Continuous glucose monitoring by intravenous microdialysis: influence of membrane length and dialysis flow rate.
BACKGROUND
The benefit of tight glucose control in the intensive care unit is controversial. Part of the debate is around the frequency of glucose measurements, and therefore, a continuous glucose monitoring system is needed. Previously, we have shown that intravenous microdialysis has the potential for this purpose but that the accuracy must be improved. The aim of this study was to investigate the effects of the microdialysis membrane length and the perfusion rate on improving the accuracy.


METHODS
Two volunteer studies were performed, one comparing intravenous microdialysis catheters with different lengths (10 and 20 mm) and one comparing different perfusion rates (0.5, 1 and 2 μl/min) with plasma glucose reference levels. Median values of seven samples taken over 70-min periods were compared using Bland-Altman plots.


RESULTS
When microdialysis membranes of 10 and 20 mm perfused at a rate of 1 μl/min were used, the differences with measured plasma glucose levels were 30% ± 21% and 14% ± 13%. In comparison, plasma glucose measured in two different veins gave a difference of 3% ± 3%. In the second study, the differences between measured plasma glucose and that estimated with a microdialysis membrane of 30 mm perfused at 0.5, 1 and 2 μl/min were 8% ± 7%, 25% ± 19% and 39% ± 28%. Bland-Altman analyses gave the best line of equality (-0.11 mM) and the lowest limits of agreement (1.13 and -1.35 mM) when using the 30-mm membrane perfused with 0.5 μl/min.


CONCLUSIONS
The agreement of the intravenous microdialysis with plasma glucose levels improved significantly when increasing the microdialysis membrane length, and thereby the membrane area, and decreasing the perfusion rate.
Department of Anesthesiology and Intensive Care Medicine, Karolinska University Hospital, Huddinge, Sweden.
O
O
Rooyackers
C
C
Blixt
P
P
Mattsson
J
J
Wernerman
D001786:Blood Glucose / Q000032:analysis*; D015314:Dialysis Solutions; D006801:Humans; D007362:Intensive Care Units; D008567:Membranes, Artificial; D017551:Microdialysis / Q000295:instrumentation* / Q000379:methods*; D008991:Monitoring, Physiologic; D010477:Perfusion; D006435:Renal Dialysis
D001786:Blood Glucose; D015314:Dialysis Solutions; D008567:Membranes, Artificial