Accuracy of a Novel Noninvasive Transdermal Continuous Glucose Monitor in Critically Ill Patients

Abstract

Stress hyperglycemia and hypoglycemia are associated with increased morbidity and mortality in the critically ill. Intermittent, random blood glucose (BG) measurements can miss episodes of hyper-and hypoglycemia. The purpose of this study was to determine the accuracy of the Symphony® continuous glucose monitor (CGM) in critically ill cardiac surgery patients. Fifteen adult cardiac surgery patients were evaluated immediately postoperatively in the intensive care unit. Prelude® SkinPrep prepared the skin and a sensor was applied to 2 test sites on each subject to monitor interstitial fluid glucose. Reference BG was sampled at 30-to 60-minute intervals. The skin at the test sites was inspected for adverse effects. Accuracy of the retrospectively analyzed CGM data relative to reference BG values was determined using continuous glucose-error grid analysis (CG-EGA) and mean absolute relative difference (MARD). Using 570 Symphony CGM glucose readings paired with reference BG measurements, CG-EGA showed that 99.6% of the readings were within zones A and B. BG measurements ranged from 73 to 251 mg/dL. The MARD was 12.3%. No adverse device effects were reported. The Symphony CGM system is able to safely, continuously, and noninvasively monitor glucose in the transdermal interstitial fluid of cardiac surgery intensive care unit patients with accuracy similar to that reported with other CGM systems. Future versions of the system will need real-time data analysis, fast warm-up, and less frequent calibrations to be used in the clinical setting.

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“…Symphony's glucose sensor does not need to be inserted into the patient and, thus, does not give rise to the risks or discomfort associated with needle-based CGM systems. Symphony will provide continuous access to glucose values and changes and should identify prolonged excursions into the hyperglycemic and hypoglycemic zones [15].…”

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“…Further analysis of MARD between the reference and CGM values revealed correlation at 11.0% MARD overall, which is in the middle of the range reported by similar studies that have shown an MARD of 7%-15%. 10,36,37 Segmented analysis of MARD as a function of reference glucose showed very large MARD in the hypoglycemia range, although relatively few values were used to make this determination. Analysis of MARD by rate of change of sensor glucose showed large MARD for rapidly falling BG, but surprisingly good values for flat and even rapidly rising sensor glucose values.…”

“…Saur et al also investigated CGM after cardiac surgery using the Symphony CGM system and found 99.6% of readings in Zones A and B with an MARD of 12.3%. 10 39 Their study used only three calibrations per day. Overall, the findings from this study reveal similar MARD and Zone A and B percentages although with a higher calibration frequency than other recent studies.…”

“…8,9 Usual care for postsurgical, critically ill, and post-transplant patients is to obtain intermittent glucometer whole blood glucose (BG) values every 1-4 h depending on the acuteness of their condition and the clinical protocol. 10,11 With continued refinement, improvement, and clinical acceptance of continuous glucose monitoring (CGM) systems, these populations may stand to benefit from ascertainment of continuous rather than intermittent BG values. [10][11][12] CGM systems measure interstitial fluid glucose concentrations through subcutaneously placed glucose-sensing probes operating with a glucose-oxidase enzyme-based technology that is similar to the operation of glucometers.…”

“…10,11 With continued refinement, improvement, and clinical acceptance of continuous glucose monitoring (CGM) systems, these populations may stand to benefit from ascertainment of continuous rather than intermittent BG values. [10][11][12] CGM systems measure interstitial fluid glucose concentrations through subcutaneously placed glucose-sensing probes operating with a glucose-oxidase enzyme-based technology that is similar to the operation of glucometers. 13,14 Current commercially available devices require calibration against concurrent BG values, based on the assumption that glucose concentration in the interstitial fluid is directly related to BG concentration and that this relationship is stable.…”