Cgm Trend Data Used To Minimize Postprandial Hyperglycemia And Avoid Hypoglycemia

Patients use the real-time glucose trend data displayed on the hand-held CGM monitor to make more appropriate clinical decisions regarding BG control (20,22,23). The Food and Drug Administration (FDA), however, does not currently allow the patient with diabetes to initiate a change in medical therapy (insulin or oral hypoglycemia medication) based solely upon CGM glucose sensor data. Diabetic patient are therefore required to adjust drug therapy according to traditional SMBG measurements. This limitation was imposed by the FDA to prevent the unsafe administration of insulin, due to the potential for inaccurate CGM sensor data (www.fda.gov).

However, patients given real-time access to CGM glucose sensor information have quickly learned to utilize the trend data to minimize postprandial hyperglycemia and avoid hypoglycemia. Most patients have not required extensive education to utilize the real-time BG data safely and effectively (22-24). In a randomized, prospective clinical trial using the

Postprandial Hyperglycemia Exercise

Time, min

FIGURE 1 Real-time display of frequent BG data (mg/dL), demonstrating rate of glucose rise and fall in relation to meals and exercise, measured using the Metracor VIA-GLU enzyme-based electrochemical sensor.

Time, min

------. i---1----1---1---i----1---r i----1---1---i----1---1-------i----

______.i___j____i___i___j____i___i_ .j____i___i___j____i___i___ j____

------"I---T----1---I---T----1---r 1----1---I---T----1---I----------

______.1___J____I___I___J____I___l_ .J____I___I___J____I___I______J____

SO SO

______.1___J___- J____1___■ J____1 - - / V-1___1___ -1____

FIGURE 1 Real-time display of frequent BG data (mg/dL), demonstrating rate of glucose rise and fall in relation to meals and exercise, measured using the Metracor VIA-GLU enzyme-based electrochemical sensor.

Insulin Pump Catheter
FIGURE 2A DexCom STS Continuous Glucose Monitor attached to the skin of abdomen (left) with sensor tip inserted into the subcutaneous tissue. Insulin pump catheter attached to the skin of abdomen (right) with tip inserted into the subcutaneous tissue.

Medtronic Guardian RT System, patients with type 1 diabetes were able to significantly decrease their HbA1c levels by changing their medications and meals according to real-time glucose trend information. Fifty percent of the patients who used the CGM data continuously for 3 months achieved a significant reduction of HbA1c level > 1%, and 26% achieved reductions > 2% (significantly lower % HbA1c than control group patients, and patients who utilized CGM intermittently) (24). FDA approval should be granted shortly, for patients to utilize real-time CGM glucose sensor information to titrate medical therapy.

FIGURE 2B DexCom STS Continuous Glucose Monitor displaying glucose measurement (194 mg/dL) on y-axis and time (min) on x-axis. Data from patient-worn sensor/transceiver (lower right) is transmitted wirelessly to hand-held monitor with flat-panel display. Monitor is able to display 1, 3, and 9-hour trend data.

Glucose Trend 420 390 360 330 300 270 /dl240 ^210 180 150 120 90 60 30

FIGURE 2C Seventy-two hour glucose profile using the DexCom STS CGM. Note the dynamic nature of glucose fluctuations and relationship between continuous sensor measurements and intermittent SMBG measurements.

Computer algorithms are being developed that analyze glucose sensor data in real-time to diagnose hypoglycemia. The CGM algorithm alerts the patient when the concentration of glucose falls below a programmable threshold (<90, <80, < 70 and < 60 mg/dL) or when the BG levels is predicted to decrease into the hypoglycemia range within the subsequent 20 to 30 min time period (25-27).

Future medical devices may automatically deliver glucagon, glucose or epinephrine to prevent or treat impending or established hypoglycemia. This type of system would be most beneficial to patients who have recurrent hypoglycemia or hypoglycemia unawareness (reduced glucagon and/or epinephrine response to low BG levels). Most clinicians would advocate intensive drug therapy and tight BG control if a CGM system was able to automatically detect and prevent hypoglycemia, prior to the onset of CNS or cardiovascular symptoms (1-8,27).

Algorithms currently being tested in the research setting, utilize glucose trend data and insulin delivery data to minimize hyperglycemia following consumption of a meal. The CGM system algorithms often consider: time since last meal, onset time of current meal, meal size, meal composition, estimated time of gastric emptying/intestinal absorption, time/dose of previously delivered insulin, time/intensity of previous exercise and an estimate of insulin sensitivity (19,20,28-30).

Postprandial hyperglycemia can be minimized by injecting rapid-acting insulin into the subcutaneous (sc) tissue 0 to 20 min before a meal. Moderate hyperglycemia will occur when the insulin bolus is delayed until after the onset of the meal, because of the slow and variable absorption of "rapid" acting insulin from the sc tissue into the circulation (31,32-35). Optimal BG control may be achieved by delivering 60% to 70% of the total meal insulin dose prior to the meal, and 30% to 40% of the total meal insulin dose over the subsequent 2-4 h. CGM algorithms will utilize CGM glucose trend data and an estimate of rapid-acting insulin's pharmacodynamic glucose-lowering effect, to determine the optimal duration of the extended square wave bolus. A meal bolus that is prematurely stopped may lead to postprandial hyperglycemia, while an excessively long meal bolus can lead to hypoglycemia (4,5,20,23,24,28,29,36,37).

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