Further understanding of cerebral autoregulation at the bedside: possible implications for future therapy

Abstract

Cerebral autoregulation reflects the ability of the brain to keep the cerebral blood flow (CBF) relatively constant despite changes in cerebral perfusion pressure. It is an intrinsic neuroprotective physiological phenomenon often suggested as part of pathophysiological pathways in brain research. However, despite increasing knowledge of this phenomenon for over 50 years, harnessing cerebral autoregulation as a basis for therapy remains an elegant concept rather than a practical reality. This raises the question is it useful to measure at the bedside or is it merely a scientific curiosity that is too complex and has little pragmatic relevance. In this article, we attempt to answer this question by demonstrating how cerebral autoregulation assessment can have prognostic value, indicate pathological states, and potentially even influence therapy with the use of the ‘optimal cerebral perfusion pressure’ paradigm. Evidence from the literature is combined with bedside clinical examples to address the following fundamental questions about cerebral autoregulation: What is it? How do we measure it? Why is it important? Can we use it as a basis for therapy?

Keywords:

• cerebral autoregulation
• cerebral blood flow
• cerebral perfusion pressure
• critical care medicine
• intracranial pressure
• near-infrared spectroscopy
• stroke
• subarachnoid hemorrhage
• traumatic brain injury
• ultrasound

Acknowledgement

Many thanks to all staff-members of the Neurocritical Care Unit, Academic Neurosurgery Division and Department of Anesthesiology, Addenbrooke's Hospital in Cambridge, UK. Thanks to all present and past members and visiting fellows of Brain Physics Laboratory (Neurosurgery Division, University of Cambridge, UK) who contributed to our understanding of bedside cerebral autoregulation monitoring.

Financial & competing interests disclosure

ICM+ Software is licensed by Cambridge Enterprise, Cambridge, UK, http://www.neurosurg.cam.ac.uk/icmplus/. M Czosnyka has a financial interest in a fraction of the licensing fee and is supported by NIHR Biomedical Research Centre in Cambridge, UK. J Donnelly is supported by a Woolf Fisher scholarship. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

Key issues

• Cerebral autoregulation reflects the ability of the brain to keep its blood flow relatively constant despite changes in the blood pressure perfusing it.

• Cerebral autoregulation can be assessed at the bedside using various invasive and non-invasive techniques.

• Cerebral autoregulation is impaired in many neurologic diseases including traumatic brain injury, subarachnoid hemorrhage, stroke and premature newborns, and the degree of impairment is related to poor outcome.

• Therapies that improve cerebral autoregulation often decrease cerebral blood flow, limiting widespread application.

• Cerebral autoregulation guided ‘optimal arterial blood pressure/cerebral perfusion pressure’ therapy is a promising concept that applies continuous cerebral autoregulation assessment to determine an optimal blood pressure. Optimal arterial blood pressure has the potential to individualize patient management; however, clinical utility has yet to be proven.

• Key areas of future research include the assessment of cerebral autoregulation in various systemic diseases and the investigation of how cerebral autoregulation interacts with other cerebral and systemic physiologic parameters as well as clinical interventions.

Notes