode setting. Closed loop insulin pump technology is the technology of the future. Personally I foresee the insulin pump becoming an install-and-forget type of medical device in the near-future. While in no way perfect, the first iteration of the MiniMed 670G was a great step forward in this direction.

Here are some design issues that make the pump not as user-friendly:

no SEPARATE delivery settings for manual mode and AUTO MODE

At this time with the MiniMed 670G, if you would like to interchange between Auto Mode and Manual Mode, you have to pay very careful attention to making sure you adjust the carb ratios and the active insulin time (AIT) under OPTIONS>DELIVERY SETTINGS>BOLUS ESTIMATE SETUP every time you toggle between the two modes. Since Auto Mode settings are more aggressive, this could spell disaster when one returns to manual mode from auto mode and forgets to dial back the carb ratio or the AIT. It would be great to see an option for separate delivery settings tailored for each mode in the next iteration of the pump. Since we know the AIT setting in manual mode has a completely different meaning as that on Auto Mode, it only makes sense to separate the settings.


I have written a lot on this topic and what I think causes it, but this is a major flaw that needs to be addressed by Medtronic. No only is it irritating but it a shame that this happens since the Guardian Sensor is a great improvement in terms of accuracy and stability over the Enlite Sensor. I personally think that it is time Medtronic started working on an improvement of the Contour next Link 2.4 meter, since I think the precision (or lack thereof) of this meter is at the heart of the “ENTER BG LOOP” flaw.

navigating the useR menu

Although the user interface is a big improvement in terms of aesthetics, navigating around the Medtronic Minimed 670G is not as easy as it was with the Medtronic Minimed 530G. My major issue is that it takes more than 2 or 3 buttons steps to get to the most basic of functions. For example, if you forget to calibrate the pump using the BOLUS or ENTER BG menu item, you have to browse through OPTIONS > UTILITIES> SENSOR SETTINGS>CALIBRATE SENSOR to be able to calibrate you sensor. A second example,  to change the basal or bolus settings, you have to browse to OPTIONS>DELIVERY SETTINGS

black box AND CONSERVATIVE nature of the auto mode settings

There is a lot that we do not know about the way Auto Mode works and the underlying algorithm. Probably it is a good thing not overload the user with too much information. But only being able to only control 2 or 3 settings in Auto Mode leaves the user feeling helpless especially when they know the suggested bolus by Auto Mode won’t get me to where I need to be. Granted that the FDA approved the closed loop pump on the basis that it was conservative enough not to plunge the user into an irreversible low, so I understand Medtronic’s hands were tied.

But the fact that it is not as easy to achieve the advertised target of 120 mg/dL means that insulin delivery is throttled well above this target. But a target of 150 mg/dL is easily achievable.

Talking about conservative, I have noticed that there is a larger discrepancy in sensor and meter BG readings especially with morning fasting numbers which in many cases put me close to 150 mg/dL while the sensor hovers around 120 mg/dL. Not sure about what is going on, but I get to wonder whether the predictive algorithm is weighted to be more conservative for certain times of the day.

It would also be nice for a user to see the basal rates being used in Auto Mode and the breakdown between the actual basal rate and the microbolus used by the pump to get to the target BG. I do not see why the user cannot use successful Auto Mode basal rates to tune Manual basal rates.

spike control not as easy on auto mode

Once again, due to the conservative nature of Auto Mode, spike control is not as effective as when you are in manual mode. It gets better as Auto Mode continues to learn but it is very had to achieve small spikes or even stay flat post meal time. I was able to do this with ease on manual mode.

Spike control is less effective because the pump stops dispensing basal/microbolus insulin for 15 minutes after one applies a bolus. According to Medtronic, this is done so that the algorithm can see the direction of BG readings after a bolus to avoid lows. But that in itself is counterproductive since it is taking the microbolus away from you when you need it most. Even if you wait for 15 minutes before eating as recommended, there is no way the basal/microbolus can catch up to the spike.

In most cases, with an aggressive carb ratio I am able to keep the spike below 180 mg/dL but I prefer not having to hit 140 mg/dL, which I am able to do on manual mode.

Notice Breakfast Spike and no micro-bolus/basal between 8:05 to 8:30. Also see the dip that occurred when I bolused for a second cup of tea with milk and then over-corrected for the low. Yikes.

I find myself more hesitant to eat high glycemic index foods on Auto Mode as compared to when I am in manual mode where I have honed in my basals over time to cover for spikes.

transmitter range

Sleep in the wrong position, then you will be woken up by the pump alerting you that the communication between the Guardian sensor transmitter and pump has been lost. This happened a lot for the Enlite Sensor too but it rarely happened for the Dexcom 5. There seems to be even a more dangerous flaw when the Guardian sensor loses communication with the pump while in Auto Mode. A couple times, I have slept through a lost sensor with no alert only to be woken up with an alert that the pump has exited Auto Mode.  The only way you realize that is was a lost sensor that caused the Auto Mode exit is by looking at the BG reading graph and you see a long blank period of no sensor BG signal.


For Manual Mode Basal Settings are Everything

Importance of Basal Settings

After nearly giving up on my pump, I found the very popular book by Gary Scheiner, Think Like a Pancreas: A Practical Guide to Managing Diabetes with Insulin. (Amazon) – I think this is a must-have book for people who want tight control of their glucose numbers.

At this point I had uncontrolled, severe hypoglycemia. With a new-born baby, this was not just a drag on my life but it was a bit dangerous. I do not know how many gallons of orange juice I drank to counter lows.

I had also not paid attention on the importance of fine tuning my basals. I was using a single basal which gave me big lows at night and when I was doing practically anything that needed me to expend a little energy.

Since many new pumpers are coming from a combination of short acting and long acting insulin injections, the idea of basals is a little foreign as compared to bolusing.

I think educators need to spend a little more time on talking about how basals are the foundation of successful pump therapy.

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