Regional Cerebral Blood Flow, Cerebral Metabolic Rate of Oxygen, and Cerebrospinal Fluid Acid‐base Variables in Patients With Acute Meningitis and With Acute Encephalitis

Abstract. Regional cerebral blood flow (rCBF), cerebral metabolic rate of oxygen (CMRO 2 ), jugular venous P o 2 and cerebrospinal fluid (CSF) acid‐base variables have been studied in five patients with meningococcal meningitis, five with pneumococcal meningitis and six with encephalitis. The 133 ‘xenon intra‐arterial injection method was used for the rCBF measurements. The patients were hyperventilating spontaneously. The studies were performed during general anesthesia and artificial ventilation at a Pa co 2 adjusted to the level measured during spontaneous respiration prior to the anesthesia. Average hemispheric CBF was normal and CMRO 2 slightly reduced in patients with meningococcal meningitis. whereas CBF and CMRO 2 were markedly reduced in pneumococcal meningitis and encephalitis. Jugular venous P o 2 was increased (“luxury perfusion”) in meningococcal and pneumococcal meningitis but normal in encephalitis. CSF lactic acid was increased and CSF bicarbonate decreased in all meningitis patients and in some with encephalitis. Functional tests of the rCBF were performed by changes of arterial BP and Pa co 2 ‐ Autoregulation (rCBF is normally independent of the BP within wide limits) was frequently impaired, whereas the response to Pa co 2 changes was preserved in most cases (rCBF normally increases with increased Pa co 2 ). Focal rCBF abnormalities as disclosed in the control condition or during the functional tests were infrequent in meningitis but frequent in encephalitis. The results suggest that the brain of these patients is vulnerable to factors such as hypertension, hypercapnia and hypoxia. A more deliberate use of sedatives combined with artificial hyperventilation is advocated. Epileptic seizures should be counteracted by all available means.