Introduction:
The optimal cerebral perfusion pressure (CPP) following hypoxic-ischemic brain injury (HIBI) is currently unknown. We retrospectively analyzed intracranial monitoring data from a cohort of patients with HIBI to identify a threshold level for CPP that optimizes cerebrovascular pressure reactivity (a surrogate for CA) while limiting the risk of intracranial hypertension and brain tissue hypoxia.
Hypothesis:
We hypothesized that higher CPP values would be associated with improved cerebrovascular pressure reactivity.
Methods:
ICP, brain tissue oxygen (P
bt
O
2
), MAP, and CPP (defined as MAP - ICP) were recorded continuously and time synchronized for all patients using a bedside monitor (CNS Monitor, Moberg Research). Pressure Reactivity Index (PRx) was calculated as the time varying correlation between MAP and ICP over 5 min intervals updated every minute. The degree of CA impairment (defined as % time PRx > 0.2) was plotted against MAP and CPP, respectively. The relationships between ICP and P
bt
O
2
versus CPP, as well as ICP and P
bt
O
2
versus % time PRx > 0.2, were similarly calculated.
Results:
We analyzed 37 patients (33 cardiac arrest, 4 prolonged hypoxia) with HIBI who underwent intracranial neuromonitoring over a 3 year period. Lower CPP values were associated with higher degrees of CA impairment. The cumulative burden of elevated PRx was significantly lower for CPP values above a cutoff of 85 mmHg compared to lower CPP values (p < 0.001, Wilcoxon rank sum test). A similar cutoff for MAP could not be identified, although lower MAP values were also associated with greater CA impairment. Intracranial hypertension (ICP > 20 mmHg) and brain hypoxia (P
bt
O2 < 20 mmHg) were both associated with CA impairment (p < 0.001 and p < 0.001, respectively, Wilcoxon rank sum test).
Conclusions:
Higher CPP and MAP values appear to be associated with improved CA after HIBI. Given that CA impairment is associated with both intracranial hypertension and brain hypoxia, our work reaffirms the notion that higher blood pressure targets may improve outcome after HIBI. The identification of a distinct CPP cutoff for CA optimization suggests that targeting CPP instead of MAP may be advantageous, although further work is required to clarify this issue.
