Pumping Insulin A Few Days on the MM Glucose Sensor

By Mary Jean Renstrom

On Wednesday, Dec. 1, 1999 I began a 72 hour test of the new MiniMed Continuous Glucose Sensor. The sensor reads glucose in interstitial fluid through a small cannula inserted under the skin, similar to an infusion set. The sensor is connected with a small electrical cable to an electronic device that you clip to your belt or put in a pocket. The device is about the same size as an insulin pump. It was comfortable to wear, most of the time I didn't even know it was there.

Each time I tested my bg with my meter, I entered the results into the sensor as a calibration check. If the numbers had been vastly different, the sensor would have alarmed. My meter readings are the little squares on the graphs. I was also to enter an "event" any time I ate, gave myself insulin, or exercised. These events are recorded as symbols at the bottom of the daily graphs.

The data needs a bit of explanation. It would make more sense if you could see my food log, but since you can't, I'll fill in a few gaps:


12-1-99: Everything worked great for this day. The coefficient of correlation between my meter and the sensor was 96%.



12-2-99: I ate a high fat lunch at 1:00. I used a dual wave bolus with half of the insulin immediately and the other half spread over one hour. I decided not to correct for the high bg at 3:00, knowing that the insulin from my square wave had not finished peaking yet. Looks like it worked.



12-3-99: On this day, I decided to do a fasting check of my basal rates after breakfast. I had some problems with hypoglycemia. At 9:00 a.m. and 1:30 p.m., I ate 9 grams of glucose to correct the lows. The graph indicates that my bg went below 40 (the lowest level the sensor measures) several times. However, I don't think my bg was this low. The coefficient of correlation between my meter and the sensor for this day was 69%.



12-4-99: I ended the trial at 9:00 a.m. I did bolus and eat breakfast at 8:00 a.m., but forgot to enter those facts into the sensor.



Here's the summary data showing the meter readings I entered and the correlation between the meter readings and the sensor data, etc...
Data Summary
 Optimal Accuracy CriteriaSensorMeter
Date# Paired
Sensor/Meter
Readings
Correlation
Coefficient
[r]
Mean
Absolute
Error (%)
Number
of
Readings
Average
(mg/dL)
SD
(mg/dL)
Sensor
Range
(mg/dL)
Number
of
Readings
Average
(mg/dL)
SD
(mg/dL)
Meter
Range
(mg/dL)
12-01-9970.9681671263176-184713635101-191
12-02-9980.86192881305140-238814639104-221
12-03-99 x70.6925288653240-1787922854-141
12-04-99 x1n/a0107783540-162178078-78
All Days230.88168501015040-238231234254-221
 
x: This day does not satisfy the criteria for optimal accuracy as indicated by the shaded entries in the summary table.
    Please use your clinical judgement in evaluating the graph.
 
c: The calibration slope for this day is outside the allowable range of 2 to 10 or no paired sensor/meter data
    are available. As a result, no sensor plot is provided.


Overall, it was a valuable experience. I was surprised to see the peaks and valleys between my meter readings. Most importantly, I have discovered that I have nocturnal hypoglycemia, and I sleep right through it. I'll be adjusting my basal rates to cover this.

Mary Jean Renstrom


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