I think the hardest part of the CGMS system is CALIBRATION!! Anyone who is using this technology, or knows people who are - will agree or know what I am talking about.
Two weeks ago I started using the 522 Minimed CGMS system. The first glucose sensor I inserted went excellent. I spent the first day staring at the pump screen....amazed at the technology and amazed at the steady straight line for the glucose values. I stayed between 4 and 7 for the first day or two.....at this point I through "this is GREAT!!!"....usually I have issues with "dawn phenomon"....rising BG's in the early morning while I am sleepng. This did not happen the first night I was using the system - but the second night WHOA! I woke around 3am when my pump was alarming me that my BG was at 11.0 mmol/L. Being half asleep....I silenced the alarm and rolled over in bed. Later in the morning the alarm went off again.....and while still sleeping, I turned it off. When I woke that morning my pump showed I was still around the 11 mmol / L level on the pump screen - and the pump was asking me for my 12hr calibration glucose reading.....and then the problems began. As I was instructed, I tested with my BD meter that is linked to the pump. My glucose was around 15 or so...and within 15 minutes my pump was alarming "CAL ERROR". It was asking for another reading. Now this is the first time I encountered this alarm - so I went right ahead and tested again. WRONGO!!! I proceeded with a second "CAL ERROR"..and then the dreaded "BAD SENSOR" alarm. I called Minimed hotline - they said this sensor was DEAD and no longer good. 2 CAL ERRORS in a row kills the sensor. I tried several times to restart NO GO.
SO sensor #1 was scrapped after 3 days...I was hoping to get longer out of it. Same story with sensor #2....2 CAL ERRORS meaning BAD SENSOR.
What did I learn? After talking with Minimed customer support I was told to NOT CALIBRATE unless my BG was stable. So this meant I had to calibrate at least 3 hrs after eating or after a correction bolus, or a few hours before eating. Now I work shift work - so it is often hard to find these criteria in my day!! No easy!!! Sensor # 3 I used got caught in this CAL ERROR again - but I understood why it occured this time. Again it was because of the "dawn phenomon" rise. I have learned to avoid these CAL ERRORS I need to reduce the fluctuations. That I am sure will only benefit me in the long run - but it shows that these glucose sensors are "sensitive" and I consider them fragile.
So the sensors are calibrated every 12 hours - and these calibrations can not be done if there are any flucuations ongoing at that time. I am at work now - and my pump is alarming for a calibration - but I just ate dinner (working a night shift as well...sigh....) and I am not able to calibrate now with food in my belly and a bolus on board. So for the next several hours I can not calibrate or I run the risk of a "CAL ERROR"...and just two and this sensor is GONE!
My insurance company does not cover the sensors...or the tegaderms.....or the transmitter...or the transmitter anchors.....so to do these changes as often as I have been doing is expensive. For the past few days I have been being extra careful when I have to calibrate. I am waiting for what I feel will be a stable time with my glucose before calibrating. I leave the pump showing "overdue for calibration" until I feel it is ok --> to avoid ruining the sensor!!
It is worth it tho - this technology is GREAT, aside from the calibration. Most of the time the glucose values on the pump are withing .5 mmol/L to 1.0 mmol/L of the meter readings. I figure with some pratice I will work a routine for sensor starts and for calibrations. I don't really have a normal lifestyle - but I guess I will need to comprimse a bit for the sake of my sainity!! HA!
SOOO the main point I am getting at: IF YOU GET A CAL ERROR......WAIT....WAIT.....WAIT. This means your sugars are either rising or dropping quickly and the meter reading you are giving is different from the sensor reading (I find it lags appro 10 minutes). Give your body time to settle down - often an hour or so...leave your pump showing "Calibration reading overdue" until you can confirm your body is realy (use a non linnked meter to test glucose first). Anything you need to do to avoid these CAL ERRORS. You only get TWO chances!! I am sitting with a CAL error now on my pump - tried to calibrate soon after eating supper. WHAT WAS I THINKING? It is 1:30 in the morning...I am here at work all night, so I will wait until 03:00 and try again....
Anyone have any hints for calibrations??
Any hints for the CAL ERRORS?
Any hints for once you get a BAD SENSOR error after two Cal Errors? (ie any way to save the sensor???)
The learning curve is steep....I am working through my questions....next after I get the calibrations down will be learning more about this isig value......Cheers.........Drea.