How the Glucose Sensor Works

Continuous Glucose Monitoring

Objective • To learn the components of the Glucose Sensor and how the Glucose Sensor works in interstitial fluid Key Points • Proper technique when handling and inserting the Glucose Sensor as well as ongoing care leads to a successful CGM experience • The Glucose Sensor requires calibration with a blood glucose meter

Glucose Sensor Components Introducer Needle Handle Introducer Needle Sensor Electrode inside the needle Connector to MiniLink or

i

Pro Body

Glucose Sensor Components Introducer Needle Handle Never hold or pick the Sensor up by the needle handle Introducer Needle – 22 gauge (1/2 diameter) – Bevel faces down – Discard after insertion Sensor Electrode inside the needle Connector Attaches to the MiniLink Transmitter or i Pro Recorder Body Pick up the Sensor on either side of the Connector

The Sensor Electrode Sits Inside the Introducer Needle Reference electrode Working electrode Counter electrode Closest to the skin Maintaining an Optimal Sensor Placement Ensures Success

Layers of the Glucose Sensor Semi Permeable Membrane Selective to glucose and oxygen Enzyme The membrane surrounds a glucose oxydase enzyme Electrode Membrane Enzyme Electrode

Outermost Layer of the Glucose Sensor Semi Permeable Membrane Selective to glucose and oxygen • Ensures biocompatibility • Maintains the required glucose to oxygen ratio required for diffusion to the enzyme layer • Functions as a glucose limiting membrane

Membrane

Enzyme Electrode

The Glucose Sensor Consists of 3 Layers Semi Permeable Membrane Selective to glucose and oxygen Enzyme The membrane surrounds a glucose oxydase enzyme Electrode

1 Glucose and Oxygen Enter Membrane

A semi permeable membrane that is very selective to glucose and oxygen Membrane The Membrane is required for biocompatibility Enzyme In subcutaneous tissue Glucose = 72 to 360 mg/dl Oxygen = 0.9 mg/dl Electrode Glucose is 5 times more prevalent in subcutaneous tissue

1 Glucose and Oxygen Enter Membrane

• When the glucose and oxygen come in contact with the glucose oxidase enzyme, the first chemical reaction takes place

Glucose and Oxygen

Membrane Enzyme Electrode

2 First Chemical Reaction

• Glucose and oxygen come in contact with the glucose oxidase enzyme • Glucose and oxygen are converted into Hydrogen Peroxide (H 2 O 2 ) and gluconic acid Membrane Enzyme Electrode

Glucose and Oxygen Gly Acid 2

3 Second Chemical Reaction

• H 2 O 2 seeps through to the Electrode layer • A voltage is applied to the Electrode, causing H 2 O 2 to breakdown into:  Hydrogen  Oxygen  2 electrons Membrane Enzyme Electrode

H 2 O 2 2e-

The more glucose in your body, the more H 2 O 2 generated. The more H 2 O 2 , the more current generated.

Converting ISIG to a Glucose Sensor Value • The 2 electrons generate a current called ISIG • ISIG is converted to a sensor glucose value when a BG meter value is entered into the pump or monitor for calibration Membrane Enzyme Electrode The ISIG is Proportional to Glucose Concentration

2e ISIG

Converting ISIG to a Glucose Sensor Value

1

 Check glucose level with a BG meter

2

 Enter BG reading into the insulin pump or monitor  Accept BG reading as a calibration

3

 The insulin pump or monitor calculates the calibration factor:

Cal Factor

Meter BG / ISIG Sensors require calibration using a blood glucose meter

Converting ISIG to Sensor Glucose

Meter BG ISIG 2e-

ISIG Cal Factor = Meter BG / ISIG 108 mg/dL / 10.8 (ISIG) = 10

Calibration Factor Examples

Meter BG Glucose / ISIG = Cal Factor 108 mg/dL / 10.8 (ISIG) = 10 (Cal Factor) 10 (Cal Factor) x 10.8 (ISIG) = 108 mg/dL Cal Factor x ISIG = Glucose ISIG

10.8

Example: Cal Factor = 10

11.2

12.8

BG (mg/dL)

108 112 128 calibrated 00:05 min 00:10 min ISIG =