Bedside microdialysis reflects dysfunction of cerebral energy metabolism in patients with aneurysmal subarachnoid hemorrhage as confirmed by 15O-H2O-PET and 18F-FDG-PET

Objective: To compare microdialysis (MD) and positron emission tomography (PET) in the detection of ischemia in aneurysmal subarachnoid hemorrhage (SAH) patients. Methods: 15 SAH patients (13F/2M, 48 +/- 13 years, WFNS Grade I-V) were prospectively included in the study. A MD-catheter was inserted into the brain parenchyma most likely to be affected by vasospasm directly after aneurysm clipping. Glucose, pyruvate, lactate, glutamate and glycerol were analyzed hourly (CMA 600). O-15-H2O-PET scans (n=10) and F-18-FDG-PET scans (n=13) were performed between the day 2 and 17 after SAH. O-15-H2O-PET data were merged with CT scans to provide quantification of rCBF within the MD-ROI (rCBF(MD); Amira, ZIB Berlin, Germany). F-18-FDG-PET data were evaluated visually by visual analysis. Results: Regions of glucose hypometabolism were observed in 10 patients with symptoms of ischemia. Their rCBF was lower compared to asymptomatic patients (p < 0.05). The MD levels of glutamate, lactate, the L/P ratio and glycerol were significantly higher in symptomatic than asymptomatic patients (p < 0.05). Out of all measured MD parameters, glutamate showed the closest correlation with rCBF (r=-0.66, p=0.014). Microdialysis parameters were well correlated with glucose hypometabolism (F-18-FDG-PET) and symptoms of ischemia. However, the threshold for a metabolic derangement was above the limits of cerebral ischemia defined by PET. Conclusion: MD is a useful tool to monitor ischemia, especially in patients with high-grade SAH.