Table 2.
Metrics to report glycemic control using continuous glucose monitoring systems
| 1. Measures of central tendency |
| a. Mean blood glucose per patient, per day of ICU stay and during whole stay in the ICU |
| b. For populations of patients, the median and interquartile range of individual patient means should be reported |
| c. For comparison of glycemic control achieved with intermittent measurement versus continuous measurement, two groups should be studied in a randomized controlled trial, both groups should have blood glucose concentration recorded by a CGM but the output of the CGM should be masked in the control group where blood glucose concentration is managed using intermittent measurement of blood glucose concentration |
| 2. Measures of variability and dispersion |
| a. Standard deviation and coefficient of variation of blood glucose (for comparison of glycemic control with intermittent measurement, two groups should be studied - both groups should have blood glucose concentration recorded by a CGM but the output of the CGM be masked in the group where the blood glucose concentration is managed using intermittent measurement of blood glucose concentration) |
| b. Peak blood glucose concentration reached within a set time period after correction of hypoglycemia |
| c. Analysis of the rate of change of the blood glucose concentration |
| 3. Hypoglycemia and lowest blood glucose concentration |
| a. Lowest blood glucose concentration recorded per patient |
| b. Number of times a blood glucose concentration defining hypoglycemia or severe hypoglycemia was recorded |
| c. Area above the curve under the target for mild and severe hypoglycemia |
| d. Duration of time with blood glucose below the concentration defining hypoglycemia or severe hypoglycemia |
| 4. Range and exposure measures |
| a. Percentage of time the blood glucose concentration is in the target range |
| b. Percentage of time the blood glucose concentration is outside a nominated target range |
| c. Area under the curve above the upper target for hyperglycemia |
| d. Area above the curve but under the target for mild and severe hypoglycemia |
| Desirable performance standards for continuous glucose monitoring systems - the meeting accepted that these were desirable performance standards that might not be currently achievable |
| There was acceptance but not complete agreement that desirable point accuracy might vary depending on whether CGMs were intended to operate alone and be used to adjust insulin dosing or be used to only as a warning system to advise clinicians when to check blood glucose on a reference system |
| 1. Desirable features with regard to set-up, calibration and integration with standard ICU care |
| a. <20 minutes to set by a nurse, technician, or physician |
| b. <10 minutes required for initial and subsequent calibration |
| c. <20 minutes required for sensor insertion |
| d. Calibration against a reference standard to maintain point accuracy is required no more frequently than every 8 hours and preferably no more than twice per 24 hours |
| e. CGM requires few nursing interventions per 24 hours to produce a near-continuous glucose datastream |
| f. CGM sensor inserted into an arterial or central venous catheter should not adversely affect blood sampling or monitoring of cardiovascular system or increase the frequency with which such monitoring lines occlude |
| g. Incidence infection, hematoma, tissue ischemia, and/or thromboembolism should not exceed that which occurs in usual clinical practice in the absence of a CGM |
| 2. Desirable reliability |
| a. CGM should continuously measure glucose and display in real time >95% of the time for the duration of time specified in the product label (2 to 7 days) |
| b. Skips in data acquisition due to system faults or failures should not exceed 30 minutes at a time (data may be missing for other reasons; for example, patient transports) |
| c. The CGM should have an internal mechanism that prevents the display or reporting of erroneous or spurious data |
| 3, Desirable point accuracy - this should be the same as for intermittent monitors if the CGM is being used alone to guide clinical management and administration of insulin |
| a. 98% of readings should be within 12.5% of a reference standard (or within 0.55 mmol/l for readings <5.5 mmol/l; the remaining 2% of readings should be within 20% of a reference standard |
| b. CGM sensors inserted in arterial and central venous catheters may transiently indicate false low readings when those catheters are flushed with saline or other glucose-free solutions. The CGM should alert the treating clinicians that rapid reductions in the measured blood glucose concentration may be due to flushing of the arterial or central venous catheter |
| c. CGM sensors inserted in peripheral and central veins may transiently indicate false high readings if venous blood in those veins is contaminated with glucose-containing solutions. The CGM should alert the treating clinicians to rapid increases in the measured blood glucose concentration that may be due to contamination by glucose-containing solutions |
| 4. Rate or trend accuracy - CGMs should be carefully characterized in the intended-use critical care patient population to ensure point accuracy over a wide range of blood glucose rates of change. Rate or trend metrics have not been tested sufficiently to provide definitive guidance |
| 5. Alarms and alerts for hypoglycemia and hyperglycemia alerts |
| a. Real-time blood glucose concentration and trend data should be displayed at the bedside; with visual and audible alerts and alarms for hypoglycemia, hyperglycemia, and rapid rates of change |
| b. The CGM data should be sufficiently frequent, reliable, and accurate for alarm algorithms to detect and/or predict hypoglycemia and hyperglycemia with high sensitivity and specificity |
The meeting recognized that further research is needed to determine which of these metrics are closely associated with mortality and major morbidity when continuous or automated intermittent glucose monitoring systems (CGMs) are used.