Optimal Cerebral Perfusion Pressure in Brain Injury: Physiological Relationships and Outcome.

Background and objectives: The priority for measuring and optimizing physiological metrics in brain injury care remains to be determined. Calculating and targeting optimal cerebral perfusion pressure (CPPopt) is an emerging treatment paradigm, but its association with other parameters and outcome is uncertain. A previous analysis of 22 patients found that brain tissue oxygenation (PbtO2) peaked when CPP values were near CPPopt. This study sought to validate those findings using a distinct, larger cohort. It also studied the relationship between CPPopt and physiological parameters related to intracranial dynamics and with neurological outcome.

Methods: PbtO2, intracranial pressure (ICP), and arterial blood pressure data were collected during a 15-year period from 432 brain injury patients at 4 cooperating trauma centers. CPPopt was retrospectively computed.

Results: The median age was 36 years (n = 316), the median admission Glasgow coma score was 6 (n = 323), and 75% of the patients were men (n = 324). In aggregate data, PbtO2 peaked at CPP values near CPPopt (+/- 2 mm Hg). Proportion of out-of-range ICP measurements (>22 mm Hg) and positive pressure reactivity index were higher in dying and unfavorable outcome groups, and increased with worsening outcome. Time spent near CPPopt was significantly higher in dying patients but not in patients with unfavorable outcome. Time near CPPopt was, however, correlated with improving outcome. Proportion of out-of-range PbtO2 (<20 mm Hg) was not associated with outcome or mortality.

Conclusion: The results verify CPPopt as physiologically significant and that in aggregate data achievement of CPPopt is associated with optimized PbtO2. Compliance with the ICP treatment threshold was, though, the only modifiable physiological variable associated with both functional outcome and mortality. Our results support optimization of ICP with highest priority. Further study is required in patients in whom CPPopt is specifically targeted.