Time course of recovery from cerebral vulnerability after severe traumatic brain injury: A microdialysis study

Background: The aim of this study was to evaluate the time course of recovery from cerebral vulnerability, using microdialysis (MD) technique and cerebral vascular autoregulation measurement, to clarify the appropriate timing of subsequent major surgical procedures, and to minimize the possibility of secondary brain injury in patients with severe traumatic brain injury (STBI). Methods: In 3,470 MD samples of 25 patients with STBI, cerebral extracellular biomarkers (glucose, lactate, pyruvate, glycerol, and glutamate) were measured. In addition, to estimate cerebral vascular autoregulaton, the pressure reactivity index (PRx) was calculated with intracranial pressure (ICP) and mean arterial pressure. The data with ICP, cerebral perfusion pressure (CPP), and PRx were collected hourly for 7 days after injury and they were compared with MD biomarkers daily. Results: During the study period, the average ICP and CPP remained stable and were within the threshold of STBI treatment guidelines. After injury, the extracellular glucose concentration decreased, and the levels of glycerol, glutamate, and lactate/pyruvate ratio (LPR), which indicate cerebral ischemia and neural cell damage, increased. On the fourth day after injury, the extracellular glucose concentration improved, and the value of LPR decreased. The average PRx decreased daily and became negative on the fifth day after injury. Conclusion: Our results indicated that cerebral vascular autoregulation would recover on the fourth day after STBI, and cerebral perfusion might be increased by recovery of autoregulation. Thus, subsequent nonemergent surgery should be performed at least 4 days after STBI to prevent secondary brain injury. In addition, we should keep in mind that the cerebral vulnerability might persist for 4 days after suffering STBI.