How does it work? How can it help?
The Medtronic 670G needs 3 key parts to function; a continuous glucose monitor (CGM) with a sensor, an insulin pump, and a special algorithm imbedded in the pump called the PID-IFP algorithm (this is what makes it special).
The CGM works similarly to the CGMs that I described in my previous posts. It is minimally invasive, and reads the users glucose levels every 5 minutes (see previous post for more details on CGMs). These glucose readings can be viewed in real-time on the user’s insulin pump.
The 670G functions in two different modes; manual mode and auto mode. When the user is in manual mode, the 670G functions similarly to other sensor-augmented pump therapies and uses basal and bolus settings inputted by the user and their clinician. Auto mode (aka hybrid closed-loop-mode) uses the special PID-IFP algorithm to continuously modify the amount of insulin given by the pump through a “micro-bolus” (a small spurt of insulin). This micro-bolus is recalculated by the algorithm every 5 minutes, is dependent on the user’s sensor readings, and replaces the pump’s basal feature while in auto mode. This algorithm targets a BG of 120mg/dl (can be adjusted to 150mg/dl during exercise) and adjustments are made based on several factors including; insulin on board (IOB), sensor rate of change, time away from target, and total daily dose (TDD).
The algorithm readjusts its settings every night at midnight and considers the previous 6 days of data. It is therefore continuously learning the user. For instance, if the user’s BGs are consistently elevated, it will increase their TDD of insulin. This, in turn, will increase the max basal rate calculated by the algorithm allowing for more insulin to be given in micro-boluses. Although this is beneficial long term, the algorithm does not account for quick changes in BG averages such as during sick days or during menstruation (because it works from the 6-day average). It also cannot account for patterns such as dawn phenomenon (don’t worry, there are tricks for this-talk to your clinician/CDE for help).
It is important to remember that as with other pumps (or manual mode in this pump), the user still needs to input their carbs into the bolus calculator. Auto mode uses the same carb setting for the bolus calculator in auto mode as it does in manual mode. You and your clinician will need to work together to come up with your appropriate carb factor. Correction boluses are calculated by the algorithm and target the correction to a BG of 150mg/dl. The algorithm then continues to use the micro-bolus feature to correct the BG to the 120mg/dl target.
Let’s talk about safety.
In addition to the safety features already embedded into the algorithm, the 670G includes the “suspend on low” and “suspend before low” features. These can be used in both auto mode and manual mode. In manual mode they must be turned on, but in auto mode they are included in the algorithm. These features will suspend basal or micro-bolus delivery when the sensor glucose reaches a preset target (suspend on low) or when the sensor glucose is predicted to reach that target within 30 minutes (suspend before low). Clinical trials have shown auto mode to be very safe with increased time in range (70-180mg/dl) and decreased hypoglycemia (<70mg/dl). Many of the patients I have seen in auto mode spend <1% of time in hypoglycemia!
On a personal note, the 670G has been dreamy for me. I have always had very good control. Before starting the Medtronic 670G my HbA1c level was 5.8%. I had pretty steady BGs, and liked to run them between 70-100mg/dl as often as I could. I have always been more afraid of the highs than the lows because I worry about complications. I probably had a low ~1-2x/week. Trying to keep my BGs low, but not too low was hard!
When I first started 670G I was frustrated because my BGs were always in the mid 100’s, which was WAY too high for my comfort. There were many times that I wanted to stop auto-mode so that I could have my 80’s and 90’s back.
After 3 months I retested my HbA1c and it was 6.4%. I was thrilled! Not only was my HbA1c still at goal, but I was not having ANY lows.
The 670G has given me a lot of things back. I have had diabetes for basically my whole life and didn’t even realize how frequently I was thinking about my BGs, making small pump adjustments, or eating little snacks to try and avoid my hypos (I’m a micromanaging diabetic). This is the first time since I can remember that I have been able to sleep through the night. I can now exercise, clean my house, and go dirt biking without fear of low BGs. Just last week I tested my HbA1c again and it was down to 5.7%. Even better than before the 670G!!!
It was an adjustment period and it took me a while to let go of control, but this pump has done wonders for me and I hope that all of you get the chance to try it!
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