Regional cerebral blood flow during hyperventilation in patients with acute bacterial meningitis

Mechanical hyperventilation is often instituted in patients with acute bact erial meningitis when increased intracranial pressure is suspected. However , the effect on regional cerebral blood flow (CBF) is unknown. In this stud y, we measured regional CBF (rCBF) in patients with acute bacterial meningi tis before and during short-term hyperventilation. In 17 patients with acut e bacterial meningitis, absolute rCBF (in ml/100 g min(-1)) was measured du ring baseline ventilation and hyperventilation by single-photon emission co mputed tomography (SPECT) using intravenous Xe-133 bolus injection. Intrave nous Tc-99m-HMPAO (hexamethylpropyleneamine oxime) was subsequently given d uring hyperventilation. In 12 healthy volunteers, rCBF was measured by SPEC T and Tc-99m-HMPAO during spontaneous ventilation. Using standard templates to identify regions of interest (ROIs), we calculated rCBF in percentage o f cerebellar (Tc-99m-HMPAO images) or mean hemispheric (Xe-133 images) flow for each ROI, the degree of side-to-side asymmetry for each ROI, and the a nterior-to-posterior flow ratio. On Xe-133 images, absolute rCBF decreased significantly during hyperventilation compared to baseline ventilation in a ll regions, but the relative rCBF did not change significantly from baselin e ventilation (n = 14) to hyperventilation (n = 12), indicating that the pe rfusion distribution was unchanged. On Tc-99m-HMPAO images (n = 12), relati ve rCBF and the anterior-to-posterior flow ratio were significantly lower i n patients than in controls in the frontal and parietal cortex as well as i n the basal ganglia. Focal perfusion abnormalities were present in 10 of 12 patients. Regional cerebral blood flow abnormalities are frequent in patie nts with acute bacterial meningitis. Short-term hyperventilation does not e nhance these abnormalities.