T Slim Tubing Question

Hi Everyone,

I started training on my T Slim yesterday and my trainer mentioned never to disconnect the tubing from the lock end as the insulin in the tubing could then be infused and overdose you. She said to always disconnect first from the inset. It seems straightforward but there are situations where this could happen which is worrisome.

I'm wondering this:

1- how much insulin is in the tubing at any given time?
2- how quickly could it be dosed if this were to happen?

I assume it's possible for this to happen:

1- by accident if you forget
2- by accident while you are sleeping or if the tubing/pump gets caught on something
3- by accident if you have an accident such as a car accident

In which case you not know it had happened and you may not be able to do anything about it possibly even if you did.

This doesn't seem very safe to me for this to be able to happen at all.

Were you all told the same thing when you trained?

The same thing can happen with any insulin pump that there is if damage occurs to the line. The amount of insulin in line will vary by how long line is and where the damage occurs.
Had my new kitten chew through the line about 8 inches from site. Was lucky did not go low and also that hindsight it before going high from no delivery later.
Disconnecting at the leur hub and then trying to reconnect will cause bubbles in line so be aware of than. Can happen if hub is not fully tightened.
As for my training there was no mention of this at all.

The lock does not come undone by itself. And there is no reason for you to ever unlock it. Just remove the tubing from your Inset insertion site if you need to disconnect.

If for some unknown reason the lock comes undone, I would just start a new cartridge and infusion set from scratch.

I don’t get it, why would disconnecting at the luer lock deliver insulin in the tubing? My understanding is that the reason not to do this is to avoid putting air bubbles into the line when you reconnect.

Hi 2hobbit1, I realized after I wrote this that it isn't a t-slim inset/ tubing- that is not good that this can happen with any type of tubing/pump I thought t slim was pretty much overdose proof but I guess due to the tubing issues it isn't- there is no tubing that would stop this from potentially happening? I'm not sure if I will feel safe at all now knowing this could happen even though she said it has never happened to her- she has type 1 and has used this pump for a long time.

I didn't even think of a kitten attack and I have been contemplating adopting a new kitten- I'm glad that you didn't go low at all, that is a good sign that at least if you realize it has happened then you're not going to be immediately infused with too much insulin but I guess 8" from the site would be less insulin also. My tubing is the shortest one, I can't remember the length but it looks like 1-2 ft.

Another thing I'm confused about is that we injected 120 units of saline into the cartridge. I'm using .3 basal per hour and I've only fake bolused 6 units so far but it is already down to 50 units.

I asked about this and my trainer said that it emptied quickly and went down to 80 units right away, I didn't notice that at the time, but I'm wondering where those 40 units went to?? Because although we practiced some bolus and other things we didn't do 40 units. So I'm guessing most of that is in the tubing? She said to put more into the cartridge next time if it empties too much but I thought the point was to put only a little more than I will need for 3 days when the next inset will be changed. I think she calculated around 30 units a day, more than I use, and added an extra day also.

Do you dilute your insulin? I remember you mentioning that and I'm wondering how you do that and how you figure out your bolus etc. then?

I don't get it either Niccolo, nor do I understand why they would all be designed with that possibility due to the danger. Maybe because that is the only way to assure continuous insulin flow? I don't know the physics of this, what happens to the liquid once it gets into the tubing and how it is released. But this is what she told me and she was emphatic never to do that otherwise this could happen. She works for tandem and she uses the pump herself so I assume she is correct. She said this has never happened to her so I don't think it's something that happens frequently obviously.

Hi Anthony,

Normally the lock will not come undone but as I and 2hobbit1 mentioned above there are situations where the tubing or the lock could be damaged and apparently this then allows the possibility of overdose. She has now told me to tighten the lock everyday when the pump is detached just to make sure.

I have figured out from the history that 93.9 units were loaded into the pump when we did it, I remember now there was an air bubble in the syringe and that may have wasted some units, I'm not sure, but one unit is a tiny amount so that seems possible. The cartridge was filled with 75 units, the tubing was filled with 18.6 units and the cannula was filled with .30 units, so I'm guessing my tubing will normally have 18.6 units at any given time, that would definitely be a disaster if all of it were ever released so I think I will ask about diluting the insulin also.

Hi meee,

If I understand what you are asking, I don’t believe this is a real problem. There is no way that disconnecting and then reconnecting could suddenly infuse all the insulin in the line (about 16 units total if you are using the 23" shortest version). The physics require pressure to be exerted and you would not get that just from disconnecting and reconnecting at the Luer lock. I do not see other situations like car crashes etc causing it and think if you were in a car crash, there are likely bigger concerns.

I started on the tslim recently myself. I am an engineer and physicist by training and admire the science that has gone into the design. I do not see cases where overdose is going to be caused. Under-dosing (due to kitten attacks or whatever) is a lot more likely - blockages, infusion sites not working etc are a lot more likely. I suspect your CDE told you not to disconnect the Luer lock because it would easy to forget to reattach and because of the possibility for contamination.

Best of luck!

Thanks chipchap,

She was very emphatic about not doing this because it could cause overdose, there is no mistake about this. I'm sure she must have a reason for believing this- she didn't say anything about air bubbles with regards to the luer lock being disconnected as I recall, but I have no intention of disconnecting it when the pump is attached to me or unless I'm changing the inset etc. which I have to go do right now. I will have to ask my endo about this because I'm worried now about going on insulin on Tuesday without it being diluted. My pump history said 18.6 units and I know that dose could easily be fatal for me- I do have the 23 " one I believe.

Can you explain the physics of this? I'm interested to know what will happen if it is damaged or detached. I have found in life we always say this can never happen, and then it does, lol.

I updated this on my other question about refilling the cartridge, but I want to mention it here also in case anyone is interested. I spoke with a tandem customer service rep to get help refilling the cartridge and he said the only way something like this could happen would be if you were in a pressurized situation like the cabin of a private plane(not sure why it has to be a private plane? I guess because that situation wouldn't happen on a public plane), lying down, with your tubing and pump above your head like an iv and then it would take about 30 minutes for the fluid to go into you. So if he is correct, there is no need to worry about this happening for most of us. I plan to test it out with the inset in an orange. Or maybe when I remove the next inset with saline.

Disconnecting at the luer lock does put air bubbles into the tubing. This is also why doing this delivers insulin. Air takes up space. If you put air in an already full length of tubing, it has to push insulin out the other end to make room. Next time you change out your cartridge and tubing, try disconnecting the luer lock (after everything is disconnected from you, of course) and see what happens.

It's not really an issue though, since there's not really any need to disconnect there. If you tighten it correctly it should stay together just fine, and when you need to disconnect you just do it at the set.

Thanks Olivia,

My trainer told me to tighten the lock daily also.

I did an experiment.. first when I disconnected the luer lock on a detached tubing/ set some saline came out the luer lock end. But when I connected an old set,cartridge etc. to a new inset in a tomato and undid the luer lock while attached nothing came out the luer lock end until I also detached the tubing from the tomato. I don't know if any saline actually went into the tomato, it didn't look like it did and I saw no air bubbles in the tubing in either situation. According to one rep I spoke with at Tandem however, no insulin will be dosed is the luer lock is detached or the tubing damaged etc. unless those circumstances I described below also happen. Another rep also told me that there is 1 unit of insulin per 3 inches of tubing. So at any given time, my tubing- 23" will have about 8 units in it. Still a big dose for me but if I realized it had happened probably not fatal.

Forgot to mention that it would be an issue if it does actually dose insulin in that situation( without being in a pressurized setting with the pump and tubing raised above you), for the reasons I mentioned in my post: unintentional or accidental disconnection of the luer lock and or damage to the tubing, which could then theoretically cause insulin dosing without you maybe even realizing what had happened.

Paul, I spoke with a rep who said there is 1 unit of insulin per 3 inches tubing so the 23" has only 8 units apparently. Hopefully this will never be a problem due to the special conditions apparently needed for any of this to happen.