Treatment with moderate hypothermia for 24 hours in patients with severe traumatic brain injury and coma scores of 5 to 7 on admission hastened neurologic recovery and may have improved the outcome.
Cerebral blood flow (CBF) measurements were made in 75 adult patients with closed head injuries (mean Glasgow Coma Scale score 6.2) using the xenon-133 intravenous injection method with eight detectors over each hemisphere. All patients were studied acutely within 96 hours of trauma, and repeatedly observed until death or recovery (total of 361 examinations). Arteriojugular venous oxygen differences (AVDO2) were obtained in 55 of the patients, which permitted assessment of the balance between metabolism and blood flow, and provided estimates of cerebral metabolic rate for oxygen (CMRO2). Based on mean regional CBF, the patients were classified into two groups: those who exhibited hyperemia on one or more examinations, and those who had a consistently reduced flow during their acute illness. "Hyperemia" was defined as a normal or supernormal CBF in the presence of coma, a definition that was independently confirmed by narrow AVDO2's indicative of "luxury perfusion". During coma, all patients showed a significant depression in CMRO2. Forty-one patients (55%) developed an acute hyperemia with an average duration of 3 days, while 34 patients (45%) consistently had subnormal flows. Although more prevalent in younger patients, hyperemia was found at all age levels (15 to 85 years). There was a highly significant association between hyperemia and the occurrence of intracranial hypertension, defined as an intracranial pressure above 20 mm Hg. Patients with reduced flow showed little or no evidence of global cerebral ischemia, but instead revealed the expected coupling of CBF and metabolism. The CBF responses to hyperventilation were generally preserved, with the hyperemic patients being slightly more reactive. In 10 patients with reduced flow, hyperventilation resulted in wide AVDO2's suggestive of ischemia.
Abstract:Regional Cerebral Blood Flow Estimated by ™Xenon Inhalation • A method is described for estimating the clearance rate and fractional blood flow of the fast (gray matter) compartment of the brain from the first ten minutes of 133 Xe clearance curves, following a one-minute inhalation. Computer-simulated data were used to test the adequacy of the two-compartmental model employed, and to evaluate the stability of the parameters in the presence of random noise. A comparison was made between this approach and the previously reported three-compartmental analysis. Regional cerebral blood flow data were obtained on 48 young control subjects and 20 elderly demented patients. Hemispheral, regional, and test-retest variations were determined, as well as differences between the groups.
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