Optimal Cerebral Perfusion Pressure Guided by Brain Oxygen Pressure Measurement

Background: Although increasing cerebral perfusion pressure (CPP) is commonly accepted to improve brain tissue oxygen pressure (PbtO₂), it remains unclear whether recommended CPP targets (i. e., >60 mmHg) would result in adequate brain oxygenation in brain injured patients. The aim of this study was to identify the target of CPP associated with normal brain oxygenation. Methods: Prospectively collected data including patients suffering from acute brain injury and monitored with PbtO₂, in whom daily CPP challenge using vasopressors was performed. Initial CPP target was >60 mmHg; norepinephrine infusion was modified to have an increase in CPP of at least 10 mmHg at two different steps above the baseline values. Whenever possible, the same CPP challenge was performed for the following days, for a maximum of 5 days. CPP "responders" were patients with a relative increase in PbtO₂ from baseline values > 20%. Results: A total of 53 patients were included. On the first day of assessment, CPP was progressively increased from 73 (70-76) to 83 (80-86), and 92 (90-96) mmHg, which resulted into a significant PbtO₂ increase [from 20 (17-23) mmHg to 22 (20-24) mmHg and 24 (22-26) mmHg, respectively; p < 0.001]. Median CPP value corresponding to PbtO₂ values > 20 mmHg was 79 (74-87) mmHg, with 2 (4%) patients who never achieved such target. Similar results of CPP targets were observed the following days. A total of 25 (47%) were PbtO₂ responders during the CPP challenge on day 1, in particular if low PbtO₂ was observed at baseline. Conclusions: PbtO₂ monitoring can be an effective way to individualize CPP values to avoid tissue hypoxia. Low PbtO₂ values at baseline can identify the responders to the CPP challenge.