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Thread: CGMS ISIG and Calibration Guidelines

  1. #31

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    I saw in one of your other posts that you are a pediatric nurse who raised a T1 child from age 8 weeks. However, the tools now available for D management are completely different now vs. 3 years ago.


    I find your above statement condescending and dismissive. You seem to assume that my knowledge of diabetes is outdated. You also seem to have missed among my credentials that I am a nurse practitioner, and have current board certification in advanced diabetes management. I have worked with nearly a thousand kids with diabetes over the years. Your sample of one child, for three years, is not terribly impressive by comparison. What works for one may not for another.

    I remain concerned about the long-term effects on the psychosocial development of any child who is subjected to compulsive diabetes management.

  2. #32
    Join Date
    May 2008
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    Philadelphia
    Posts
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    I edited the OP today with the following addition:

    Edited 8-10-2009 - A tip to get good initial calibrations with the MM CGM - install the sensor at least
    2 hours before attaching the transmitter. We do this by installing the new sensor at night, then switching
    over the transmitter in the morning. This has helped get more consistetly good initial calibrations.

    This is after doing this ourselves for the past year, and also hearing from others who do the same thing.

    The MM sensor usually works just fine without doing this, but in our experience the first cal's are more consistently accurate if the new sensor has been in place overnight prior to the transmitter switchover.
    My daughter Leah was dx at age 8. Has used the Omnipod since 2007, Guardian 2007-2013, Dexcom 2007-present and sang the National Anthem at the 2013 JDRF Walk!

    DCCT: The Study That Forever Changed Treatment of Type 1 Diabetes - Improved Glycemic Control in T1 children Using Real-Time CGMS

  3. #33

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    Quote Originally Posted by Darryl View Post
    Edited 8-10-2009 - A tip to get good initial calibrations with the MM CGM - install the sensor at least
    2 hours before attaching the transmitter. We do this by installing the new sensor at night, then switching
    over the transmitter in the morning. This has helped get more consistetly good initial calibrations.
    Do you cover the sensor with something? I've always just assumed that the pointy end that goes into the transmitter is sensitive and haven't wanted to get lint, tape or bandaid adhesive, dog hair (!), etc in it. And I worry that the sensor would fall off overnight, particularly with a 5 year old pulling shirts on and off. What do people do to keep it fresh?
    Rachel
    mom to DS (8) diagnosed 4/06
    - pumping since 9/06 and CGMing since 3/07
    - MiniMed Revel 523 with Apidra insulin
    mom to DD (a lively tot)

  4. #34

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    Quote Originally Posted by Rachel View Post
    Do you cover the sensor with something? I've always just assumed that the pointy end that goes into the transmitter is sensitive and haven't wanted to get lint, tape or bandaid adhesive, dog hair (!), etc in it. And I worry that the sensor would fall off overnight, particularly with a 5 year old pulling shirts on and off. What do people do to keep it fresh?
    Thank you for getting this bizarrely derailed thread back on track. Who would have thought that someone could singlehandedly make a thread on calibration techniques for the MM CGM controversial?

    I put a small piece of Opsite over the "flat" purple part of the sensor. Jack wears his on his bottom, and his underwear protects it too. But the pointy end is unprotected, and we've never had an issue with it. I do believe that it is not waterproof unless the transmitter is connected, so they can't take a bath or anything this way.
    Last edited by hawkeyegirl; 08-11-2009 at 11:16 AM.
    Mom to J., age 13
    Dx 2007 @ age 3
    Medtronic pump and CGM (4/2008-6/2013)
    Tandem t:slim and Dexcom G5 CGM (current)

  5. #35
    Join Date
    May 2008
    Location
    Philadelphia
    Posts
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    Quote Originally Posted by Rachel View Post
    Do you cover the sensor with something? I've always just assumed that the pointy end that goes into the transmitter is sensitive and haven't wanted to get lint, tape or bandaid adhesive, dog hair (!), etc in it. And I worry that the sensor would fall off overnight, particularly with a 5 year old pulling shirts on and off. What do people do to keep it fresh?

    We use the upper butt area, and it has not been necessary to cover/protect the sensor so far. We do, however tape both the plastic and adhesive tabs down with tegaderm as soon as the sensor is installed.

    Depending on the location, it might be good to tape the sensor down with a band-aid or something that would not adhere.

    ETA - As Rachel said, we do not allow it to get wet (bath, etc.) the next morning until after it is connected to the transmitter.
    Last edited by Darryl; 08-11-2009 at 04:04 PM.
    My daughter Leah was dx at age 8. Has used the Omnipod since 2007, Guardian 2007-2013, Dexcom 2007-present and sang the National Anthem at the 2013 JDRF Walk!

    DCCT: The Study That Forever Changed Treatment of Type 1 Diabetes - Improved Glycemic Control in T1 children Using Real-Time CGMS

  6. #36

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    My spouse was speaking to Medtronic about calibrations errors and she was given the secret formula to determine when the pump would accept a calibration vs. giving a cal error.

    BG divided by ISIG needs to be in the range of 1.5 - 20. Outside of this range and you'll get the calibration error.

    We're in Canada and need to include the mmol/mg conversion, so for us the formula is BG * 18 / ISIG.

    We had been having low ISIG numbers, so BG's that we thought should work were giving us errors.

  7. #37

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    Darryl,

    So i think I have been doing this wrong for awhile, can you please help me? We usually do sensor inserts about 2 hours after dinner, no snack that night so that would give us like 4 hours after bolus/ food before it requests the 2 cal #'s. Im a night owl so I thought since this is a fairly stable time for her it would be ok, as long as its done by 12 am as she tends to get wonky some nights after this. Can you explain to an idiot what the ISIG is? We didnt get any training with our dex, it was more like call us with any problems kind of thing . Thank you SO much for sharing your wisdom! I am in aww of your success with CGMS and D management. I dont always trust the number but do tend to rely alot on the trending arrows. Thanks alot!
    Mom to Mikaila, 11 yo dx 08/09
    Pumping with a pink PING since 2/10 and Dexting since 3/10
    a1c at dx 15.4, 9/09 11.1, 3/10 7.0, 6/10 6.6
    Jordyn 10, trial net testing - neg
    Britt 17

  8. #38
    Join Date
    May 2008
    Location
    Philadelphia
    Posts
    4,313

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    The timing of your insertions sounds good.

    To explain the ISIG: The sensor puts out an electric signal which goes up as BG goes up. That signal is a number (the ISIG, or Input Signal) which is typically around "10" for a BG of 100, but varies from sensor to sensor.

    The sensor sends its ISIG to the receiver every 5 minutes. The ISIG alone is not enough for the receiver to know the BG. However, when you calibrate, this is what happens:

    Let's say the receiver is reading an ISIG of 10 from the sensor.
    You do a BG check and see that BG is 100, then calibrate the receiver.
    Now, the receiver knows that an ISIG of 10 lines up with a BG of 100.

    Next, let's say the ISIG doubles from from 10 to 20
    The receiver then knows that the BG doubled, and is now 200

    So, the ISIG is just a number. The receiver uses the ISIG, along with the last calibration, to compute the BG.

    The ISIG is useful because it tells you how your sensor is doing. If a new sensor has an ISIG of 10 for a BG of 100, then on day 7 the ISIG is only
    5 for a BG of 100, you know that your sensor has lost half it's strength on day 7.

    Or, let's say on day 2, you measure a BG of 200 and ISIG is 10, that is a clue that the fingers may have had sugar on them, causing an erroneous high BG reading. In this case, the ISIG could give a hint to repeat the BG check, and save you from a bad low.
    My daughter Leah was dx at age 8. Has used the Omnipod since 2007, Guardian 2007-2013, Dexcom 2007-present and sang the National Anthem at the 2013 JDRF Walk!

    DCCT: The Study That Forever Changed Treatment of Type 1 Diabetes - Improved Glycemic Control in T1 children Using Real-Time CGMS

  9. #39

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    Quote Originally Posted by MikailasMom View Post
    Darryl,

    So i think I have been doing this wrong for awhile, can you please help me? We usually do sensor inserts about 2 hours after dinner, no snack that night so that would give us like 4 hours after bolus/ food before it requests the 2 cal #'s. Im a night owl so I thought since this is a fairly stable time for her it would be ok, as long as its done by 12 am as she tends to get wonky some nights after this. Can you explain to an idiot what the ISIG is? We didnt get any training with our dex, it was more like call us with any problems kind of thing . Thank you SO much for sharing your wisdom! I am in aww of your success with CGMS and D management. I dont always trust the number but do tend to rely alot on the trending arrows. Thanks alot!
    ISIG is a MiniMed thing. The Dexcom doesn't give you access to this information.

    Also, we found that nighttime startups on the Dex really didn't work that well. We learned quickly not to calibrate after bed time - it led to inaccurate numbers.

  10. #40

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    newbie with CGMing here...have a few questions:
    1. When to calibrate with a toddler whom is eating almost ALL the time and nursing at night? Ideas, tips?
    2. Do you calibrate only when you're not also giving insulin?
    3. How do you know when the sensor is dying? I ask this because our endo said Isaac's readings from the CGM are fabulous compared to what she's seen with other kiddos his age, however due to how quickly his BG rises or falls it can be off by almost 100pts. I was told that the sensor is toast when it's off frequently, but this is often. We really are more so utilizing the CGM for finding trends, not for specific numbers KWIM.
    4. Do you store your sensors in the fridge? Somebody mentioned this and I wanted to know if this really helped.
    Sarah
    wife to TJ (t1d for 20yrs) MDI lantus/humalog
    mother to Ethan (non-d) 9 years old
    and Isaac (dx 11/09 at 19 months old) 7 years old, pumping on Animas after using MMRevel(6wks post dx) with Humalog and Dexcom G4 (love it!!!)
    ~dx with Celiac Disease July 2013

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