Numerical and clinical accuracy of a continuous glucose monitoring system during intravenous insulin therapy in the surgical and burn intensive care units

Abstract

Background: Intensive insulin therapy (IIT) for glycemic control in critically ill patients has been shown to be beneficial. Continuous glucose monitoring systems (CGMSs) have been approved as an adjunct to complement standard glucose monitoring in type 2 diabetes mellitus. This study was designed to evaluate the accuracy of a real-time CGMS (DexCom STS) in the intensive care unit (ICU). We also evaluated its reliability and accuracy using a hyperinsulinemic-euglycemic and a hyperglycemic clamp study.

Methods: Nineteen patients were enrolled in this 7-day study [13 = surgical intensive care unit (SICU), 6 = burn intensive care unit (BICU)]. The patients were on IIT for at least 2 h prior the subcutaneous sensor insertion. Mean age and body mass index for SICU and BICU patients were 60.3 +/- 3.7 and 64.5 +/- 6.2 years and 36.6 +/- 5.0 and 33.85 +/- 3.4 kg/m2, respectively. DexCom accuracy was analyzed separately for the Johnson & Johnson (J&J) calibration finger sticks, Roche Accucheck finger sticks, and the Hitachi 917 analyzer measurements on serum using Clarke error grid analysis and Bland-Altman analysis. In the clamp studies, 20 patients were enrolled, and the data were analyzed similarly.

Results: There were 1065 pairs of DexCom-Accucheck, 232 pairs of DexCom-J&J, and 84 pairs of DexCom-Hitachi in ICU patients. For DexCom-Accucheck, 68.26% of the pairs fell into zone A, 31.83% into zone B, and 0.75% into zone C. There were no values in zones D or E. From the 1102 matching DexCom-Beckman pairs in clamp studies, 42.29% were in zone A, 55.90% were in zone B, and 4.08% were in zone C.

Conclusions: Despite the high percentage of measurements in zones A and B, underestimation of hypoglycemia by DexCom measurements makes it an unreliable device in the ICU setting.

Figure 1.

Mean 6 h blood glucose values over a 7-day study course for 19 ICU patients. Closed circles represent Accucheck glucometer measurements, and open circles represent DexCom values.

Figure 2.

Blood glucose measurements for an ICU patient. Tylenol administration was recorded at two different time points. Open circles represent DexCom, open triangles represent Accucheck, crosses represent the J&J glucometer, and closed diamonds represent the Hitachi analyzer.

Figure 3.

Scatter plot of DexCom–Accucheck blood glucose pairs using point EGA.

Figure 4.

Scatter plot of DexCom–J&J glucometer blood glucose pairs using point EGA.

Figure 5.

Scatter plot of DexCom–Hitachi blood glucose pairs using point EGA.

Figure 6.

Bland–Altman plot of blood glucose measurements from Accucheck and DexCom. The solid line represents the MD, and the dashed line represents ±2 SD. The top, middle, and lower panels represent hypoglycemic, normoglycemic, and hyperglycemic regions, respectively.

Figure 7.

Mean 5 min plasma and blood glucose values over a 330 min clamp study for 20 patients. Closed circles represent Beckman plasma measurements, and open circles represent DexCom blood glucose values.

Figure 8.

Plasma and blood glucose measurements for a clamp study. Open circles represent DexCom, closed circles represent Beckman, and stars represent the J&J glucometer. Note that, from 60–90, 139–150, and 185–200 min, there were no glucose values detected by DexCom.

Figure 9.

Scatter plot of DexCom–Beckman blood glucose pairs using point EGA.

Figure 10.

Bland–Altman plot of plasma glucose measurements from Beckman and blood glucose measurements from DexCom. The solid line represents the MD, and the dashed line represents ±2 SD. The top, middle, and lower panels represent hypoglycemic, normoglycemic, and hyperglycemic regions, respectively.