Pericontusional brain tissue exhibits persistent elevation of lactate/pyruvate ratio independent of cerebral perfusion pressure

OBJECTIVE: To determine whether pericontusional tissue exhibits neurochemical responsiveness to changes in cerebral perfusion pressure as measured by microdialysis lactate/pyruvate ratio. DESIGN: Prospective monitoring with retrospective data analysis. SETTING: Single-center academic neurologic intensive care unit. PATIENTS: Twenty-one patients with severe traumatic brain injury (Glasgow Coma Scale score 3-8). INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Cerebral microdialysis was performed for the initial 7 days after traumatic brain injury. Thirteen patients had microdialysis probes in normal tissue and eight had two probes, one of which was located in pericontusional tissue. Retrospective analysis was performed to determine if microdialysis levels in pericontusional tissue demonstrates higher levels of lactate/pyruvate ratio than normal tissue and if lactate/pyruvate ratio increased with reductions in cerebral perfusion pressure. Univariate analysis revealed higher values for glutamate and lactate/pyruvate ratio in pericontusional tissue compared with normal tissue. However, based on the mixed-effects model analysis, the percent time of elevated lactate/pyruvate ratio was significantly higher in pericontusional tissue (40 ± 59% vs. 17 ± 37%, p < .05), and the mean lactate/pyruvate ratio values showed only a trend relationship (62 ± 134 vs. 34 ± 78, p < .06). When examined by cerebral perfusion pressure threshold, cerebral perfusion pressure <60 mm Hg was not associated with higher lactate/pyruvate ratio values in normal or pericontusional tissue. In addition, no single cerebral perfusion pressure threshold was associated with a significant reduction in lactate/pyruvate ratio in either pericontusional or normal tissue (p < .08). CONCLUSIONS: Sustained increases in lactate/pyruvate ratio occurred more frequently in pericontusional tissue compared with normal brain tissue. The lactate/pyruvate ratio was not related to cerebral perfusion pressure, nor was the percent time-burden of elevated lactate/pyruvate ratio related to any particular sustained cerebral perfusion pressure threshold. Lactate/pyruvate ratio values appear to be elevated despite cerebral perfusion pressure values customarily considered to be adequate.