Measurement of ischemia by changes in tissue oxygen, carbon dioxide, and pH

Abstract

BACKGROUND We evaluated the ability of brain tissue oxygen pressure (PO 2), carbon dioxide pressure (PCO 2), and pH to detect regional ischemia produced by temporary brain artery occlusion, compared with a group without artery occlusion. METHODS Patients undergoing craniotomy for cerebrovascular surgery were recruited for this study. A 0.5-mm-diameter probe was inserted into brain tissue to measure PO 2, PCO 2, and pH continuously. Group 1 ( n = 15) did not receive brain artery occlusion during their surgical procedure. In Group 2, brain artery occlusion was produced for aneurysm clipping ( n = 10) or extracerebral to intracerebral artery bypass ( n = 3). Mean arterial pressure was maintained above 90 mmHg in both groups. Measurements were made after artery occlusion or sham treatment and compared with baseline. RESULTS Under baseline conditions, tissue PO 2, PCO 2, and pH were not different between the groups. In Group 2, brain artery occlusion for a median time of 7 minutes (range, 2–48 min) significantly decreased PO 2 and pH and increased PCO 2 compared with baseline. There were no significant changes in Group 1. During artery occlusion, PO 2 decreased below 10 mmHg and/or pH decreased below 7.0 in 8 of 13 patients. CONCLUSIONS Regional brain ischemia can be consistently detected and treated by monitoring tissue metabolism. It will be necessary in the future to identify critical levels and duration of decreases in PO 2 and pH that lead to irreversible neuronal injury.