Optimal Cerebral Perfusion Pressure Based on Intracranial Pressure-Derived Indices of Cerebrovascular Reactivity: Which One Is Better for Outcome Prediction in Moderate/Severe Traumatic Brain Injury?

The pressure reactivity index as a measure of cerebral autoregulation and its application in traumatic brain injury management

Severe traumatic brain injury (TBI) is a major cause of morbidity and mortality globally. The Brain Trauma Foundation guidelines advocate for the maintenance of a cerebral perfusion pressure (CPP) between 60 and 70 mmHg following severe TBI. However, such a uniform goal does not account for changes in cerebral autoregulation (CA). CA refers to the complex homeostatic mechanisms by which cerebral blood flow is maintained, despite variations in mean arterial pressure and intracranial pressure. Disruption to CA has become increasingly recognised as a key mediator of secondary brain injury following severe TBI. The pressure reactivity index is calculated as the degree of statistical correlation between the slow wave components of mean arterial pressure and intracranial pressure signals and is a validated dynamic marker of CA status following brain injury. The widespread acceptance of pressure reactivity index has precipitated the consideration of individualised CPP targets or an optimal cerebral perfusion pressure (CPPopt). CPPopt represents an alternative target for cerebral haemodynamic optimisation following severe TBI, and early observational data suggest improved neurological outcomes in patients whose CPP is more proximate to CPPopt. The recent publication of a prospective randomised feasibility study of CPPopt guided therapy in TBI, suggests clinicians caring for such patients should be increasingly familiar with these concepts. In this paper, we present a narrative review of the key landmarks in the development of CPPopt and offer a summary of the evidence for CPPopt-based therapy in comparison to current standards of care.

Intracranial pressure management: moving beyond guidelines

PURPOSE OF REVIEW

The aim of this study was to provide an overview on advances in intracranial pressure (ICP) protocols for care, moving from traditional to more recent concepts.

RECENT FINDINGS

Deep understanding of mechanics and dynamics of fluids and solids have been introduced for intracranial physiology. The amplitude or the harmonics of the cerebral-spinal fluid and the cerebral blood waves shows more information about ICP than just a numeric threshold. When the ICP overcome the compensatory mechanisms that maintain the compliance within the skull, an intracranial compartment syndrome (ICCS) is defined. Autoregulation monitoring emerge as critical tool to recognize CPP management. Measurement of brain tissue oxygen will be a critical intervention for diagnosing an ICCS. Surgical procedures focused on increasing the physiological compliance and increasing the volume of the compartments of the skull.

SUMMARY

ICP management is a complex task, moving far than numeric thresholds for activation of interventions. The interactions of intracranial elements requires new interpretations moving beyond classical theories. Most of the traditional clinical studies supporting ICP management are not generating high class evidence. Recommendations for ICP management requires better designed clinical studies using new concepts to generate interventions according to the new era of personalized medicine.