Continuous assessment of cerebrovascular autoregulation after traumatic brain injury using brain tissue oxygen pressure reactivity

Objective: To evaluate whether two newly developed indexes of brain tissue oxygen pressure reactivity (ORx and b(ptiO2)) provide information on the status of cerebrovascular autoregulation after traumatic brain injury. This was accomplished by analyzing the relationship between these indexes and an index of cerebrovascular pressure reactivity (PRx). PRx is an established parameter for estimation of cerebrovascular autoregulation. Design: Retrospective analysis of prospectively collected data. Setting: Neurosurgical intensive care unit of a university hospital. Patients: Twenty-seven patients suffering from severe traumatic brain injury. Interventions: Continuous monitoring of mean arterial blood pressure, intracranial pressure, cerebral perfusion pressure, and partial pressure of brain tissue oxygen (p(tiO2)) was performed for an average of 6.5 days. ORx was calculated as a moving correlation coefficient between values of cerebral perfusion pressure and P-tiO2. The b(ptiO2) was calculated as a moving value of the slope of the linear regression function between cerebral perfusion pres- sure and P-tiO2. PRx was calculated as a moving correlation coefficient between values for intracranial pressure and mean arterial blood pressure. Outcome was assessed at 6 months after traumatic brain injury (Glasgow Outcome Scale). Measurements and Main Results: Both ORx and b(PtiO2) correlated significantly with PRx (r =.55 for ORx, r =, 52 for b PV02' p < .01). PRx and ORx showed a significantly negative correlation to the monitored P-tiO2 values (r = -.42 for PRx, r = -.41 for ORx, p < .05) and outcome (r = -.52 for PRx, r = -.62 for ORx, p < .01), whereas b(ptiO2) did not. Conclusions: ORx and, to a lesser extent, b(ptiO2) correlated with the autoregulatory marker PRx and provide additional information about the status of cerebrovascular autoregulation after traumatic brain injury. The data also suggested that patients with impaired autoregulation are at increased risk for secondary cerebral hypoxia.