• J Hillman, P Milos, Z Q Yu, F Sjögren, C Anderson, and P Mellergård.
• Department of Neurosurgery, University Hospital, Linköping, Sweden.
• Acta Neurochir (Wien). 2006 Mar 1;148(3):319-24; discussion 324.

ObjectiveTo compare the properties of a new intracerebral micro-dialysis catheter with a high cut-off membrane (molecular cut-off 100 kDalton) with a standard catheter (CMA70, molecular cut-off 20 kDalton).MethodsPaired intracerebral microdialysis catheters were inserted in fifteen comatose patients treated in a neurosurgical intensive care unit following subarachnoid haemorrhage or traumatic brain injury. The high-cut-off catheter (D(100)) differed from the CMA 70 catheter by the length (20 mm) and cut-off properties of the catheter membranes (100 kDalton) and the perfusion fluids used (Ringer-Dextran 60). Samples were collected every 4-6 hours, analyzed bedside (for glucose, glutamate, glycerol, lactate, pyruvate and urea) and later in the laboratory (for total protein).ResultsFluid recovery was similar for the two types of catheters, but significantly more protein was recovered by the D(100) catheter. The recovery of glycerol and pyruvate did not differ, while minor differences in recovery of glutamate and glucose were observed. The recovery of lactate was considerably lower in the D(100) catheter (p < 0.01), influencing the lactate/pyruvate-ratio. The patterns of concentration changes over time were consistent for all metabolites, and independent of type of catheter.ConclusionMicrodialysis catheters with high cut-off membranes can be used in routine clinical practice in the NSICU, adding the possibility of macro-molecule sampling from the extracellular space during monitoring.

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