Continuous monitoring of cerebrovascular autoregulation: a validation study
- 1Department of Neurosurgery, Christian-Albrechts-Universität, Weimarer Strasse 8, D-24106 Kiel, Germany
- 2Department of Neurosurgery, University of Sydney, Westmead Hospital, Level 5, Westmead NSW 2145, Australia
- 3Academic Neurosurgery Unit and Wolfson Brain Imaging Centre, University of Cambridge, Addenbrooke's Hospital, Box 167, Level 4, A Block, Cambridge CB2 2QQ, UK
- Correspondence to: Dr Erhard W Lang, Department of Neurosurgery, Level 5, Westmead Hospital, Sydney, NSW 2145, Australia; keeflang{at}optusnet.com.au
- Received 13 August 2001
- Accepted 10 January 2002
- Revised 21 December 2001
Abstract
Background: Continuous monitoring of dynamic cerebral autoregulation, using a moving correlation index of cerebral perfusion pressure and mean middle cerebral artery flow velocity, may be useful in patients with severe traumatic brain injury to guide treatment, and has been shown to be of prognostic value.
Objective: To compare an index of dynamic cerebral autoregulation (Mx) with an index of static cerebral autoregulation (sRoR).
Methods: Mx was validated in a prospective comparative study against sRoR, using 83 testing sessions in 17 patients with traumatic brain injury. sRoR and Mx were calculated simultaneously during pharmacologically induced blood pressure variations.
Results: Mx was significantly correlated with sRoR (R = −0.78, p < 0.05). Nine patients were found to have failure of cerebral autoregulation, with an sRoR value < 50%. If an Mx value of 0.3 was used as the cut off point for failure of cerebral autoregulation, this index had 100% sensitivity and 90% specificity for demonstrating failure of autoregulation compared with the sRoR. An increase in cerebral blood flow velocity correlated significantly with Mx (R = 0.73, p < 0.05) but not with cerebral perfusion pressure (R = 0.41).
Conclusions: Dynamic and static cerebral autoregulation are significantly correlated in traumatic brain injury. Cerebral autoregulation can be monitored continuously, graded, and reliably assessed using a moving correlation analysis of cerebral perfusion pressure and cerebral blood flow velocity (Mx). The Mx index can be used to monitor cerebral blood flow regulation. It is useful in traumatic brain injury because it does not require any external stimulus.
