De-mystifying the motor errors

Before Diabetes Blog Week started, you may recall that I was whining a bit about insulin pump motor errors.

Well, I don’t know what caused them – and Medtronic has certainly been willing to work with me so I don’t end up in a potentially troublesome situation (i.e. like Swampy, but asking “Where’s my Insulin?”), but I’ve decided to make a few changes on my own, just in case. But first…

Every time I’ve had a problem with my Revel, I wax nostalgia about my old Medtronic 515 which worked for years without even a hiccup. What’s different about that pump and this one? Well, first of all, the older one had much less precision with insulin delivery. I don’t know the numbers off the top of my head, but the old one only gave me the choice of one digit beyond the decimal point, while the newer one gives me a choice of at least two. That’s a tenfold increase in precision right there if you’re talking bolus.  But if you’re in the basal-domain, take the hourly basal and divide it by sixty minutes (or however often the pump delivers pieces of basal) and you’ve got some really tight tolerances.

Maybe those tighter tolerances mean a better ability to detect when the pump falls out of those tolerances? Though the official definition of a Motor Error is vague and circular at best,  The best definition I’ve heard of a motor error is that it occurs when the piston doesn’t line up where it’s expected. It makes sense to me, so I’m sticking with it.



This tiny thing might make all the difference

Getting back on track.  When I wore my 515, I always used the Activity Guard. It’s the little tiny clip at the end of the pump that keeps the reservoir from accidentally falling out — or something like that. My CDE at the time (who trained me on the pump, but is not a Medtronic employee) told me it’s pretty much useless. She never used it herself (she’s also a T1 Medtronic pumper) and found it a bit laughable that I bothered with this trivial element. Still, I used it religiously.

See the snapped locking-clip at the top? Proof that these things move.

See the snapped locking-clip at the top? Proof that these things move.

Until one day, while spending the weekend with relatives out-of-state relatives and doing a set change in a pre-teen’s messy bedroom (understatement!), I lost it. Yes, I worried a bit, but then accepted that I probably didn’t need it anyway, so I went on with life, sans-Activity Guard.

When I upgraded to the Revel, I still went on without the Activity Guard. Could something have possibly bumped the tip of the reservoir? Possibly. Could that, in turn, have bumped the piston? Possibly. Could that have resulted in the motor error? Maybe.

This is Riva’s artwork, not mine. She owns all rights and deserves all the credit. Used with permission.

And last Saturday, while everyone was admiring Reva’s diabetes body-art, I noticed that she has the activity-guard on her pump. (UPDATE 6/3/13: Thanks to Sara’s comment below, I realized that I was wrong. That’s a belt-clip, but it has the same twisty-locky-thing as the Activity Guard. But it’s still a cool piece of artwork, so I’m leaving the image intact.)

So maybe it really is worth using.

Purging the bubbles

Aside from not using the Activity Guard, I was given another piece of possibly ill-conceived advice – this about starting a new reservoir/infusion set. I was told that, after filling the reservoir and connecting the tubing, but before inserting it in the pump, that I should use the little removable plastic plunger to begin filling the tubing. This would give me an opportunity to flick some of the air bubbles into the tubing which could be purged out during the priming process.

In reality, I noticed that when I did that, it fought me. I would fill two inches of tubing, then an inch would get sucked back out. Push another two inches, another inch back. I’ve done this since my very first site change without concern.

But now I wonder. Why is it sucking back out? Am I causing too much pressure inside the assembly? Am I creating some sort of a vacuum? Is the initial “push” damaging the first section of tubing?

Again, I don’t know. But if insulin is “backing out” of the tubing, the plunger might be getting pushed back as well. Or not.

It’s a theory, and I don’t know how credible it is. But that could certainly cause the piston to move and cause a motor error. Even days after the site-change.


This one’s probably my fault

During my most recent motor error, I made a surprising – and surprisingly embarrassing – observation. At work, I had been using a portable two-way radio – a typical walkie-talkie style, that day. When I went to get lunch, I put the walkie-talkie in my jacket pocket and forgot about it.

I bolused for lunch, and halfway through I got the motor error. That’s when I realized: my pump was clipped near my hip on the left side. My jacket was hanging over the pump. Inside my left jacket pocket, not too far from the pump, was the walkie-talkie.

I wasn’t using the radio, it was just sitting there idle. But it was there.

The folks on the phone at Medtronic always ask if I’ve been near any “strong magnetic fields”. MRI’s, airport scanners, that sort of stuff. MRI’s are strong; they can pull an earring right out of your ear (or wherever you may have it). A cell phone doesn’t count. I’ve asked — repeatedly.

Still, I’m going to make a conscious effort no to keep any kind of cell phone, walkie-talkie, or transmitter of any type (CGM transmitter excepted) on the same side of my body as the pump.

It shouldn’t matter, but it just might…

If you use a pump, particularly a Medtronic, do you make any of the “mistakes” that I did? Do you think they really are mistakes?

Posted on May 23, 2013, in Diabetes, Insulin pump, Personal and tagged . Bookmark the permalink. 10 Comments.

  1. I don’t make the same mistakes (but you have me worried because I threw out my activity guard last week; never ever used it), but I have always used the cartridge plunger to “pre-prime”. If it doesn’t push easily, I’ve found it’s because the connection between cartridge and tubing isn’t sitting right. The cap is usually wonky. (Truth? One of your pics had a wonky cap angle, but I wasn’t sure if it was just the camera angle.)


    • Good point… I have tried to “pre-prime” (good term) and sometimes it just won’t go, and I find it’s not connected right. I guess I won’t know anymore if I don’t do it. (for the record, I’ve been told by others that there’s no need to pre-prime either…).

      I think I know the picture you’re talking of — it’s the one with all the air bubbles, right? I noticed that after it was posted. That was one that I had removed and had gone through painstaking efforts to get the bubbles in focus. I also don’t know if the apparent crooked-ness is due to the lighting and photography, the subsequent manipulation of the reservoir/tubing to get the right picture, or if it was that way from the start. I tend to believe it wouldn’t have worked at all if it was always that way, but there were those bubbles….

      I have a few extra Activity Guards lying around (long story). If you think you need one, let me know…


  2. FWIW, I used to pre-prime my MM and didn’t any issues with it…but that’s not to say it’s not causing some error for you. I’m voting the walkie-talkie thing. Keep us updated on how it goes.


  3. I don’t use the plunger to prime. I let the pump motor do the work. I’ve noticed that I’ll get a motor error if the bottom of my reservoir gets angled a bit (don’t ask me how that happens). Also, no activity guard. Just the belt clip.


  4. I never ever used the activity guard in 8 years of Medtronic. I also never ever had a motor error in 8 years of Medtronic – HOWEVER I stopped at the 522 because I had no desire to use their CGM.

    I actually don’t think that is an activity guard in the picture you posted of Reva’s. I think that is the lock on the low-profile pump clip. Fairly sure because that is the only clip I used.

    I am not sure about your filling technique, but I picked a trick up on the message boards a while back that has seemed to treat me well. Before I add the insulin, I take use the plunger to move the base up and down in the reservoir. I also twist it from side to side as I am doing this. No scientific proof but theoretically it loosens the path that the plunger/reservoir will follow as it delivers insulin. As far as actually priming the tubing, I let the pump do all the work.


    • Upon closer inspection, Sara, I believe you’re right; it’s not the activity-guard. I stand corrected.

      I’ve also learned to move the plunger up and down before filling it (and to partially unscrew it) before filling with insulin, but I never heard of the side-to-side thing.

      I am really, seriously thinking of switching to the Animas Vibe/Dex G4 combo when that comes out. I have a feeling that may come before the Enlite, and if it does I just might make the switch. My next step is to talk to people who’ve used both and learn of their preferences. So far I know of people who’ve gone from MedT to Animas, but no one whose made the reverse switch…


  5. P.S. the reason why I discounted your other theories was not especially clear now that I read it again. I really think there is something about the mechanics of the Revel that is causing the problem. I honestly cannot remember a single blog about a motor error problem before that version came out.


  1. Pingback: The reservoir | Rolling in the D


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