Microdialytic monitoring of the cortex during neurovascular surgery

Using microdialysis combined with suitable analytical methods, levels of metabolites in the extracellular fluid of the cerebral cortex were monitored during neurovascular surgery (9 aneurysm and 5 bypass operations). Our aim was to use microdialysis to detect any local ischaemia which could be caused by brain retraction, temporary clipping and dissecting manoevres. For this purpose, parameters were quantified whose levels in the dialysate are known to be influenced by ischaemia (on-line pH, ascorbic acid, uric acid, glutathione, cysteine, glucose, lactate). In the aneurysm series, the on-line pH fell after introduction of the retractor, and rose after removal: also, in many cases, levels of ascorbic acid, glutathione and lactate increased and glucose decreased. These changes are all in accordance with ischaemic conditions in the region of the probe; they disappeared at the end of retraction, or sometimes even before. During the bypass operations, there were no marked changes in on-line pH or in any of the measured parameters. However, in 2 of these patients ascorbic acid, uric acid and glucose levels were very high during the whole measurement, indicating possible changes in metabolism caused by inadequate perfusion (carotid artery stenosis). We conclude that microdialysis is a sensitive method of detecting intraoperative changes in cerebral metabolism.