Continuous glucose monitoring (CGM) can be a wonderful tool to help people with diabetes manage their blood glucose levels. CGM systems use a thin wire sensor inserted into the fatty tissue just below the skin to detect glucose in the fluid between the cells (called the interstitial fluid). Information from the sensor is transmitted using radio waves to a receiver/monitor, which displays an estimate of the current glucose concentration. An updated glucose reading is provided every one to five minutes, depending on which system is being used, and the system can be set to sound an alarm if the glucose level goes above or below a target range set by the user. The monitor also displays line graphs showing glucose trends over the past several hours. Sensor data can be uploaded to a computer, where compatible software permits detailed analysis of glucose trends over longer time intervals. This type of information can be useful for making both daily decisions about diabetes care and decisions regarding a person’s overall diabetes regimen.
As helpful as the data from a CGM can be, getting accustomed to using one can take some time and can sometimes be frustrating. This article addresses some of the common questions that come up about CGMs and presents strategies for getting the most from continuous glucose monitoring.
Where should I insert the sensor?
A sensor can be inserted anywhere you give an injection or put in a pump infusion set. Ideally, it should be in an area where you can pinch up some skin. Typically, sensors are inserted into the fatty areas of the abdomen, buttocks, thighs, lower back, and arms. They should not be inserted into areas of hypertrophy (scar tissue from giving insulin in the same spot too many times) because they will not work as well in those areas. You should also avoid inserting a sensor into areas where your body naturally bends, since this can cause pain, irritation, and adhesion problems.
It was once believed that the sensor should be inserted at least one inch away from your infusion set or the site of your insulin injections, on the theory that having insulin too close to the sensor would cause erroneous readings. However, recent research has shown that this is not a concern. It is now considered acceptable for sensors to be inserted close to insulin infusion sites.
How can I make inserting the sensor less painful?
Like a pump infusion set, a sensor is inserted under the skin using an introducer needle, which is then removed. As a result, sensor insertion can sometimes be painful. However, there are ways to minimize the pain. One option is to apply ice to the site for approximately 5 minutes before inserting the sensor. Another option is to apply Emla cream (lidocaine 2.5% plus prilocaine 2.5%) one hour before sensor insertion. Apply a pea- or dime-size dollop of cream to the spot where you intend to insert the sensor, then cover it with tape (such as Tegaderm or IV 3000). Wipe the cream off before you insert the sensor.
In all cases, the area should also be cleaned with soap and water or alcohol before sensor insertion, because you are inserting something into the body that is going to stay there for several days. If you use alcohol, be sure to let it dry before inserting the sensor.
What should I do about bleeding at the sensor site?
Bleeding interferes with the ability of the sensor to detect glucose in the interstitial fluid. If there is blood at your sensor site, the glucose readings will be inaccurate or the sensor will not transmit at all.
With a Medtronic CGM system (Guardian REAL-Time or Paradigm REAL-Time Revel), the blood can be mopped up using the corner of a clean tissue or gauze pad: Gently slide the tissue or gauze between the external part of the sensor and your skin. The site may bleed for a few minutes, but as long as you can sop up most traces of blood from the area, the sensor should be OK to use. However, if you get many errors or very inaccurate readings, you should remove that sensor and insert a new one into a different site. Also, if the site keeps bleeding and does not stop, you should remove the sensor and insert a new one in a different location.