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Does Targeting CPP at CPPopt Actually Improve Cerebrovascular Reactivity? A Secondary Analysis of the COGiTATE
Erta Beqiri1, Jeanette Tas2,3,4, Marek Czosnyka5
1Brain Physics Laboratory, Department of Clinical Neurosciences, Division of Neurosurgery, University of Cambridge, Cambridge, UK. vb391@cam.ac.uk.
Background:
The 'CPPopt-Guided Therapy: Assessment of Target Effectiveness' (COGiTATE) randomised controlled trial demonstrated the feasibility and safety of targeting an automated cerebral perfusion pressure (CPP) tailored to optimize cerebrovascular autoregulation (CPPopt) in patients with traumatic brain injury (TBI) requiring intracranial pressure management. The average values of the autoregulation index known as the pressure reactivity index (PRx) were not different between the intervention (CPP target = CPPopt) and control (CPP target = 60-70 mmHg) groups of the trial. This secondary analysis was performed to investigate whether: (1) in the intervention group, PRx was closer to PRxopt (PRx at CPPopt) values, indicating a more preserved reactivity, as opposed to in the control group; (2) in the intervention group, patients experienced lower hourly PRx when CPP was close to the CPPopt-based target.
Methods:
We analyzed data from the 28 and 32 patients randomized to the control and intervention groups of the COGiTATE study, respectively. We compared hourly averaged ΔPRx (PRx minus PRxopt, where PRxopt is PRx at CPPopt) between the two groups, focusing on periods of globally preserved/homogeneous autoregulation (negative PRxopt). For each patient in the intervention group, PRx values in periods when ΔCPP (CPP minus CPPopt target) was between -5 and + 5 mm Hg were compared to values in periods when ΔCPP was outside this range.
Results:
The median ΔPRx was significantly lower in the intervention group for negative PRxopt (Mann-Whitney U-test, p < 0.001). For each patient in this group, the median PRx was lower in periods when CPP was close to the CPPopt-based target (Wilcoxon test, p < 0.001).
Conclusions:
Despite no statistically significant difference in the grand mean PRx, our results suggest that targeting CPPopt does provide a way of improving cerebrovascular reactivity in patients with TBI, offering a rational intervention for trials that address this issue. We also bring insight into aspects of the PRx/CPP relationship that should be considered for autoregulation-guided management for future clinical protocols and trials design.
