Continuous glucose monitoring for intensive care patients using whole blood microdialysis

Introduction

The objective of this study was to investigate whether continuous glucose monitoring for intensive care patients could be implemented using blood microdialysis (MD) as tight glycaemic control reduces mortality and morbidity of critically ill patients. Currently investigated is whether the subcutaneous tissue is an adequate and representative site for glucose monitoring. We have designed and tested a novel system that allows continuous measurement of glucose concentration in whole blood based on MD.

Methods

Na-heparin is pumped to the tip of a double lumen catheter and the blood–heparin mixture is withdrawn continuously at a mixing ratio of 1:1 at a flow of 4 ml/hour. The blood–heparin mixture is microdialysed in a planar flow-through MD unit and is discarded thereafter. The dialysate is collected and analysed for glucose concentration via Beckman analysis and referred to venous blood samples taken from the reference arm. Eight healthy volunteers underwent a 12-hour investigation including an OGTT. Glucose readings from dialysate and venous blood were obtained in a 15–30 minute interval.

Results

All eight subjects successfully completed the 12-hour trial. The coefficient of correlation between continuously withdrawn microdialysed blood and venously taken reference blood samples was r = 0.9834 (0.9753–0.9958). The Clark Error Grid Analysis (EGA) revealed that 99.5% of all data pairs are in the A range (220 of 221). Applying the novel Insulin Titration EGA yielded in 100% of data pairs the 'acceptable treatment' area.

Conclusion

Blood MD based on continuous blood withdrawal and extracorporeal MD is a promising approach to obtain dialysate reliably, safely and continuously for long-term determination of blood glucose concentration with online sensors. The correlation between glucose concentration of dialysate and reference venous blood samples is excellent. The patency of the double lumen catheter in the current form could be improved by introducing adequate flushing sequences or by using it with central lines. Further long-term studies are necessary to test the system together with online sensors.