I’ve only been pumping for a month and this has been bugging me since I started. I’d ask the CDE who trained me, but I’m not certain she’d really understand what I’m asking and would just tell me to complete all the steps for a set change. So here’s the question: when I change the site and prime the tubing, this means insulin has gone through the cannula, correct? I then insert the infusion set and the final step is to “fill cannula.” When I do that, isn’t the cannula already full from when I primed the tubing and doesn’t that mean the amount I put in for the fill (.3 units in my case) is then actually injected into my body? I just did a set change this morning and now I’m skating the edge of a low from breakfast and I’m pretty certain it’s from the “fill cannula” step, which is what leads me to ask the question. Your thoughts and insights are much appreciated.
cannulas have no insulin in them when you prime the tubing because THERE IS A NEEDLE IN THE CANNULA at that point in time. so there is empty space when the needle is removed.
I used to use cannula sets. hate them. I only use Sure-T’s (for MM pumps) which DO NOT need any additional insulin after the tubing/set has been filled with insulin. Therefore, I hit the ESCAPE button FOUR TIMES after I’ve primed the tubing, because I need no additional insulin once the tubing and set is filled prior to insertion into my body. makes for a faster set change.
Ahhhh, here I thought the cannula was in the needle, but clearly that could not be the case had I stopped to think about how big the cannula is. Thanks for that explanation. Not sure where the low came from, but it’s better than a soaring high.
So far the Insets are working fine. I like that I can use the 6mm, but I know I may run into challenges down the road.
You’re welcome! It’s nice to have cannula or needle-length options in sets. I use the shortest ones I can get as they work well.
When considering whether or not to “fill the tubing” I suppose there are a number of personal factors to consider.
What first comes to mind is just how sensitive are you to insulin? For me, usually a tenth or so of a unit is not going to make that much of a difference, so I don’t worry about it. But someone who is extremely sensitive to a difference of a tenth of a unit would probably need to be more careful.
The other side of this is that my insulin sensitivity is not constant. If I spend a day just sitting I’ll require more insulin than if I am up and moving around. I can eat the same things and deliver the same amount of insulin on two different days but will go low on one of them as a consequence of the intense physical activity from, say, using the vacuum cleaner.
Very. My IS factor is 1:100 and my TDD averages 15 units.
I have similar experiences to John. However, lately, due to low carbing everything is becoming more predicitable with regards to both my bg’s and my insulin requirements. Wish I had been low carbing long ago!
Then possibly you might want to experiment with the amounts you use when filling the cannula. Instead of 0.3 units maybe try 0.2 … or whatever gradations your pump allows … a few times and see if this makes a consistent difference?
A lot of these things others can talk about with you and relate what we’ve tried and how we think it worked for us, but ultimately what matters is how what you do affects your body in particular. <sigh /> 
Very true, but the thread ultimately answered the question I had about the cannula, so it will be easier to experiment now that I have a better understanding of what is actually going on with the cannula upon insertion.
I guess I am “the thread”?
Didn’t mean to slight you or overlook the fact that you were the person who specifically answered my question. I simply meant that I asked a very specific question and it was indeed answered in the course of the thread – answered by @phoenixbound. 
I’m not offended. I just thought it funny that the reference was to “the thread”. it’s all good. You thanked me earlier, so I don’t feel as if you ignored me in any way.
[quote=“Shadow2, post:9, topic:46433”]
… the thread ultimately answered the question
[/quote] just struck me funny.
I agree, it does seem funny in light of the actual facts. I think when I said it I was primarily focused on clarifying that I wasn’t asking for some vague general advice regarding what to do when I change the site. Rather, I was honestly confused about the fill cannula function and you had the answer.
I have a question since you said you are new at tthis. Have you read Walsh’s Pumping Insulin book? I think most people who go on line and pump already know about it but thought I’d mention it. Many of us consider it “the Bible” for pumping. Another book lots of people like is Think Like a Pancreas.
I have read Pumping Insulin more than a few times. I like that it is easy to understand and covers lots of the ins and outs.
I’ve been MDI for four years and I’ve read Think Like a Pancreas and Using Insulin. I didn’t actually find them that useful because they lean toward the “rules of thumb” in their explanations. As a LADA/T1 who didn’t need basal for 18 months and still only uses 5 units basal per day, it seems few of the generalized thoughts seem to apply. For that reason, I haven’t been too eager to get Pumping Insulin, but I still might go ahead and get it. Other than the “fill cannula” question, I haven’t really had any pumping questions arise - yet.
fair enough. 
. . . . . . . . . .
I’ll check these two books! This is the first time I hear about them but again I’m also new to pumping 
I’ve gotten the “Islands and Insulin: A Diabetic Sailor’s Memoir” and “Life is short laundry is eternal” both talk and discuss or i guess are about diabetes. I’m a huge reading lover and wanted to read something where the main character is diabetic.
Thank you.
Also thanks @Shadow2 interesting question, I’ll make sure to notice what happens when I change my infusion set and fill my cannula. I also fill it wit .3
however, my insulin sensitivity is 1:50