Correlation of Cerebral and Subcutaneous Glycerol in Severe Traumatic Brain Injury and Association with Tissue Damage.

BACKGROUND: This study is a substudy of a prospective consecutive double-blinded randomized study on the effect of prostacyclin in severe traumatic brain injury (sTBI). The aims of the present study were to investigate whether there was a correlation between brain and subcutaneous glycerol levels and whether the ratio of interstitial glycerol in the brain and subcutaneous tissue (glycerolbrain/sc) was associated with tissue damage in the brain, measured by using the Rotterdam score, S-100B, neuron-specific enolase (NSE), the Injury Severity Score (ISS), the Acute Physiology and Chronic Health Evaluation Score (APACHE II), and trauma type. A potential association with clinical outcome was explored. METHODS: Patients with sTBI aged 15-70 years presenting with a Glasgow Coma Scale Score ≤ 8 were included. Brain and subcutaneous adipose tissue glycerol levels were measured through microdialysis in 48 patients, of whom 42 had complete data for analysis. Brain tissue damage was also evaluated by using the Rotterdam classification of brain computed tomography scans and the biochemical biomarkers S-100B and NSE. RESULTS: In 60% of the patients, a positive relationship in glycerolbrain/sc was observed. Patients with a positive correlation of glycerolbrain/sc had slightly higher brain glycerol levels compared with the group with a negative correlation. There was no significant association between the computed tomography Rotterdam score and glycerolbrain/sc. S-100B and NSE were associated with the profile of glycerolbrain/sc. Our results cannot be explained by the general severity of the trauma as measured by using the Injury Severity Score or Acute Physiology and Chronic Health Evaluation Score. CONCLUSIONS: We have shown that peripheral glycerol may flux into the brain. This effect is associated with worse brain tissue damage. This flux complicates the interpretation of brain interstitial glycerol levels. We remind the clinicians that a damaged blood-brain barrier, as seen in sTBI, may alter the concentrations of various substances, including glycerol in the brain. Awareness of this is important in the interpretation of the data bedside as well in research.

Prostacyclin Affects the Relation Between Brain Interstitial Glycerol and Cerebrovascular Pressure Reactivity in Severe Traumatic Brain Injury.

BACKGROUND: Cerebral injury may alter the autoregulation of cerebral blood flow. One index for describing cerebrovascular state is the pressure reactivity (PR). Little is known of whether PR is associated with measures of brain metabolism and indicators of ischemia and cell damage. The aim of this investigation was to explore whether increased interstitial levels of glycerol, a marker of cell membrane damage, are associated with PR, and if prostacyclin, a membrane stabilizer and regulator of the microcirculation, may affect this association in a beneficial way. MATERIALS AND METHODS: Patients suffering severe traumatic brain injury (sTBI) were treated according to an intracranial pressure (ICP)-targeted therapy based on the Lund concept and randomized to an add-on treatment with prostacyclin or placebo. Inclusion criteria were verified blunt head trauma, Glasgow Coma Score ≤ 8, age 15-70 years, and a first measured cerebral perfusion pressure of ≥ 10 mmHg. Multimodal monitoring was applied. A brain microdialysis catheter was placed on the worst affected side, close to the penumbra zone. Mean (glycerolmean) and maximal glycerol (glycerolmax) during the 96-h sampling period were calculated. The mean PR was calculated as the ICP/mean arterial pressure (MAP) regression coefficient based on hourly mean ICP and MAP during the first 96 h. RESULTS: Of the 48 included patients, 45 had valid glycerol and PR measurements available. PR was higher in the placebo group as compared to the prostacyclin group (p = 0.0164). There was a positive correlation between PR and the glycerolmean (ρ = 0.503, p = 0.01) and glycerolmax (ρ = 0.490, p = 0.015) levels in the placebo group only. CONCLUSIONS: PR is correlated to the glycerol level in patients suffering from sTBI, a relationship that is not seen in the group treated with prostacyclin. Glycerol has been associated with membrane degradation and may support glycerol as a biomarker for vascular endothelial breakdown. Such a breakdown may impair the regulation of cerebrovascular PR.