Page 149 - Glucose Monitoring Devices

150 CHAPTER 7 Clinical impact of CGM use

Senseonics
The Eversense is the first implantable CGM system promising a sensor life span of
180 days and an 8.8% MARD. The small long-term sensor requires professional
insertion within the subcutaneous space and is wirelessly powered by an externally
worn smart transmitter. Real-time glucose levels, trends, and predictive alerts are
transmitted to the mobile app via Bluetooth technology. Nondirect contact commu-
nication between the implanted sensor and external transmitter permits the removal
or changing of the smart transmitter without the need to reinsert a new sensor.
Additional benefits of an implanted sensor include being able to partake in activities
requiring submersion in water for long periods. The practical benefits extend to the
smart transmitter that is rechargeable, water-resistant, submerged in 1 m for 30 min,
and capable of delivering on-body vibration alerts to notify hypo and hyperglycemia
even when separated from the smartphone receiver.

Flash glucose monitoring
Flash glucose monitoring, also called as intermittent CGM, is a subset of CGM
where glucose levels are reported only after the user scans the device by closely
passing the Freestyle Libre reader or a smartphone with the Freestyle Librelink
App over the sensor. In addition to presenting the current glucose value to the smart-
phone or card device, sensor scanning also displays the last 8 h of glucose data and a
trend arrow to represent the current glucose direction. Similar to CGM, both tech-
nologies use enzyme electrode technology to measure changes in interstitial fluid
glucose and require the user to wear a subcutaneously sited sensor. Flash sensors
have a life span of 14 days and are factory calibrated overcoming the need to
perform twice-daily steady-state capillary glucose calibration. This is a welcomed
feature for users looking to minimize fingerprick testing; however, it can potentially
result in “sensor drift” disparity toward the end of the sensor life cycle. Different
from CGM where 5-min interval glucose levels are continuously being uploaded
and saved for detailed retrospective analysis, flash sensors store readings every
15 min, and retrospective analysis is limited to the last 8 h. The absence of a contin-
uous glucose data stream precludes the application of flash glucose monitoring in the
sensor-augmented pump and artificial pancreas systems. Alarm notification of hypo-
and hyperglycemia is another significant CGM feature not present in flash glucose
monitoring systems. The exclusion of this feature relies on the user to scan the
sensor when hypoglycemia is suspected and could lead to missed events, particularly
among individuals with diminished hypoglycemia awareness.
Randomized controlled trials in T1DM and T2DM have reported reduced inci-
dence of hypoglycemia when flash glucose monitoring is applied as an adjunct along-
side SMBG [68,69]. The IMPACT trial demonstrated a greater reduction in the
incidence, magnitude, and time spent in hypoglycemia (<70 mg/dL, <3.9 mmol/L)
after 6 months of using flash monitoring in well-controlled adults with T1DM [68].