Temporal changes in cerebral tissue oxygenation with cerebrovascular pressure reactivity in severe traumatic brain injury

Objective: To investigate the temporal relationship between cerebrovascular pressure reactivity and brain tissue oxygenation in patients with severe head injury. Methods: In 40 patients, brain tissue oxygenation and intracranial pressure were monitored. Time-averaged values for intracranial pressure (ICP), mean arterial pressure (MAP), cerebral perfusion pressure (CPP) and brain tissue oxygenation (PtiO(2)) were computed. The pressure reactivity index (PRx) was calculated. The mean values of the variables were obtained at the 6-h and 72-h post-injury time points, and the difference between the two time points for each of the variables was denoted as delta (delta). Results: Of the 40 patients, 32 were survivors and 8 were non-survivors. Statistically significant differences were present between these two groups with regard to delta MAP (p = 0.013), ICP at 6 h (p = 0.027), CPP at 72 h (p = 0.018), delta CPP (p = 0.033), PRx at 6 h (p = 0.029), PRx at 72 h (p = 0.002), PtiO(2) at 72 h (p < 0.0005) and delta PtiO(2) (p = 0.023) values, reflecting an improvement with time in survivors and a deterioration with time in non-survivors. In non-survivors, the magnitude of change in PtiO(2) and CPP with time correlated in a negative linear fashion (p = 0.042 and 0.029, respectively) with the change in PRx with time, whereas no such relationship was seen in survivors. Conclusion: The severity of brain tissue oxygenation derangement correlates with increasing cerebrovascular dysautoregulation in patients succumbing to severe head injury, supporting the utility of PRx as a monitoring variable and the rationale for a target-driven approach to head injury management.