Intraoperative on-line monitoring of cerebral pH by microdialysis in neurosurgical procedures

The objective of this study was to improve the ability to detect cerebrovascular complications in patients undergoing complicated neurosurgical procedures using on-line monitoring of cerebral pH with in vivo microdialysis. We employed on-line pH monitoring in patients with a variety of neurosurgical procedures including high-flow bypass surgery, aneurysm clipping, and temporal resection in epilepsy treatment. The pH was monitored with a microdialysis probe, usually inserted into the frontal cortex and pH of the dialysate was measured on-line with a pH electrode. We monitored 17 cases: 12 high-flow extracranial-intracranial (EC-IC) bypass procedures, 3 surgeries to clip large basilar tip aneurysms under protection of hypothermic circulatory arrest, and 2 surgeries for intractable seizure disorders. In the patients undergoing high-flow bypass, the pH remained stable in 5 patients and all had an uneventful outcome. In 3 patients, the pH decreased during surgery. One patient had a severe hemiparesis on awaking from anesthesia. The fall in pH in another patient was corrected when the blood pressure was raised during surgery. The pH was also responsive to changes in intraoperative 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 patient This patient awoke with a mild hemiparesis. In the other two patients, the pH was stable during the hypothermia and neither patient had complications. In the patients undergoing temporal lobectomy and hippocampectomy, the pH fell rapidly with the onset of ischemia. We conclude 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 recommended for general use.