Abstract Details

BOOST-II used a tier-based management protocol based on brain tissue oxygen (PbtO2) and ICP monitoring to reduce BTH after severe TBI. To explore the underlying pathophysiologic mechanisms, we performed a secondary analysis assessing the relationship between BTH and BP. We hypothesized that BP management below lower limit of autoregulation (LLA) leads to cerebral hypoperfusion and BTH, which can be improved with hemodynamic augmentation.

To investigate the effect of cerebral perfusion pressure (CPP) augmentation on cerebral autoregulatory function and brain tissue hypoxia (BTH).

Of the 106 patients enrolled in BOOST-II, 55 patients had simultaneous recordings of arterial BP, ICP, and PbtO2. Autoregulatory function was measured by interrogating changes in PbtO2 in response to fluctuations in CPP using time-correlation analysis. The resulting autoregulatory index (ORx) identified “optimal” CPP (CPPopt) and limits of autoregulation (LA) for each patient. Autoregulatory function and percent time of CPP outside personalized LA were calculated before, during, and after interventions directed at optimizing CPP.

Individualized LA were computed in 50 patients (age 38.2±18.2, 76% male, monitoring time 92.8±42.4 hours). We identified 35 episodes (in 6 patients) of BTH (PbtO2<20 mmHg) treated with CPP augmentation. Following each intervention, mean CPP increased from 73±14 to 79±19 mmHg (p=0.15), and mean PbtO2 improved from 18.4±5.6 to 21.9±5.6 (p=0.01), while autoregulatory function trended towards improvement (ORx: 0.42 vs. 0.37, p=0.14). Though CPPopt and LA remained relatively unchanged, there was a significant decrease in percent time of CPP below LLA in the 60 minutes after compared to before an intervention (11% vs. 23%, p=0.05).

Our analysis suggests that BTH is associated with cerebral hypoperfusion characterized by an increased time of CPP below LLA. Interventions to increase CPP appear to restore autoregulation, resulting in improved PbtO2. Further studies validating the importance of autoregulation as a modifiable variable, with potential to improve outcomes, are needed.