Metabolic Crisis without Brain Ischemia is Common after Traumatic Brain Injury: A Combined Microdialysis and Positron Emission Tomography Study

Abstract

Brain trauma is accompanied by regional alterations of brain metabolism, reduction in metabolic rates and possible energy crisis. We hypothesize that microdialysis markers of energy crisis are present during the critical period of intensive care despite the absence of brain ischemia. In all, 19 brain injury patients (mean GCS 6) underwent combined positron emission tomography (PET) for metabolism of glucose (CMRglu) and oxygen (CMRO 2 ) and cerebral microdialysis (MD) at a mean time of 36 h after injury. Microdialysis values were compared with the regional mean PET values adjacent to the probe. Longitudinal MD data revealed a 25% incidence rate of metabolic crisis (elevated lactate/pyruvate ratio (LPR)440) but only a 2.4% incidence rate of ischemia. Positron emission tomography imaging revealed a 1% incidence of ischemia across all voxels as measured by oxygen extraction fraction (OEF) and cerebral venous oxygen content (CvO 2 ). In the region of the MD probe, PET imaging revealed ischemia in a single patient despite increased LPR in other patients. Lactate/pyruvate ratio correlated negatively with CMRO 2 (Po0.001), but not with OEF or CvO 2 . Traumatic brain injury leads to a state of persistent metabolic crisis as reflected by abnormal cerebral microdialysis LPR that is not related to ischemia.

Alterations in Cerebral Oxygen Metabolism after Traumatic Brain Injury in Children

“…13,25 The subacute phase (3 months after injury) is less well studied, but low CBF has been reported. 7,28 This time course is remarkably consistent with the crosssectional view provided by our data. In our cohort, CBF was measured using arterial spin labeling.…”

Early Nonischemic Oxidative Metabolic Dysfunction Leads to Chronic Brain Atrophy in Traumatic Brain Injury

“…Indeed, in a preliminary study, we used a combination of early PET imaging and longitudinal cerebral microdialysis monitoring to study metabolic disturbance in the acute period after trauma. In that study, we reported that the burden of microdialysis lactatepyruvate ratio correlated negatively with CMRO 2 (Vespa et al, 2005). Factors responsible for global or regional brain atrophy have not been explored The correlation between atrophy and elevated ICP lends indirect credence that the patients' brains were in distress.…”

“…In our previous study combining PET and microdialysis in TBI patients, we found a lower mean ischemic brain volume, 1.5 cm 3 , which translates into 1.5% of total brain volume; we also documented persistent and long-lasting evidence of metabolic crisis lasting several days despite the absence of brain ischemia. (Vespa et al, 2005). Positron emission tomography imaging conducted both at early time points and repeatedly over several days would be required to determine the presence of regional ischemia.…”

Cerebral Blood Flow and Autoregulation After Pediatric Traumatic Brain Injury

“…Regional alterations of brain metabolism, reduction in metabolic rates and energy crisis have been demonstrated in adult patients after TBI [71][72][73]. Although the incidence of cerebral ischemia was reported to be low (1% when using oxygen extraction fraction and cerebral venous oxygen content, and 2.4% when using microdialysis technique), the incidence of metabolic crisis (elevated lactate/pyruvate ratio) following TBI was high (25%) [74].…”