Continuous Glucose Monitoring (CGM)
V. Sanoe Harrison MD
Living Well With Diabetes Conference
CHOP – 3/28/15
Outline
• What is CGM, How does it work
– Glucose is turned into an electrical signal
• Why Use It?
– Improved A1c or average glucose
– Protection against hypoglycemia
– Decreased Variability
• How to Use it
Outline
• Limits and Challenges
– Accuracy
• Absolute
• Time Delay
– Sites and Skin
– Information overload
• Example/s
• Q&A
What is CGM
• Relatively new electrochemical sensors placed under the skin (subcutaneous tissue)
– MiniMed 1999
– Dexcom 2006
InterstitialFLuid
Interstitial Fluid
Semi‐permeable Membrane
Glucose Oxidase Embedded Layer
Hydrogen Peroxide
Gold or other Metal Core Pieces of CGM
Remote Monitoring
• Dexcom Share
• Medtronic MySentry
• Night Scout
Dexcom Share
• iPhone or iPod bluetooth
• Received on up to 5 devices
Medtronic MySentry
• Color Screen Display
• Power Supply
• Outpost – Transmits information from the Pump to the Monitor
– Enables you to monitor from up to 50 feet away
– This means that your child or loved one can be sleeping in one room while you are in another
Night Scout
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Non FDA approved
Build it yourself
Costs >$100 for parts
Website, Cell/Data Service
• http://www.nightscout.info/
Why Use CGM?
• Normal blood sugar = no complications
CGM in 24 Healthy Volunteers
Day Ave ± SD = 93.0 ± 7.0 mg/dl
Night Ave ± SD = 81.8 ± 6.3 mg/dl Power of Continuous Sensing
DCCT (Diabetes Control and Complication Trial)
mg/dL
120
150
180
240
270
300
DCCT (Diabetes Control and Complication Trial)
DCCT (Diabetes Control and Complication Trial)
Sensor Lowers HbA1c
/year
Decreases Hypoglycemia
How to use it
– Proper calibration
• Calibrate when the glucose is stable
Time Delay
Black: blood glucose
Red: CGM glucose
How to use it
– Real‐time benefits
• Predicting low or high sugar
– Reviewing Data
• Basal – Is my sugar stable overnight?
• Carb Ratio – Is it working?
• Sensitivity Factor – Is it working?
Date
3/26/2015 4:03:00 AM
3/26/2015 8:32:00 AM
Event
Carbs 56 grams
Insulin 2.3 units
Other Examples
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•
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Logging exercise, carbs, illness
Exercise (late hypoglycemia)
Over‐correction
Assessing basal rates (or Lantus)
Meal Assessment – ie Medtronic Pre/Post
Post‐meal Dosing
Minimed Patterns
DEXCOM‐Patterns
Hourly Stats
Glucose Distribution
Limits
• Accuracy
– Must be calibrated (at least 2 times/d)
– Mean Absolute Relative Difference (MARD)
• Sensors 14%
• POC glucometers 5‐10%
Challenges
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•
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Discomfort
Won’t stay on
Skin Reactions
Won’t work
Too many alarms
Feature
G4 Platinum by Dexcom
MiniMed 530G with Enlite
by Medtronic Diabetes Guardian® REAL‐Time by Medtronic Diabetes
Sensor life 7 days
6 days
3 days
Sample Frequency
Every 5 minutes
Every 5 minutes
Every 5 minutes
High/Low Alerts
Yes
Yes
Yes
Trending Arrows
Yes
Yes
Yes
Predictive Alerts
No
Yes
Yes
Insulin Delivery change based on glucose reading
No
Yes – Threshold Suspend feature (in response to LOW BG )
No
Range of Monitor to Transmitter 20 feet
6 feet
6 feet
Transmitter Waterproof
Yes, depth of 8 ft for 12 hrs
Yes, depth of 8 ft for 30 minutes
Yes, depth of 8 ft for 30 minutes
Calibration with blood Minimum every 12 hours glucose
Minimum every 12 hours
Minimum every 12 hours
Communicates with an insulin pump
YES – the Animas Vibe system
Yes
Yes – the MiniMed REVEL system Monitor size
4” x 1.8”
* Changes with pump integration 3” x 2”
Displays on insulin pump 3.2" x 2"
Download Capability
Dexcom Studio, Diasend Windows
Web‐based Carelink Personal Mac/Windows
Web‐based Carelink Personal Mac/Windows
Website
www.dexcom.com
www.medtronicdiabetes.com
www.medtronicdiabetes.com