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 Connector to MiniLink or iPro Sensor Electrode inside the needle Body

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

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

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

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

Glucose and Oxygen Enter Membrane 1 A semi permeable membrane that is very selective to glucose and oxygen The Membrane is required for biocompatibility In subcutaneous tissue Glucose = 72 to 360 mg/dl Oxygen = 0.9 mg/dl Glucose is 5 times more prevalent in subcutaneous tissue Membrane Enzyme Electrode

Glucose and Oxygen Enter Membrane 1 Glucose and Oxygen When the glucose and oxygen come in contact with the glucose oxidase enzyme, the first chemical reaction takes place Membrane Enzyme Electrode

First Chemical Reaction 2 Glucose and oxygen come in contact with the glucose oxidase enzyme Glucose and oxygen are converted into Hydrogen Peroxide (H2O2) and gluconic acid Glucose and Oxygen Membrane Gly Acid H2O2 Enzyme Electrode

Second Chemical Reaction 3 H2O2 seeps through to the Electrode layer A voltage is applied to the Electrode, causing H2O2 to breakdown into: Hydrogen Oxygen 2 electrons Membrane H2O2 Enzyme 2e- Electrode The more glucose in your body, the more H2O2 generated. The more H2O2, 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 2e- Electrode ISIG The ISIG is Proportional to Glucose Concentration

Converting ISIG to a Glucose Sensor Value 1 2 3 Check glucose level with a BG meter Enter BG reading into the insulin pump or monitor Accept BG reading as a calibration 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 128 112 Example: Cal Factor = 10 ISIG BG (mg/dL) 10.8 11.2 12.8 2e- 2e- ISIG = 11.2 12.8 108 112 128 calibrated 00:05 min 00:10 min