Closed loop system

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Tom1982

Tom1982

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Sure I’ve spoke about this before, but everyone at home is full of colds and coughs and so I’m stuck at home bored! I’m trying to figure out the basics of a closed loop system. Does the pump react to the info from the CGM and deliver insulin accordingly?
 
Hi Tom
You have got the basics of it.

For the Basal insulin the pump learns what you need. It requires a 48 hour warm up when you first use the pump during which time you use it in manual with a basal rate you have set up. After this you can use it in closed loop. In closed loop the pump check your sensor glucose every 5 minutes and makes adjustments to your basal rate where necessary, and so on throughout the 24 hours.

The bolus is the same as with any pump, tell it the carbs and the pump works out the insulin needed for that, taking account of active insulin/insulin on board,along with the current sensor glucose level. There is no option of different types of boluses as they are not needed. The looping system makes adjustments if you have made a bit of an error in carbs or need an extended bolus. For example, if I eat a very fatty meal, I know the glucose will not be released all at once. I bolus for a bit less than I have calculated and then let the loop deal with the later glucose. Not perfect but a lot easier for me in the evening. I might go to bed a bit higher than I would normally but I know that the pump will deal with it whilst I sleep. My graph has a bit of a wobble but the lumps reduce and flatten out by the early morning (unless Inhave it horribly wrong!!)

I find that it needs a bit of help if I am doing prolonged exercise and also if I overestimate the carbs a lot, or forget to eat after pre-bolusing.

Happy to answer any questions.
 
SB2015 said:
Hi Tom
You have got the basics of it.

For the Basal insulin the pump learns what you need. It requires a 48 hour warm up when you first use the pump during which time you use it in manual with a basal rate you have set up. After this you can use it in closed loop. In closed loop the pump check your sensor glucose every 5 minutes and makes adjustments to your basal rate where necessary, and so on throughout the 24 hours.

The bolus is the same as with any pump, tell it the carbs and the pump works out the insulin needed for that, taking account of active insulin/insulin on board,along with the current sensor glucose level. There is no option of different types of boluses as they are not needed. The looping system makes adjustments if you have made a bit of an error in carbs or need an extended bolus. For example, if I eat a very fatty meal, I know the glucose will not be released all at once. I bolus for a bit less than I have calculated and then let the loop deal with the later glucose. Not perfect but a lot easier for me in the evening. I might go to bed a bit higher than I would normally but I know that the pump will deal with it whilst I sleep. My graph has a bit of a wobble but the lumps reduce and flatten out by the early morning (unless Inhave it horribly wrong!!)

I find that it needs a bit of help if I am doing prolonged exercise and also if I overestimate the carbs a lot, or forget to eat after pre-bolusing.

Happy to answer any questions.
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That’s great. It really seems like the way to go, What exactly is the function of the Basal dose? Is it to keep you ticking over at an in range level? Or are there additional purposes?
 
The Basal is supposed to keep BG stable in the absence of bolus.
 
That's what they are working on to make fully closed loop systems. Based on how my daughter's works though, I don’t think it would be able to react quickly enough to cover a large bolus dose and you’d spike really high and then it would struggle to get it down again.
 
Sally71 said:
That's what they are working on to make fully closed loop systems. Based on how my daughter's works though, I don’t think it would be able to react quickly enough to cover a large bolus dose and you’d spike really high and then it would struggle to get it down again.
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Ah right, so the manual bit for the bolus is just to help it know that a big in rush of carbs is coming?
 
Tom1982 said:
Ah right, so the manual bit for the bolus is just to help it know that a big in rush of carbs is coming?
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Exactly that, yes. So a bit of manual tweaking let's you lower the peak. I think one of them has simplified bolus (so you say "small", "medium", or "large" rather than a real carb count), but I guess there's some value in keeping in practice with prior carb counting for when you need to do it.
 
Tom1982 said:
That’s great. It really seems like the way to go, What exactly is the function of the Basal dose? Is it to keep you ticking over at an in range level? Or are there additional purposes?
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Basal insulin is to deal with the output of glucose released by the liver. In MDI it is a once or twice a day slow release insulin but this can be quite a numb tool to do a very intricate job. A properly working pancreas doesn't have 2 different types of insulin like a basal/bolus regime, it just secretes small amounts of fast acting insulin all the time to deal with the liver output and larger amounts to deal with food and these amounts are balanced by the liver and pancreas communicating. A pump is a much closer approximation to the way a healthy pancreas works. It only used fast acting insulin and provides a steady trickle of that every few minutes to cover your basal needs and then you tell it how many carbs you are going to eat for it to give you a big extra chunk to cover food.
The liver releases glucose at different rates throughout the day and night depending upon what your body needs, so you will likely need a lot less insulin at 2am in the depths of a deep sleep but more on a morning as you wake up (Dawn Phenomena) and less when you exercise or afterwards, so there will be times when you have too much basal insulin and other times when perhaps you don't have enough with MDI, but with a pump you can adjust it to what your body needs hour by hour and if you decide to go for a long hike, you can put on a temporary basal setting, so that it only delivers say 50% of your normal dose, to account for the exercise, or if you are going hypo, you can suspend your basal dose completely with a pump until your levels are back to normal. It is kind of like the difference between buying a suit off the peg and having it tailored to exactly fit your body. That is kid of the basics of it. Add in a CGM to form a closed loop and you don't need to tell it to suspend your basal when you are going low or increase your basal when your levels go too high, it makes these adjustments itself.... most of the time, but as with anything, you have to be alert to it working correctly and be prepared to intervene if things go wrong, so having a good understanding of the basics is helpful if not essential before using such a system as they are not completely fool proof and you do still have to carb count of course.
 
So this is probably a really stupid thing to ask but why isn’t there a pump with say, 1x vial of insulin and 1x vial of glucose, tiny little separate delivery tubes and an integrated CGM? job done!?
 
Tom1982 said:
So this is probably a really stupid thing to ask but why isn’t there a pump with say, 1x vial of insulin and 1x vial of glucose, tiny little separate delivery tubes and an integrated CGM? job done!?
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I think CGM sensors and pump cannulas need replacing with different frequencies (so couldn't be combined just for that reason).

There exist (experimental) dual pump systems, but they're more complex and expensive. I think they use insulin and glucagon and there's a difficulty in making glucagon last long enough to be practical (though I think there's been some progress with that).

Overall, though, my sense is that single pump closed loop systems are such an advance that adding an extra pump might just not be worth it.
 
Tom1982 said:
So this is probably a really stupid thing to ask but why isn’t there a pump with say, 1x vial of insulin and 1x vial of glucose, tiny little separate delivery tubes and an integrated CGM? job done!?
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I presume manufacturers are being encouraged to produce lower cost systems so more of us can be offered one. It looks like Libre 3 might be an important part of that. (Likely one hormone (and pump) rather than two, though.)
 
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I believe size would be another reason.
Not everyone is as fussy as me but a normal pump has a minimum size for electronics, battery and insulin. Adding glucose/glucagon would make it bigger. Especially for a small child.
 
Bruce Stephens said:
I presume manufacturers are being urged to produce lower cost systems so more of us can be offered one. It looks like Libre 3 might be an important part of that. (Likely one hormone (and pump) rather than two, though.)
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Ah I see. So is there a reason people stay on pens?
 
helli said:
I believe size would be another reason.
Not everyone is as fussy as me but a normal pump has a minimum size for electronics, battery and insulin. Adding glucose/glucagon would make it bigger. Especially for a small child.
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So what I’m after is a closed loop system with the smallest thinnest patch pump possible. Don’t care what it costs! But our team or whatever they are called, just seem to switch off and continue to offer us the old kak they’ve got. What is the best one about?
 
Tom1982 said:
Ah I see. So is there a reason people stay on pens?
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Some people prefer the old-school way and funding is quite hard to get if you don’t meet the NICE funding criteria - it’s a lot easier to get funding for children under 12 as the guidelines are different
 
Tom1982 said:
So what I’m after is a closed loop system with the smallest thinnest patch pump possible. Don’t care what it costs! But our team or whatever they are called, just seem to switch off and continue to offer us the old kak they’ve got. What is the best one about?
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We use the Tandem T-Slim with Dexcom G6 and have only recently upgraded to hybrid closed loop software, and it's pretty good. We certainly get a lot less alarms from the sensor. You have to remember that insulin takes up space and you don’t want to be doing refills every day so there's a limit to how small the pumps can get. Also, with a child under 6 years old their insulin doses might be too small for the system to make effective adjustments so you may well not be able to do looping yet anyway. No reason why you couldn’t have a pump though and use it without integrated sensors and then upgrade when appropriate.
 
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