Intracerebral microdialysis in neurosurgical intensive care patients utilising catheters with different molecular cut-off (20 and 100 kD)

Objective. To compare the properties of a new intracerebral micro-dialysis catheter with a high cut-off membrane (molecular cut-off 100kDalton) with a standard catheter (CMA70, molecular cut-off 20kDalton). Methods. Paired 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 (20mm) and cut-off properties of the catheter membranes (100kDalton) 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). Results. Fluid 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. Conclusion. Microdialysis 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.