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

The priority for measuring and optimizing physiological metrics in brain injury care remains to be determined. Calculating and targeting optimal cerebral perfusion pressure (CPP opt ) is an emerging treatment paradigm, but its association with other parameters is uncertain. A previous analysis of 22 patients found that brain tissue oxygenation (P bt O 2 ) peaked when CPP values were near CPP opt . This study sought to validate those findings using a distinct, larger cohort. It also studied the relationship between CPP opt and physiological parameters related to intracranial dynamics and with neurological outcome.

P bt O 2 , 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. CPP opt was retrospectively computed.

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, P bt O 2 peaked at CPP values near CPP opt (+/- 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 CPP opt was significantly lower in dying patients but not in patients with unfavorable outcome. Time near CPP opt was, however, correlated with better outcome. Proportion of out-of-range P bt O 2 (<20 mm Hg) was not associated with outcome or mortality.

The results verify CPP opt as physiologically significant and that in aggregate data achievement of CPP opt is associated with maximized P bt O 2 . 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 CPP opt is specifically targeted.