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The Relationship Between Cerebral Blood Flow Autoregulation and Cerebrovascular Pressure Reactivity After Traumatic Brain Injury

Budohoski, Karol P. MD*; Czosnyka, Marek PhD*; de Riva, Nicolas MD*,‡; Smielewski, Peter PhD*; Pickard, John D. FMedSci*,§; Menon, David K. PhD§,¶; Kirkpatrick, Peter J. FMedSci*; Lavinio, Andrea MD

doi: 10.1227/NEU.0b013e318260feb1
Research-Human-Clinical Studies

BACKGROUND: Cerebrovascular pressure reactivity is the principal mechanism of cerebral autoregulation. Assessment of cerebral autoregulation can be performed by using the mean flow index (Mx) based on transcranial Doppler ultrasonography. Cerebrovascular pressure reactivity can be monitored by using the pressure reactivity index (PRx), which is based on intracranial pressure monitoring. From a practical point of view, PRx can be monitored continuously, whereas Mx can only be monitored in short periods when transcranial Doppler probes can be applied.

OBJECTIVE: To assess to what degree impairment in pressure reactivity (PRx) is associated with impairment in cerebral autoregulation (Mx).

METHODS: A database of 345 patients with traumatic brain injury was screened for data availability including simultaneous Mx and PRx monitoring. Absolute differences, temporal changes, and association with outcome of the 2 indices were analyzed.

RESULTS: A total of 486 recording sessions obtained from 201 patients were available for analysis. Overall a moderate correlation between Mx and PRx was found (r = 0.58; P < .001). The area under the receiver operator characteristic curve designed to detect the ability of PRx to predict impaired cerebral autoregulation was 0.700 (95% confidence interval: 0.607-0.880). Discrepancies between Mx and PRx were most pronounced at an intracranial pressure of 30 mm Hg and they were significantly larger for patients who died (P = .026). Both Mx and PRx were significantly lower at day 1 postadmission in patients who survived than in those who died (P < .01).

CONCLUSION: There is moderate agreement between Mx and PRx. Discrepancies between Mx and PRx are particularly significant in patients with sustained intracranial hypertension. However, for clinical purposes, there is only limited interchangeability between indices.

ABBREVIATIONS: ABP, arterial blood pressure

BF, cerebral blood flow

CBV, cerebral blood volume

CPP, cerebral perfusion pressure

FV, flow velocity

GCS, Glasgow Coma Scale

GOS, Glasgow Outcome Scale

ICP, intracranial pressure

Mx, mean flow index

PRx, pressure reactivity index

ROC, receiver operator characteristic

TBI, traumatic brain injury

TCD, transcranial Doppler

*Division of Neurosurgery, Department of Clinical Neurosciences, Addenbrooke's Hospital, University of Cambridge, Cambridge, United Kingdom

Department of Anaesthesiology, Hospital Clinic de Barcelona, Universitat de Barcelona, Barcelona, Spain

§Wolfson Brain Imaging Centre, Department of Clinical Neurosciences, Addenbrooke's Hospital, University of Cambridge, Cambridge, United Kingdom

University Department of Anaesthesia, Addenbrooke's Hospital, University of Cambridge, Cambridge, United Kingdom

Department of Anaesthesia, Cambridge University Hospitals NHS Foundation Trust, Addenbrooke's Hospital, Cambridge, United Kingdom

Correspondence: Karol P. Budohoski, MD, Department of Neurosurgery, Medical Center for Postrgraduate Training, Mazovia Brodnowski Hospital, Ul. Kondratowicza 8, 03-242 Warsaw, Poland

Received December 15, 2011

Accepted May 9, 2012

Copyright © by the Congress of Neurological Surgeons