A combined microdialysis and FDG-PET study of glucose metabolism in head injury

Microdialysis continuously monitors the chemistry of a small focal volume of the cerebral extracellular space. Positron emission tomography (PET) establishes metabolism of the whole brain but only for the scan's duration. This study's objective was to apply these techniques together, in patients with traumatic brain injury, to assess the relationship between microdialysis (extracellular glucose, lactate, pyruvate, and the lactate/pyruvate (L/P) ratio as a marker of anaerobic metabolism) and PET parameters of glucose metabolism using the glucose analogue [F-18]-fluorodeoxyglucose (FDG). In particular, we aimed to determine the fate of glucose in terms of differential metabolism to pyruvate and lactate. Microdialysis catheters (CMA70 or CMA71) were inserted into the cerebral cortex of 17 patients with major head injury. Microdialysis was performed during FDG-PET scans with regions of interest for PET analysis defined by the location of the gold-tipped microdialysis catheter. Microdialysate analysis was performed on a CMA600 analyser. There was significant linear relationship between the PET-derived parameter of glucose metabolism (regional cerebral metabolic rate of glucose; CMRglc) and levels of lactate (r = 0.778, p < 0.0001) and pyruvate (r = 0.799, p < 0.0001), but not with the L/P ratio. The results suggest that in this population of patients, glucose was metabolised to both lactate and pyruvate, but was not associated with an increase in the L/P ratio. This suggests an increase in glucose metabolism to both lactate and pyruvate, as opposed to a shift towards anaerobic metabolism.