INTRAOPERATIVE ONLINE MONITORING OF CEREBRAL PH BY MICRODIALYSIS IN NEUROSURGICAL PROCEDURES

The objective of this study was to improve the ability to detect cereb rovascular complications in patients undergoing complicated neurosurgi cal procedures using on-line monitoring of cerebral pH with in vivo mi crodialysis. We employed on-line pH monitoring in patients with a vari ety of neurosurgical procedures including high-flow bypass surgery, an eurysm clipping, and temporal resection in epilepsy treatment. The pH was monitored with a microdialysis probe, usually inserted into the fr ontal cortex and pH of the dialysate was measured on-line with a pH el ectrode. We monitored 17 cases: 12 high-flow extracranial-intracranial (EC-IC) bypass procedures, 3 surgeries to clip large basilar tip aneu rysms under protection of hypothermic circulatory arrest, and 2 surger ies for intractable seizure disorders. In the patients undergoing high -flow bypass, the pH remained stable in 5 patients and all had an unev entful outcome. In 3 patients, the pH decreased during surgery. One pa tient had a severe hemiparesis on awaking from anesthesia. The fall in pH in another patient was corrected when the blood pressure was raise d during surgery. The pH was also responsive to changes in intraoperat ive ventilation and probably also to brain edema with elevation of pH values. In the three patients undergoing basilar tip aneurysm clipping under hypothermic circulatory arrest, the pH fell to 6.41 in one pati ent This patient awoke with a mild hemiparesis. In the other two patie nts, the pH was stable during the hypothermia and neither patient had complications. In the patients undergoing temporal lobectomy and hippo campectomy, the pH fell rapidly with the onset of ischemia. We conclud e that it is possible to monitor the cerebral extracellular pH with on -line microdialysis. The information obtained may alert the surgeon to the possibility of impending cerebral ischemia or other complications . However, further experience is needed before the technique can be re commended for general use.