(SS#V) Natus Resident/ Fellow Award for Neurocritical Care (2023 Award Winner): The Relationship Between Cerebral Perfusion Pressure, Brain Tissue Oxygen, and Cerebrovascular Pressure Reactivity: A Canadian High Resolution-traumatic Brain Injury (CAHR-TBI) Study

Introduction: Brain tissue oxygen tension (PbtO2) and cerebrovascular reactivity monitoring have emerged as potential modalities to individualize care in moderate/severe traumatic brain injury (TBI). The relationship between these modalities has had limited exploration. The aim of this study was to examine the relationship between PbtO2 and cerebral perfusion pressure (CPP) and examine how this relationship is modified by cerebrovascular pressure reactivity.

Methods: A retrospective multi-institution cohort study utilizing prospectively collected high-resolution physiologic data from the CAnadian High Resolution TBI (CAHR-TBI) Research Collaborative database was performed. The cohort included critically ill TBI patients with intracranial pressure (ICP), arterial blood pressure (ABP), and PbtO2 monitoring treated in one of three Canadian adult intensive care units (ICU) at CAHR-TBI affiliated institutions between 2011 and 2021.

Results: A total of 77 patients met the study inclusion criteria with a total of 377,744 minutes of physiologic data available for the analysis. PbtO2 produced a triphasic curve when plotted against CPP. There was a plateau region flanked by regions of relative ischemia (hypoxia) and hyperemia (hyperoxia). The plateau region shortened when cerebrovascular reactivity was disrupted compared to when it was intact. Additionally, the morphology of the plateau region resembled that found in a recent porcine study examining the relationship between cerebral blood flow (CBF) and CPP.

Conclusion : In this exploratory analysis of a multi-institution high-resolution physiology TBI database, PbtO2 seems to have a triphasic relationship with CPP, over the entire cohort. The CPP range over which the plateau exists is modified by the state of cerebrovascular reactivity and the morphology of the plateau region resembles that found in a recent large animal study evaluating the relationship between CBF and CPP. This supports the notions that in critically ill TBI patients admitted to ICU, PbtO2 may reflect CBF.