Review ArticlesCardiac Output and Cerebral Blood Flow: A Systematic Review of Cardio-Cerebral CouplingCastle-Kirszbaum, Mendel MBBS*; Parkin, William Geoffrey MBBS, FANZCA, FCICM†,‡; Goldschlager, Tony FRACS, PhD*,‡; Lewis, Philip M. PhD‡,§ Author Information Departments of *Neurosurgery †Intensive Care, Monash Health Department of ‡Surgery §Electrical and Computer Systems Engineering, Monash University, Melbourne, Vic., Australia The authors have no conflicts of interest to declare. Address correspondence to: Mendel Castle-Kirszbaum, MBBS. E-mail: [email protected]. Journal of Neurosurgical Anesthesiology 34(4):p 352-363, October 2022. | DOI: 10.1097/ANA.0000000000000768 Buy SDC Metrics Abstract Control of cerebral blood flow (CBF) is crucial to the management of neurocritically ill patients. Small studies which have examined the role of cardiac output (CO) as a determinant of CBF have inconsistently demonstrated evidence of cardio-cerebral coupling. Putative physiological mechanisms underpinning such coupling include changes in arterial blood pressure pulsatility, which would produce vasodilation through increased oscillatory wall-shear-stress and baroreceptor mediated reflex sympatholysis, and changes in venous backpressure which may improve cerebral perfusion pressure. We sought to summarize and contextualize the literature on the relationship between CO and CBF and discuss the implications of cardio-cerebral coupling for neurocritical care. A systematic review of the literature yielded 41 studies; all were of low-quality and at high-risk of bias. Results were heterogenous, with evidence for both corroboration and confutation of a relationship between CO and CBF in both normal and abnormal cerebrovascular states. Common limitations of studies were lack of instantaneous CBF measures with reliance on transcranial Doppler–derived blood flow velocity as a surrogate, inability to control for fluctuations in established determinants of CBF (eg, PaCO2), and direct effects on CBF by the interventions used to alter CO. Currently, the literature is insufficiently robust to confirm an independent relationship between CO and CBF. Hypothetically, the presence of cardio-cerebral coupling would have important implications for clinical practice. Manipulation of CBF could occur without the risks associated with extremes of arterial pressure, potentially improving therapy for those with cerebral ischemia of various etiologies. However, current literature is insufficiently robust to confirm an independent relationship between CO and CBF, and further studies with improved methodology are required before therapeutic interventions can be based on cardio-cerebral coupling. Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.