Relationship between cerebral blood flow and oxygen metabolism, and extracellular glucose and lactate concentrations during middle cerebral artery occlusion and reperfusion:: a microdialysis and positron emission tomography study in nonhuman primates

Object. Changes in lactate and glucose levels in the brain may be used to monitor a dynamic ischemic process. The authors related extracellular concentrations of glucose and lactate to regional cerebral blood flow (rCBF) and cerebral metabolic rate of oxygen (CMRO2) in a model of ischernia. Methods. Transient (2 hours) middle cerebral artery occlusion (MCAO) was performed in eight macaque monkeys. Extracellular measurements of glucose and lactate levels using microdialysis (two probes in each brain) and sequential positron emission tomography measurements were performed during MCAO and reperfusion. Glucose and lactate levels were related to rCBF and CMRO2 as well as the pathophysiological categories of severe ischernia and penumbra. In probe regions characterized by severe ischemia, there were significant changes in glucose and lactate levels and the lactate/glucose ratio. In probe regions distinguished by penumbra, only lactate levels increased significantly and, in general, the changes were smaller and transient. This difference between severe ischemic and penumbral regions was significant for all microdialysis parameters. There was a significant correlation between glucose, and CBF and CMRO2 Lactate concentration was correlated with CMRO2. Conclusions. Extracellular glucose levels might be limited by rCBF, whereas lactate levels were more related to CMRO2. Lactate concentration is a better marker of irreversible ischernia than glucose concentration, although near-zero levels of glucose during MCAO probably signals near-complete cessation of rCBF. In situations with elevated lactate levels, glucose may help to discriminate between partial and severe ischernia.