Medtronic’s Hybrid Closed Loop System: Getting More Bang For Your Buck
By, Gary Scheiner MS, CDE, Jennifer Smith RD, LD, CDE, Alicia Downs RN, MSN, CDE, Annette Valle RN, CDE
It’s been about a year and a half since we started using and training/managing patients on the Medtronic 670G “hybrid closed loop” system. And we’ve learned a lot. We’ve learned that 670G is beneficial for some, but it clearly isn’t for everybody. Yes, for the “average” person with diabetes, it can produce improvements in glucose control while helping reduce the risk of dangerous hypoglycemia. But there are limits to the degree of glucose control that can be achieved, and there are many hassles and extra tasks involved with using the system.
There are other hybrid closed loop systems that are already in use, despite not being on the “FDA approved” list of systems.
- Loop and OpenAPS systems are highly effective for improving glucose control, but they require special equipment and an “app build” to get them up and running.
- Tandem’s T:Slim with Basal IQ is easy-as-pie to use, but it only turns off basal insulin to help prevent lows.
- Other systems are coming to market soon: Tandem’s Control IQ, OmniPod’s Horizon, Tidepool Loop and BigFoot Biomedical’s system are all slated to make automated basal adjustments (similar to Medtronic’s 670G, but with less work on the part of the user), but until the pre-launch studies are completed and the FDA signs off, all we can do is picture them in our daytime fantasies.
So for those who want 24-hour automated basal adjustment NOW that is FDA approved, that really leaves just one option: 670G.
Medtronic has taking steps to cut down on some of the quality-of-life drawbacks, such as requests for repeated calibrations, with a new-and-improved transmitter. Still, there are a host of other downsides that don’t look like they’ll be going away any time soon.
The question then is this:
How can we squeeze better performance out of the 670G Hybrid Closed Loop System?
I think most of us would be willing to put up with the little inconveniences if it means much better glucose control, not just a slight improvement in time in-range.
To answer this question, the clinical staff at Integrated Diabetes Services put its collective brains together and came up with the following suggestions:
- Get your settings right BEFORE starting auto mode (AM).
True, when you’re in auto mode, the system doesn’t give a damn about what your basal settings were before. It flattens everything out and adjusts based on the situation. But you’re not always going to be in auto mode, and you don’t want your control to suffer when you’re in “manual” mode. That means getting your basal rates to hold you steady when you’re in a fasting, non-bolused, not-exercising state. Also, setting the carb ratios so that you’re back close to your target BG 3-4 hours after eating, and knowing how long your boluses truly last – something that can best be determined by analyzing CGM data following a correction bolus.
Carb Ratios and Active Insulin Time are the only parameters that are carried over directly from manual mode to AutoMode (AM), so it makes sense to have these setting dialed in before starting AM.
Having incorrect settings when you start AM can produce a rocky start for the first few days/weeks. Yes, AM will make adjustments to basal delivery to help flatten things out, but these adjustments are temporary and subtle, so don’t expect them to solve everything.
- Understand how AM operates.
AM updates its algorithm (the formulas used to determine basal adjustments and correction doses) at midnight every night based on your insulin usage for the previous six days. For this reason, it is best to use the pump in MANUAL mode for a full six days before starting to use AM.
Because AM adjusts its algorithm based on the last six days of insulin use, be careful following periods of sharply increased insulin requirements, such as illness, steroid use, binge eating or prolonged stress. AM may be more aggressive than usual following these periods, so consider using the temp target (150) for at least a few days following temporary periods of increased insulin use.
When in AM, the only two settings that are “carried over” from manual mode are your carb ratios and active insulin time. AM doesn’t use your current usual basal rates or your correction/sensitivity factor. Automode uses a target of 120 mg/dl (unless you are using the “temp target” feature), and will only suggest correction boluses if your glucose is above 150. Likewise, it will only recommend a reverse correction (deduct from a meal dose) if your glucose is below 100.
There are limits to how much AM will increase basal insulin. This varies from person to person. Based on our experience, it seems to be roughly 2.5 times your “average” basal rate. So AM will not be able to fix high readings quickly; use correction boluses instead. Likewise, AM will not be able to “fix” lows once they have already occurred. Reducing or turning off basal will produce a gradual glucose rise starting an hour or two later. Lows (or near-lows) still need to be treated with rapid-acting carbohydrate.
- Do all you can to ensure consistent insulin absorption. Problems with insulin action or delivery will interfere with AM’s ability to regulate your blood sugar levels.
- Change your infusion set frequently – every 2-3 days
- Rotate your sites properly (avoid using the same spot twice in a month)
- Change your infusion set at the first sign of site irritation or ineffectiveness
- Store your insulin properly and avoid using past the expiration date
- Remove air bubbles from your reservoir and tubing before using them
- Know when to take yourself OUT of auto mode.
There are situations when auto mode has the potential to… shall we say… get in the way of optimal glucose control. For example:
- When consuming a slowly-digesting meal, a normal bolus may peak and finish working too early. Because the extended (square/dual) bolus feature is is not available when using AM, it might be best to temporarily switch to manual mode and bolus using a square or dual delivery. b. Temporary basal
- Switching out of auto mode allows you to set temporary basal rates for situations such as sick days, stress, prolonged exercise, alcohol consumption, and high-fat meals.
- Steroids, such as cortisone or prednisone, can raise your blood sugar significantly for several days. AM may not be able to keep up with the increased insulin need. Switching to manual mode with a temp basal increase or a secondary basal pattern tends to work better.
- On days with intense or prolonged physical activity, both basal and bolus insulin needs can be markedly reduced. AM limits the length of time at which very low basal delivery is permitted, and bolus doses calculated while in AM will likely be too high when exercising.
- If you have elevated blood sugar due to an infusion site issue, it is best to switch to Manual Mode, change out your infusion set, and deliver a bolus via injection to correct the high BG. Once the BG is back in-range, switch back to AM.
*Oh, by the way: Don’t forget to reactivate “suspend before low” when turning AM off, as this feature is deactivated every time AM is turned on.
- Don’t hide things from AM.
When disconnected, put your pump into suspend so that the system knows you’re not receiving any insulin. If the system thinks you’re receiving AM-driven basal insulin when you’re actually not, it will tend to under-dose you for elevated or rising blood sugars for the next several hours. Likewise, if you give yourself an injection of insulin or use inhaled insulin (Afrezza), turn off AM for the next 2-4 hours. Otherwise, the system may over-deliver insulin, thinking that you have less insulin-on-board (active insulin) than you really have.
If you eat, enter the carbs and bolus accordingly. AM is not designed to “cover” most meals and snacks. Small, slowly-digesting snacks may be an exception.
And do not, under any circumstances, enter a glucose value (for a bolus calculation or correction) that is not true a true value based on meter or CGM data. Doing so may cause AM to alter your insulin delivery patterns for several hours, and the discrepancy between the glucose entry and the sensor value may force you to perform extra calibrations.
Some people prefer to enter “ghost carbs” (carbs that they didn’t actually eat) in order to get the pump to deliver a bolus to correct elevated readings. While this practice is certainly better than entering a fictitious blood sugar value, it is generally discouraged because of the effect it will have on AM for the next several hours.
- Get your sensor to work as well as possible.
AM (and your peace of mind) depend on reliable sensor data. Calibrate your sensor three to four times every day, ideally when glucose levels are steady in order to avoid discrepancies related to lag time. Use the Contour Next meter that came with your pump if at all possible. This is the most accurate meter on the market, and will provide the truest readings for calibration purposes.
Follow the correct procedures for inserting your sensor, including all of the taping procedures. A secure/stable sensor will perform better than one that is often peeling loose.
Whenever there is a significant discrepancy between the sensor and calibration values, you may be asked to calibrate again right away. DON’T DO IT. Wait at least 30 minutes so that the values will match more closely. This can help you to avoid a sensor error or AM failure.
- Plan ahead for exercise. WAY ahead.
Don’t forget that rapid-acting insulin typically takes 3-4 hours to clear. Basal adjustments made by AM a few hours ago are still affecting your blood sugar. If exercise tends to make your blood sugar drop, set the temporary target (150) at least an hour before starting exercise. Keep the temp target running after exercise if you tend to drop following your workouts.
If the 150 target is not enough to prevent a low blood sugar, consider consuming rapid-acting carbs prior to the workout without bolusing. And as mentioned previously, if you disconnect from your pump during exercise, place the pump into suspend mode.
- Re-think the way you treat hypos
When glucose levels are approaching a low level, AM will usually reduce basal insulin significantly. This reduction may continue until the glucose levels returns to a safe level. As a result, treatment for a low or pending low will require LESS carbohydrate. The combination of your usual carb treatment and reduced basal may result in a rebound high blood sugar.
Also, be careful about “trusting” your sensor when recovering from a low. In many instances, the sensor will take 30 minutes or more to detect the blood sugar rise after you have treated. If you trust the sensor under these conditions, you will over-treat. Best to check your glucose with a fingerstick 10-15 minutes after treating the low in order to verify that your blood sugar has (or has not) risen to a safe level.
- Pump setting adjustments
Switching into AM may require some adjustments to your usual pump settings. IF your pump’s settings were not fine-tuned prior to using AM, you are likely to find that your carb ratios were too conservative and your pump’s usual basal settings were too aggressive. If you make changes to your carb ratios after examining your data from AM, consider adjusting your pump’s basal settings at those times as well. That way, your glucose will be less likely to go high or low when revering back to manual mode.
Although rapid insulin is known to have an active time of about 3-5 hours, it can be helpful to set a shorter time (2 to 2.5 hours) when in AM. This causes AM to consider less “active” insulin when calculating correction doses. This can be helpful to those looking to make the algorithm more aggressive.
- Avoid grazing!
Eating and bolusing too frequently can get in the way of optimal system performance. AM permits more aggressive basal adjustments when there is little-to-no active bolus insulin present. Grazing makes the system less aggressive and leads to more AM “kick-outs” due to prolonged maximum or minimum basal delivery.
- Analyze your data
If a tree falls and nobody hears it, does it make a sound? If your blood sugar is chronically out-of-range and nobody does anything about it, what good is it? Download your pump and look at your data regularly; weekly at the beginning and monthly after things settle down.
Carelink is Medtronic’s designated data software. It can be a bit confusing and doesn’t offer all features we want (no sensor overlay report, for example), but it does provide some useful insights. In particular, check the Meal Bolus Wizard report to see if your carb ratios are in need of adjustment, or if you need to bolus earlier (spikes right after eating are usually a sign of bolusing too late). Physical activity and other lifestyle events don’t show up in Carelink, so keep track of these on your own, and see how your glucose responded in the Weekly Review Report.
Another option for reviewing/analyzing your data is a web-based program called Tidepool. Unlike Carelink, Tidepool allows notes to be taken and uploaded into the reports. It also allows you to actually SEE what the basal rate was when AM was ticking it up and down throughout the day, and individual day reports are magnified for easier interpretation.
So what can realistically be accomplished with 670G?
The pivotal trials completed by Medtronic a few years ago showed that users of 670G achieved an average A1c of approximately 6.9% (avg glucose of about 150 mg/dl) with about 70% of time in the 70-180 range.
The patients we have worked with who apply the strategies described above have managed to achieve the following:
- Average blood sugars from 130-145. Lower averages are not realistic with current target setting and correction parameters in AM. Users who are used to using lower targets should set their manual mode target to 120 before starting to use AM in order to become accustomed to the pending changes. This corresponds to an average A1c of 6.5%.
- Time in-range (70-180) approximately 80-90% of the time.
- Fewer than three hypoglycemic events per week.
Not too shabby!
The idea here is not to sell you on any particular product. We’re proud of the fact that we give our patients a fair rundown on everything available so that they can make an educated choice. But if you already have the Medtronic 670G or are giving it strong consideration, hopefully these suggestions will help you glean the most possible value from it.
Feel free to reach out to our team for additional guidance. We are happy to work with anyone via phone and the internet to help get the best possible results from any system.
Meet the Authors!
Gary Scheiner MS, CDE
Jennifer Smith, RD, LD, CDE
Alicia Downs RN, MSN, CDE
Annette Valle, RN, BSN, CDE
If before 670G AM we tend to use higher basal (doing the bolus work) and 670 learned this, after we tried for some weeks AM and Glucose is tend to higher (180-200) is better to turn off AM, reduce manual basals, work with RC (the one that we will use in AM), and let the 670 to learn again about tendencies and manual analytic?
also and then turn on AM again, but with the new analytic learned from previous basal, RC, and sensibility changes?
to be clear, no system currently FDA approved “Learns” our basal needs. they all simply react to cgm trends. The system can’t “learn” for example that I need more insulin between 3 and 6 am based on previous days.
nothing that smart just yet, except people :)
the system does not “learn” anything about basal patterns. it simply reacts to the CGM data trends and increases or decreases insulin to achieve target ranges.
I have been using the 670G for 3+ weeks now and since I started every Meal Bolus more than 5g of carbs causes background insulin to go to zero for 2-3 hours. Is this normal for everyone? After a meal, I am sometimes as high as 308 and have always had very aggressive carb ratios, way more than all pumps like, but still I do not recover from a meal until 5 hours later. When the background insulin resumes 2 hours later it takes 3 more hours to get me close to 120.
HI Larry, the 670G Automode system always reduced or stops basal following a bolus to estimate the impact and how to respond (all part of Medtronic’s “proprietary algorithm” but it is clearly staying off for far too long. it sounds like your sensitivity probably needs some adjustment. We work with our clients to help them get settings and use patterns dialed into make the most of their systems and work around the more limiting features.
Hi. Great article. Do you know if AUTOMODE recalculates based on BOTH the auto mode settings AND the manual mode settings?? eg if the person is running high so you exit to manual mode to give a bigger bolus in manual mode (as manual mode aims for eg 6, but auto mode only corrects to 8.3). so does the LEARNING part of AUTOMODE take into account – OK a high manual bolus, so I will LEARN from this and give more insulin in the next few days?? or is the manual bolus lost for auto mode, so that giving a manual higher bolus negatively impacts the auto mode learning?????
automode does not learn patterns to behaviors the ONLY pattern that it learns is our average total daily dose of insulin, it is not as “smart” as many have been lead to believe.
it has multiple safety checks but does not “learn” from our daily highs lows or treatments at all. the only settings used in automode are the duration of insulin action time and carb ratio.
Thank you for the article. Is there any successful way to get auto mode to adjust for the dawn phenomenon?
The auto mode has a target that is to high for me. The current target raises my A1c and makes my blood glucose higher than normal. Makes me feel horrible. Is there a way to adjust for this? The target is unchangeable from what I’ve been told, so if I calibrate my sensor 20 higher than my actual blood Glucose meter readings will that lower the target if I wish to bring the target down by 20?
I need the auto mode to not be always raising my blood glucose so high. I had a 5.4 A1c before and was stable with blood glucose levels around 80-90, but the 670 is keeping my levels always over 120. I worried it is damaging my body. It’s the worst I’ve felt in years. If I can lower the target and adjust to get it to treat the dawn phenomenon it would significantly help.
Can you recommend any suggestions?
Hi Matt, the 670G system is only capable of keeping an A1C in the low 6s at its absolute best. Clibrating the sensor higher than actual blood sugar has not been shown to be a great way to overcome this because it increases the number of sensor alerts and failures, which are the biggest struggle with this system to begin with.
The A1Cs that the 670G maintain are in a range that would not indicate an increase in risk for long term complications. HOwever your personal goals are not compatabile with what the system is able to do. you would likely find your best control to use the smart guard features to suspend before low and reduce hypoglycemia, but otherwise work in manual mode.
Excellent article – thanks. I’m a 670G user for the last year & Minimed pumper for about 3 decades. I had a bad high BG/sick day recently due to a bent canula. I made the mistake of correcting multiple times for the high BGs rather than changing the infusion set sooner. I got back in range only after a large correction with an injection and I changed the infusion set to find the canula bent 90 degrees – no insulin delivered with that set. I should have learned by now not to try to avoid wasting an infusion set when BGs are not responsding normally to insulin.
re: 5. Don’t hide things from AM. You discourage “ghost carbs” and fictitious BGs – what about ghost “fill canula”. I’ve done this to simulate a manual bolus to correct for high BG (without changing active insulin) when I expect the AM algorithm will not correct aggressively enough.
I can see that fictitious BGs used only for corrections would be problematic for AM, but as you stated “…Lower averages are not realistic with current target setting”. I would think that if you wanted a lower target (but aren’t up for the challenges involved with Loop and OpenAPS) you could consistently manually enter calibrations and other BGs 10mg/dl less (or perhaps better 10% less) than the reading on the Contour Next meter.
the problem we find here, is that inaccurate BG entries are likely to trigger more safety alerts from the CGM and eventually cause CGM error/failures
Canula fills are a double sided sword,
we can get more insulin, but then when our BG drops the system is just going to reduce basal, and we also now have essentially a bolus without IOB calculation which increases risks of stacking and causing inadvertant lows.
Has anbody had a bent canula? How did you handle it?
bent canulas are , unfortunately, part of life pumping.
making sure you’re using the right set is key. too long a canula increases risk of bent canulas. also making sure you have the right angle of insertion for the set, and that you’re not getting too close to underlying muscle fascia all reduce risks of bent or crimped canulas.
That’s unfortunate news for me and my endocronologist. I’ve traditionally had A1C between 5.5 and 6.25.
My other issue with the 670G is the seemingly useless alerts. Dropping me out of auto-mode in the middle of the night just because my BG has been stable at 100 for more than 2.5 hours seems silly. It was a nightly occurrence for several weeks before I started eating before bedtime to raise my BG. I guess the 670G doesn’t like to be idle.
I have no idea how to interpret the bazillions graphs that are available in the Carelink system.
I think the avoid grazing advice is challenging. If I’m hanging out with a group of friends drinking a few craft ales, I am going to be testing and bolusing for each 8oz pour. Is that to be avoided?
My favourite form of exercise is hiking. I have not found a safe way to do this while in auto-mode. I have learned to disable all Insulin delivery during hikes and I must admit I’m afraid to do a you sort of weight training or HIT due to the fear of hypoglycemia. It seems ridiculous to consume sugary things while exercising.
Khurt, we work with our patients to find the right ways to use (and at times not use) automode effectively for activities, exercise, foods etc. This helps reduce the burden of the system and get as close to desired results as possible.
Thank you for this very helpful article, I have been struggling to get a good control on my 670G. After reading this you answered many questions that I had.
our pleasure Ruben! I encourage oyu to subscribe to our newsletter where we send out great info monthly.
Also you can give us a call to set up an appointment for more advanced and individualized use education.
Any suggestions for diabetics with Gastroparesis? I feel that I may not be a candidate for AM due to it.
Great read for those that are in AM though.
Automode is really difficult for patients with GP. We have a couple who have made it work, but the inability to extend boluses can be problematic. split bolusing can help somewhat, but has its own draw backs too. If you are interested in hybrid closed loop technology you may want to look into LOOP. This DIY hybrid closed loop allows us to tailor our digestion time, and therefore improve how the system responds.
Hi my name is Carol. I have a problem with my blooo sugars going low at about 3-4 AM. My sensitivity factor is 50% and my carb ratio is 10. What to do? Please help me.
We would need to work with you as a patient to be able to advise on how to take your insulin appropriately. Please call our office to schedule an appointment with one of our educators.
This is a good review of the 670G and how to have success with it. I have been on the 670G for 20 months now. I was one of the first 10 people in the nation and the first person in the Philadelphia region to get the 670G when they started shipping. I have had great success. I am in AM 99% of the time and am consistently in range 80% to 90% every month. Before the 670G I had frequent lows, sometimes multiple in a day. I now most often only have 2 to 3 a month and some months none. I was trained by my local Medtronic Clinical Manager and I always stress that I believe proper training is important to having success with the 670G.
Gary, I have read several of your books and follow your web site.Enjoy your books and hope you write more of them. I’ve been on the 670 for about 19 months, so track everything you write on it. In your latest write up, you mention the aggressive CR ratios. I was hoping to see a comment on what to expect for a basal/bolus % for AM using the 670. With the 630, I was around 50/50. With the 670, it varies, but is around 39/61 because of my aggressive CR. Was wondering if one should be concerned or is this what to expect? If yes, how would one work their way back toward 50/50? If not, writings suggest higher boluse lead to less absorption and other issues, so should those issues be a concern? Thanks again for everything you do for the diabetic community. Thank you.
Typically in consistent high levels of automode use we see an increase in basal insulin use, largely because rather than bolusing for corrections, automode is increasing basal to compensate. The big exception is when users are more prone to low blood sugars. In this case automode is consistently reducing basal delivery for extended periods to reduce hypoglycemia. So it really depends on whether the user’s settings were effective before automode start (Very often basal insulin settings are too high and basal is actually doing part of the job of the bolus insulin at meal times) which way we are going to see them shift after starting automode.
Also users that bounce in and out of automode see higher bolus insulin use due to exiting automode and correcting issues.