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RE: [IPk] Medtronic Guardian RT CBGMS

Hi Carol,

I've been using the Guardian RT for a couple of months. In a way, I think it 
is a shame that you only have the loan for three days, as that isn't really 
long enough to learn how the unit works for you and to get to grips with the 
information the system gives you and how to interpret it.

It is important to remember that the Guardian RT is *not* a Continuous Blood 
Glucose Monitor. Rather, it measures the glucose in the interstitial fluid - 
the fluid between your cells. There is a relationship between interstitial 
fluid glucose and blood glucose, which is why the system works at all, but 
the numbers won't always be exactly the same. I think a good principle to 
remember when using a continuous monitor is not to take the numbers at face 
value. The information on the display could be given to you in any number, 
you have to learn what the number is telling you.

It is also very important not to look at a single number and respond to 
that. The Guardian RT, unlike the sensor augmented pump (522/722) and the 
next generation of the RT itself, has no trend information in the form of 
arrows or an on-screen graph, so you have to manually scroll back yourself 
through the recent numbers and try to draw a mental graph of which direction 
you are moving in and how quickly. This information  then needs to be 
integrated with factors such as how recently you ate and how much insulin is 
still active in your system e.g. a sharp rise within an hour of eating may 
well need no action, since it is explained by your meal, and you should, 
provided you have bolused, have the insulin on board to deal with it.

A couple of other important points: the Guardian will often lag behind your 
fingerstick results due to the lag in the change of glucose concentration in 
interstitial fluid, compared to blood glucose. The faster your blood glucose 
is moving, the greater the lag will be, particularly with low numbers. For 
this reason the low alert needs to be set very conservatively if you want to 
catch all lows before they happen. This is especially true if you have any 
degree of impaired hypo awareness. The lag with high numbers doesn't depend 
so much on how rapidly your bg is changing, but tends to be more 
predictable. For example, if my blood glucose is over 11, the Guardian will 
usually be around 2mmol behind. If I creep up to around 14, that rises to 
3mmol. This is where 'knowing what the numbers mean' that I referred to 
earlier comes in. I can translate 9's on the Guardian to 11's and so on. 
Again, I set the alert quite conservatively.

Most importantly of all though: the Guardian does get it wrong. I'm sure 
you've been told to always check with a fingerstick before taking action! In 
my experience, the trend is almost always right, but the numbers won't 
always be.

Calibration obviously has an impact on accuracy. I, and others, have found 
that calibrating only when your bg is fairly stable (i.e. not after a meal 
or exercise when it may change rapidly) is important. I also try to 
calibrate only at times where the fingerstick and Guardian are in fairly 
close agreement. This may seem daft, but it works. I often have a slight 
"damn you Guardian... you're wrong" feeling and want to feed in the real 
number, but in practice this tends to lead to CAL errors which in turn can 
lead you to having to re-initialise the sensor, which takes two hours!

I don't know if you have access to the software, but this is one of the most 
useful aspects to me as it allows you to see day to day patterns in the rise 
and fall very easily, which along with fingerstick data is great for 
adjusting basal rates or visually seeing the impact of food and exercise. 
Unfortunately three days is not really long enough to experience a wide 
range of experiences to get data on.

I hope you get some useful information out of your time with the Guardian 
though. It is definitely a great tool and I really think continuous 
monitoring is the future. As newer generation products come out, the 
technology can only improve. We just need to remember to shift our 
perceptions of data from what we have with the 'snapshots' of fingerstick 

If you have any other questions, ask away!

Type 1 23+ Pumper 4+

>Is anyone out there currently using one of these monitors? I would be glad
>to "talk" to someone who is - I currently have one on a 3-day loan from the
>Medtronic rep.
>Type 1 nearly 30 years, pumping 1 year.

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