Effects of microbial invasion on cerebral hemodynamics and oxygenation monitored by near infrared spectroscopy in experimental Escherichia coli meningitis in the newborn piglet

This study was carried out to elucidate the pathophysiologic mechanism of c erebral hyperemia observed during the early phase of bacterial meningitis. We tested the hypothesis that microbial invasion through the blood-brain ba rrier is responsible for cerebral vasodilation and hyperemia in meningitis. Escherichia coli was given either intravenously (i.v.) or intracisternally (i.c.) to closely mimic the primary or secondary bacterial invasion occurr ing in meningitis and newborn piglets were grouped according to their invas ion results (+ or -); 12 in the i.v. (+) group, 14 in the i.v. (-) group, 1 3 in the i.c. (+) group, 15 in the i.c. (-) group. The results were compare d with sight animals in the control group. Near infrared spectroscopy (NIRS ) was employed to monitor changes in total hemoglobin (HbT) oxygenated hemo globin (HbO) deoxygenated hemoglobin (Hb) deduced hemoglobin (HbD) and oxid ized cytochrome aa(3) (Cyt aa(3)). HbT, as an index of cerebral blood volum e, increased progressively in both i.v. (+) and i.v. (-) groups and became significantly different from control and baseline values at 2 h. Hb signifi cantly increased only in i.v. (+) group. HbD, as an index of cerebral blood flow, decreased significantly in i.v. (+), i.v.(-) and i.c. (-) groups and this change was mitigated in i.c. (+)group. HbO was reduced in i.c. (-) gr oup and this decrease was attenuated in i.c. (+) group. increased Cyt aa(3) was observed in all experimental groups after bacterial inoculation. Chang es in ICP, blood pressure, cerebral perfusion pressure, blood or CSF glucos e or lactate, CSF TNF-alpha level, or CSF leukocytes number were not associ ated with changes in NIRS findings. These findings suggest that primary or secondary bacterial invasion across the blood-brain barrier is primarily re sponsible for cerebral vasodilation and hyperemia observed during the early phase of bacterial meningitis.