Continuous on-line glucose measurement by microdialysis in a central vein. A pilot study

Introduction: Tight glucose control in the ICU has been proven difficult with an increased risk for hypoglycaemic episodes. Also the variability of glucose may have an impact on morbidity. An accurate and feasible on-line/continuous measurement is therefore desired. In this study a central vein catheter with a microdialysis membrane in combination with an on-line analyzer for continuous monitoring of circulating glucose and lactate by the central route was tested. Methods: A total of 10 patients scheduled for major upper abdominal surgery were included in this observational prospective study at a university hospital. The patients received an extra central venous catheter with a microdialysis membrane placed in the right jugular vein. Continuous microdialysis measurement proceeded for 20 hours and on-line values were recorded every minute. Reference arterial plasma glucose and blood lactate samples were collected every hour. Results: Mean microdialysis-glucose during measurements was 9.8 +/- 2.4mmol/l.No statistical difference in the readings was seen using a single calibration compared to eighth hour calibration (P = 0.09; t-test). There was a close agreement between the continuous reading and the reference plasma glucose values with an absolute difference of 0.6 +/- 0.8mmol, or 6.8 +/- 9.3% and measurements showed high correlation to plasma readings (r = 0.92). Thelimit of agreement was 23.0%(1.94 mmol/l) compared to arterial plasma values with a line of equality close to zero. However, in a Clarke-Error Grid 93.3% of the values are in the A-area, and the remaining part in the B-area. Mean microdialysis-lactate was 1.3 +/- 1.1mmol/l. The measurements showed high correlation to the blood readings (r = 0.93). Conclusion: Continuous on-line microdialysis glucose measurement in a central vein is a potential useful technique for continuous glucose monitoring in critically ill patients, but more improvements and testingare needed.