Molecular and Cellular Mechanisms of Traumatic Cerebral Vascular Injury

Novel index for predicting mortality during the first 24 hours after traumatic brain injury

OBJECTIVE

Failure of cerebral autoregulation and subsequent hypoperfusion is common during the acute phase of traumatic brain injury (TBI). The cerebrovascular pressure-reactivity index (PRx) indirectly reflects cerebral autoregulation and has been used to derive optimal cerebral perfusion pressure (CPP). This study provides a method for the use of a combination of PRx, CPP, and intracranial pressure (ICP) to better evaluate the extent of cerebral hypoperfusion during the first 24 hours after TBI, allowing for a more accurate prediction of mortality risk.

METHODS

Continuous ICP and arterial blood pressure (ABP) signals acquired from 295 TBI patients during the first 24 hours after admission were retrospectively analyzed. The CPP at the lowest PRx was determined as the optimal CPP (CPPopt). The duration of a severe hypoperfusion event (dHP) was defined as the cumulative time that the PRx was > 0.2 and the CPP was < 70 mm Hg with the addition of intracranial hypertension (ICP > 20 or > 22 mm Hg). The outcome was determined as 6-month mortality.

RESULTS

The cumulative duration of PRx > 0.2 and CPP < 70 mm Hg exhibited a significant association with mortality (p < 0.001). When utilized with basic clinical information available during the first 24 hours after admission (i.e., Glasgow Coma Scale score, age, and mean ICP), a dHP > 25 minutes yielded a significant predictive capacity for mortality (p < 0.05, area under the curve [AUC] = 0.75). The parameter was particularly predictive of mortality for patients with a mean ICP > 20 or > 22 mm Hg (AUC = 0.81 and 0.87, respectively).

CONCLUSIONS

A short duration (25 minutes) of severe hypoperfusion, evaluated as lowered CPP during worsened cerebrovascular reactivity during the 1st day after TBI, is highly indicative of mortality.

Vascular endothelial growth factor is increased in cerebrospinal fluid after traumatic brain injury in infants and children

OBJECTIVE

Vascular endothelial growth factor (VEGF) is an important regulator of angiogenesis, the formation of which is triggered by hypoxia, cytokines, and growth factors and is also induced by activation of the adenosine 2B receptor. VEGF is neuroprotective in several models of experimental brain injury and is increased in brain after traumatic brain injury (TBI) in humans and experimental animals. Adenosine is a neuroprotective purine metabolite that increases in cerebrospinal fluid (CSF) after clinical TBI in children. We hypothesized that VEGF levels would 1). be increased in CSF after TBI in infants and children, and 2). be preceded by increases in CSF adenosine. To test this hypothesis, we designed a case-control study to compare the CSF of infants and children after severe TBI with that of uninjured children.

METHODS

Using an Institutional Review Board-approved protocol, we compared CSF concentrations of VEGF (by enzyme-linked immunosorbent assay) and adenosine (by high-performance liquid chromatography) in 73 samples from 14 infants and children with severe TBI (Glasgow Coma Scale score <or=8) with those in CSF from 5 noninjured control subjects. Patients received standard neurointensive care.

RESULTS

Mean VEGF levels were increased after TBI versus control (39.8 +/- 6.2 versus 14.9 +/- 1.5 ng/dl, mean +/- standard error of the mean, P = 0.0002) and peaked at 91.6 +/- 26.4 ng/dl, approximately 6 times control (P = 0.001). Peak VEGF occurred at 22.4 hours after injury. There was a trend toward increased adenosine concentration after TBI versus control (18.3 +/- 3.5 versus 11.5 +/- 2.3 nmol/L), but this did not reach statistical significance. A multivariate regression model showed an independent, significant association between the concentrations of VEGF and adenosine.

CONCLUSION

VEGF is increased in CSF after pediatric TBI, and this increase is associated with an increase in CSF adenosine. These results may imply that a component of the vascular regenerative response of the brain is initiated rapidly after TBI and continues for several days after injury. Further investigation is warranted to determine 1). whether this association is causative, 2). the role of adenosine in triggering the increase in CSF VEGF concentration, and 3). the exact role VEGF that plays after injury.