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Anesth Analg 2008; 106:234-239
© 2008 International Anesthesia Research Society
doi: 10.1213/01.ane.0000295802.89962.13
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NEUROSURGICAL ANESTHESIOLOGY

An Assessment of Dynamic Autoregulation from Spontaneous Fluctuations of Cerebral Blood Flow Velocity: A Comparison of Two Models, Index of Autoregulation and Mean Flow Index

Marek Czosnyka, PhD*, Piotr Smielewski, PhD*, Andrea Lavinio, MD*, John D. Pickard, FMedSci*, and Ronney Panerai, PhD{dagger}

From the *Academic Neurosurgical Unit, Addenbrooke’s Hospital, Cambridge, UK; and {dagger}Department of Cardiovascular Sciences, University of Leicester, Leicester, UK.

Address correspondence and reprint requests to Marek Czosnyka, PhD, Academic Neurosurery, Box 167 Addenbrooke’s Hospital, Cambridge CB2 2QQ, UK. Address e-mail to mc141{at}medschl.cam.ac.uk.

Abstract

BACKGROUND: Various methods of assessment of cerebral autoregulation, using spontaneous slow fluctuations of blood flow velocity (FV), arterial blood pressure, and cerebral perfusion pressure, have been used in clinical practice. We studied the association between the dynamic index of autoregulation (ARI) and time correlation index (mean flow index, Mx) in a group of patients after head injury.

METHODS: Fifty head-injured patients of an average age of 31 yr, sedated, paralyzed, and ventilated (mild hypocapnia) with continuous monitoring of arterial blood pressure and intracranial pressure were studied. Cerebral blood FV was monitored daily for 3 days after injury during periods that were free from interventions (e.g., suctioning).

Digitally recorded data were analyzed retrospectively. ARI was calculated as a coefficient graded from 0 (absence of autoregulation) to 9 (strongest autoregulation), describing a dynamic model of autoregulation. Mx was calculated as the correlation coefficient between 40 consecutive 6-s averages of FV and cerebral perfusion pressure and then averaged over the whole recording period. ARI and Mx values, assessed during the first 3 days after injury, were averaged for each patient.

RESULTS: ARI and Mx showed moderately strong mutual linear relationship with correlation r = –0.62; P = 0.0001. Both indices correlated with outcome, indicating worse autoregulation in patients achieving unfavorable outcome.

CONCLUSION: ARI and Mx agree relatively well in head-injured patients. Autoregulation affects outcome after head injury.






Lippincott, Williams & Wilkins Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999 HighWire Press
Copyright © 2008 by the International Anesthesia Research Society.