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Book Review: Practical CGM

Sep 7, 2015

Our Doctor of Pharmacy Candidate from LECOM College of Pharmacy, Diana Jules, has reviewed a new book from the ADA and found that it is a good read for you. See what she has to say.

altBook Review: Practical CGM


Diana Jules, Doctor of Pharmacy Candidate USF College of Pharmacy

By Gary Scheiner, MS, CDE; Abe Ogden, Director, Book Publishing; Greg Guthrie, Managing Editor. American Diabetes Association, Inc. ®, Alexandria, Virginia: 2015.

I. Introduction
Finger stick glucose meters allow patients to get a snap shot of their glucose readings, however continuous glucose monitoring (CGM) would provide more than a snap shot. CGM would provide the full picture of glucose trends and the effect of insulin and medications on blood glucose.

II. Design
CGM is equipped with a sensor, a transmitter, and a receiver or display. The sensor is designed in a thin, flexible, metallic filament fashion. The sensor is about a finger-width long and it is placed in the layer of fat underneath the skin. The insertion of the sensor is painless and should be replaced every week. Many patients claim that the sensor can be use longer than a week, however there are no studies to support that claim. The transmitter is the size of a thumbnail and is connected to the sensor. When the sensor interacts with glucose particles, an electrical current is generated which travels to the transmitter. The transmitter contains its own power source and radio transmitter. Dexcom CGM utilizes a handheld receiver that is the size of a small cellphone. The receiver displays basic high and low alerts, rate-of-change alerts, and predictive alerts. The basic high and low alerts are warnings for hypoglycemic or hyperglycemic events. The-rate-of-change alerts are warnings to the patients when the blood sugar is falling or rising faster than the normal rate. The predictive alerts are warnings of high and low rate-of-change. The Medtronic CGM display is incorporated into the Medtronic insulin pump. Both the Medtronic and Dexcom are provided with software for downloading and displaying data from the receiver. Medtronic utilizes CareLink Pro which is an office-based software that patients can use in the comfort of their home.

III. Benefits
Health professional organizations believe that CGM is ideal for adults and children administering insulin. CGM would be beneficial in 1) checking blood glucose regularly in a patient committed to intensive diabetes management 2) monitoring glucose in patients with frequent hypoglycemia, patients involve in sports, or patients engage in high-risk professions 3) observing patients entering a change in therapy.

Other benefits from CGM are the use of the numbers, trending information, high/low alerts, and pump integration. In terms of the use of the numbers, CGM updates the glucose levels every 5 minutes. The value that is displayed every 5 minutes is an average of the data gathered over the previous 5-min time interval. CGM provides information on whether the glucose trend is stable, rising, or falling. CGM systems allow patients to identify trends in two ways which are on-screen direction arrows and trend graphs. Each arrow would correspond to glucose values. There are arrows to inform the patient if their glucose is stable, falling modestly, falling rapidly, rising modestly, or rising rapidly. This information allows the patient to know where their glucose is heading and ultimately impacts the patients’ next step. The CGM alerts the patient when the glucose is high or low. Many patients who utilizes insulin often times experience hypoglycemia because they are unaware of their glucose levels. Some patients can slip from moderate to severe hypoglycemia without recognizing the classic symptoms that are commonly associated with hypoglycemia. CGM provides a warning signal for mild hypoglycemia and hyperglycemia. CGM can be integrated with an insulin pump which provides real time data these have a “low shut off” capability which allows basal insulin administration to stop for 2 hours in present of hypoglycemia. If the sensor concentration falls below the threshold, then the low shut-off feature will be activated. Research has shown that the low shut off feature in the Medtronic device reduced the incidence of nighttime hypoglycemia by 30%.

IV. Challenges
One of the major challenges of CGM is that the information that is provided is slightly inaccurate and has a lag time. CGM does not measure blood glucose concentration directly, however it does measure the glucose concentration in the fluid surrounding the fats cells underneath the skin. Based on the location of the sensor, it takes a long time for glucose to travel from the blood to the tissue and this creates a lag time. If a patient blood glucose is elevated, it would take a few minutes for the CGM to generate that trend. Since CGM does not collect blood glucose concentration then the data recorded is inaccurate. However, one could argue and state that the fingerstick glucose meter values differ by 5-10% from standard glucose laboratory values and older meters can vary by 10-20%. Based on the differences seen in a fingerstick glucose meter, the variability that is seen in CGM is not a big deal.

Another challenge with this system, which plays a major role in accuracy, is calibration. If the patients are not taught properly about the calibration procedure, then the system will not provide accurate information. Educating patients on the proper techniques means breaking them free of sloppy fingerstick habits that have been developed over several years. This creates a burden on physicians. To resolve this issue, teaching services can be provided by pharmacists to decrease the burden.

The CGM has many different alerts (basic high and low alerts, rate-of-change alerts, and predictive alerts), and patients may experience alert fatigue especially if the alerts are excessive. This can cause patients to ignore reminders in the future which could lead to a detrimental state of being. One possible solution to eliminate this situation is to avoid unnecessary reminder alerts. Patients should calibrate the CGM on a regular schedule including before bedtime (to prevent any nighttime calibration reminders). Also, frequent alerts will decrease the lifespan of the battery leading to a frequent charging or replacement of the battery. A solution to this issue is to charge devices on a regular basis.

V. Final Thoughts
The guide to CGM was written in a well fashioned manner. It presented how the sensor would be placed underneath the skin and the function of the transmitter and receiver. Also, it provided all the logistics about the mechanism of action of CGM. It explained many of the positive and negative attributes about the devices. Also, it presented solution for the common issues that users may come across. Currently, I believe that there is a greater need for this type of glucose monitoring in patients taking insulin. CGM can decrease the amount of hypoglycemia


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