Brain tissue oxygen pressure, carbon dioxide pressure, and pH during hypothermic circulatory arrest

BACKGROUND This study evaluated brain tissue oxygen pressure (PO2), carbon dioxide pressure (PCO2), and pH in a patient during hypothermic circulatory arrest. METHODS A combined PO2, PCO2, and pH sensor was placed in cortex tissue. Brain temperature was then decreased to 17 degrees C followed by circulatory arrest for 44 minutes during an endarterectomy of the M1 segment of the middle cerebral artery. RESULTS Brain tissue PO2 increased during brain cooling from 10 mmHg-30 mmHg and decreased to zero following exsanguination. During circulatory arrest, tissue PCO2 increased to >200 mmHg and pH decreased to 6.0. Tissue PCO2 and pH recovered during circulatory rewarming but the increase in PO2 was delayed. Tissue parameters continued to improve during 2 days of postsurgical monitoring and were correlated with neurologic recovery. CONCLUSIONS These results show that brain tissue PO2, PCO2, and pH measures indicate the severity of ischemia during hypothermic cardiac arrest and recovery in the postoperative period.