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Re: [IP] Pumping Questions

At 06:13 PM 11/23/98  Richard Aleksander wrote:
>Every user swears by his pump.  Minimed users report what I consider a
>disturbing frequency of no-delivery alarms, a problem I feel stems from its
>lower pumping pressures and use of plastic cartridges (see below).  Even so,
>Minimed pumpers report being satisfied with the remediation to their
>problems and its users swear by their pumps also.

Three points. The frequency of MiniMed complaints has to be balanced with
the fact that 80% of the pumpers in the US are MiniMed users. So, naturally
there will seem like there are more complaints about MiniMed than
Disetronics. The second point is that a number of the problems with "no
delivery" come from the infusion set, tubing and site problems, not just
the pump. Also, pumpers that use buffered insulins seem to have fewer
problems than others... although modern tubing and cannulas are supposed to
prevent insulin crystallization. The third point is that only people with
problems post this type of information. Everyone who's MinMed pump is
working fine doesn't write just say this. So, you'd have to find the real
percentage of people who are having problems... my personal guess is that
it would be a very small percentage of actual users. 

>Disetronic sends two pumps, as the pump is programmed to turn off for
>factory service after two years of pumping.  After service at the factory
>each pump is returned with an additional two years of warranted service.
>The extra pump can be used anytime as a back up.  Minimed sends one.

Disentronics is required by Swiss law to send two pumps. The MiniMed has no
mandatory timed required factory service. There are many long-term MiniMed
users in this group with virtually no problems. A call to MiniMed will have
a replacement pump at your door within 24 hours. Just as a side-note, all
pumpers should be prepared to give injections if necessary... you never
know when you'll be on the road and need to give yourself a boost when
disaster strikes... or you've run out of insulin in your pump at an very
inopportune time.  

>Minimed uses a solenoid to push insulin a tenth of a unit at a time.  If a
>user has a basal dose of 8-tenths of a unit hourly, the Minimed will click
>eight times an hour, or once about every seven and half minutes.  In
>delivery of boluses of, say, 6-1/2 units, the Minimed will click 65 times
>and it will take several minutes to deliver.

I've never found this to be a problem at all... the fact that it takes a
minute or two more to deliver can't make much of a difference in the real
world. And, since food is absorbed gradually into bloodstream (not all at
once), it may even be an advantage. The square-wave bolus feature of the
MiniMed is in fact designed to purposefully spread the insulin out over a
period of time when eating foods with a high glycemic value. Other people
have medical problems with food digestion that also requires that the
insulin be spread out over time.

>There's another fairly important difference between the two pumps related to
>Humalog, with the Disetronic holding an advantage.  The cartridges for the
>Disetronic can be plastic or glass.  Glass costs more and is the preferred
>material.  All Minimed cartridges are plastic.
>Plastic cartridges tend to degrade Humalog molecularly.  The Humalog is
>attracted ionically to the plastic wall of the cartridge.  The plastic ones
>also present more opportunity or propensity for contamination with air.

I've never read anything which says that the plastic used in the reservoir
degrades Humalog. For the 3 days that it's in the cartridge, is there a
real significant difference?? Since I've never heard this before, would you
please provide journal citations or other scientific evidence? I'd be very
interested in reading about this phenomena.

>Humalog has some degradability properties that are problematic for pump
>users.  Many of the Minimed users find they have potency/delivery problems
>before their cartridges empty, and they have to change them sooner.  Many
>also report they have to dilute their Humalog for various reasons.

The main reason Humalog degrades, from what I've seen on this list, is
heat. Obviously heat would affect all pumps and reservoirs equally. I
personally have never noticed any potency problems using plastic reservoirs
with Humalog. After 3 to 3 1/2 days it's still working strong. Also, the
mixing of insulins has nothing to do with the MiniMed pump. It's a
technique to balance the longer term effect of a "regular" type insulin
with the shorter acting Humalog and can be used with either pump. Since
everyone reacts differently to different insulins it's just another method
of making the pump more effective for specific individuals and conditions. 

>Plastic cartridges cannot be prefilled with Humalog that far in advance.
>And even if they fill them just before placing the cartridge in the pump,
>the Humalog remaining in the used factory-filled vial may be degraded as
>well, perhaps by as much as 30 percent.

I have never seen evidence of a 30% degradation of Humalog in the original
vial or in the reservoir unless it had gotten very warm. If you keep it
reasonably cool I've found that it will be just fine. I keep my reserve
supply in the refrigerator, but bring it to room temperature before loading
the reservoir. This is supposed to keep the air bubbles to a minimum. 

>My opinion is those with Teflon catheters inserted at shallow angles
>(Minimed's silhouette and Disetronic's tender) are superior to metal needles
>or Teflon inserted perpendicular through the skin.  Subjectively, I find
>them more comfortable.  Objectively they are more slender.  Appealing to me
>are their quick disconnects at the catheter (no pony-tail hanging off like
>on the Minimed sofset).

I agree. I've used the Silhouettes for 6 months and find them very
comfortable. However, this is an extremely personal issue. Everyone reacts
differently. There are a number of people on this list that will only use
the metal needles... others swear by the soft-sets. My advice would be to
look at the options and try one or two... then make a choice based on what
works best for you.

Insulin-Pumpers website http://www.insulin-pumpers.org/