Regional ischemia during cerebral bypass surgery

Abstract

We evaluated brain tissue oxygen pressure (PO2), carbon dioxide pressure (PCO2), and pH during regional ischemia produced by temporary brain artery occlusion. This 45-year-old woman with cerebral occlusive disease was scheduled for right superficial temporal artery (STA) to middle cerebral artery (MCA) bypass. Two Paratrend 7 sensors measuring PO2, PCO2, and pH were inserted into the cortex in the distribution of the MCA at a distance of 1 cm from each other. Jugular bulb oxygen saturation was measured by oximetry. Local perfusion was measured with a flow probe on the MCA and using a laser Doppler. Tissue responses were recorded during: (1) 100% oxygen ventilation, (2) hypercapnia, and (3) an 18 minute occlusion of the right MCA. Under baseline conditions, tissue PO2, PCO2, and pH suggested that ischemia was present in tissue measured by both sensors. Tissue PO2 rose 40%-50% in both regions during 100% oxygen ventilation. During hypercapnia, blood flow increased in the MCA, but local perfusion did not increase in region 2. During temporary occlusion of the MCA, ischemic changes in PO2, PCO2, and pH were seen in region 2 but not in region 1. Local perfusion decreased 80% in region 2, where ischemic changes were seen. These results show that changes in tissue PO2, PCO2, and pH are consistent with local perfusion. The use of multiple tissue sensors can detect the presence of watershed ischemia that is not demonstrated by jugular bulb measurement.