SIMULTANEOUS INTRACEREBRAL MICRODIALYSIS AND POSITRON EMISSION TOMOGRAPHY IN THE DETECTION OF ISCHEMIA IN PATIENTS WITH SUBARACHNOID HEMORRHAGE

Intracerebral microdialysis (MD) was applied in patients with subarach noid hemorrhage. The regional CBF, the CMRO(2), and oxygen extraction ratio (OER) were measured with simultaneous positron emission tomograp hy (PET). The aim was to directly correlate alterations in dialysate l evels of energy-related metabolites (lactate, lactate/pyruvate ratio, hypoxanthine) and excitatory amino acids (EAAs) (glutamate and asparta te) to the energy state in the MD probe region as determined by PET. R egional ischemia was defined according to Heiss et al. and Lassen (Hei ss et al., 1992; Lassen, 1966). Whole-brain ischemia was considered pr esent when the OER for the whole brain exceeded the mean whole-brain O ER + 2 SD of six reference patients. In general, the presence of whole -brain ischemia and/or regional ischemia within the region of the MD p robe was associated with increased levels of energy-related metabolite s and EAAs retrieved by MD. Increased levels of energy-related metabol ites and EAAs were only occasionally seen when PET did not show any si gns of ischemia or when signs of regional ischemia were found remote f rom the MD probe region, Thus, the energy-related metabolites and EAAs may be used as extracellular ''markers'' of ischemia. PET may be of u se in defining critical ischemic regions (tissue at risk) where the MD probe can be inserted for chemical monitoring.