Accuracy of Intra-arterial and Subcutaneous Continuous Glucose Monitoring in Postoperative Cardiac Surgery Patients in the ICU

Abstract

Background: The GluCath® intra-arterial continuous glucose monitoring (IA-CGM) system uses a novel quenched chemical fluorescence sensing mechanism to optically measure blood glucose when deployed in the radial artery. The aim of this study was to compare the accuracy of the IA-CGM and the FreeStyle Navigator® subcutaneous continuous glucose monitoring (SC-CGM) system with standard care.

Methods: After admission to the intensive care unit (ICU), the IA-CGM was inserted via a 20 gauge radial arterial study catheter and the SC-CGM was placed at the abdominal wall of postoperative cardiac surgery patients with an expected ICU length of stay > 24 hours. Each device was calibrated according to manufacturer instructions. Glucose values of both CGM systems were blinded for the clinical staff. Reference blood glucose samples were collected from the study catheter every 1-2 hours for at least 24 hours and analyzed on a Radiometer ABL blood gas analyzer.

Results: The IA-CGM and SC-CGM sensors were successfully inserted in 8 subjects. Accuracy assessment was performed with 183 paired points: 85.8% of the IA-CGM measurements and 84.2% of the SC-CGM measurements met ISO 15197:2003 glucometer criteria (within 20%) across a 79-248 mg/dl (4.4-13.8 mmol/L) glucose range. Overall ± SD mean absolute relative difference was 12.3 ± 11.3% for IA-CGM and 11.1 ± 8.3% for SC-CGM (difference -1.2%, 95% CI -3.3 to 0.8; P = .24).

Conclusions: The IA-CGM system directly measured arterial blood glucose and did not interfere with clinical care. However, accuracy was similar to that of the less invasive SC-CGM device.

Keywords: accuracy; continuous monitoring; glucose; intra-arterial; subcutaneous; vascular.

Figure 1.

ISO-modified Bland–Altman plots for the (A) GluCath IA-CGM system and (B) FreeStyle SC CGM system. The x-axis represents the average of sensor and reference glucose measurements in mg/dl. The y-axis represents the absolute difference between sensor and reference glucose measurements in mg/dl. The solid line represents the mean difference (GluCath −8.6 and FreeStyle −8.0 mg/dl); dotted lines are drawn at the mean difference ± 1.96 times the standard deviation of the mean difference. The long dashed lines represent the ISO-15197:2003 criteria.