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Mean Arterial Pressure Required for Maintaining Patency of Extracranial-to-Intracranial Bypass Grafts: An Investigation With Computational Hemodynamic ModelsCase Series

Sia, Sheau Fung MS; Qian, Yi PhD; Zhang, Yu PhD; Morgan, Michael Kerin MD

doi: 10.1227/NEU.0b013e318266e6c2
Research-Human-Clinical Studies

BACKGROUND: Maintaining flow in a newly established high-flow bypass into the intracranial circulation may be threatened by low blood pressure.

OBJECTIVE: To identify mean arterial blood pressure below which early graft failure may ensue.

METHODS: Computational fluid dynamic blood flow simulation and Doppler ultrasound–derived velocities were combined to study 12 patients with common carotid–to–intracranial (internal carotid artery in 9 and middle cerebral artery in 3) arterial brain bypass with interposition of the saphenous vein. Patients underwent carotid duplex and high-resolution computed tomography angiography to obtain the necessary data. A mean time-averaged pressure gradient across both anastomoses of the graft was then calculated.

RESULTS: The bypass graft mean blood flow ± SD was 180.3 ± 76.2 mL/min (95% confidence interval: 132-229). The mean time-averaged pressure gradient ± SD across the bypass graft was 10.2 ± 8.7 mm Hg (95% confidence interval: 4.6-15.7). This compared with a mean pressure gradient ± SD on the contralateral carotid of 21.7 ± 13.8 mm Hg. From these data, the minimum mean ± SD systemic pressure necessary to maintain graft flow of at least 40 mL/min was 61.6 ± 2.31 mm Hg, and the mean peak wall shear stress ± SD at the proximal anastomosis was 0.8 ± 0.7 Pa (95% confidence interval: 0.3-1.2).

CONCLUSION: Early postoperative mean arterial pressure less than approximately 60 mm Hg may induce blood flow in the bypass to decrease to less than 40 mL/min, a flow below which low shear stress may lead to early graft occlusion.

ABBREVIATIONS: CCA, common carotid artery

CFD, computational fluid dynamics

CI, confidence interval

ECA, external carotid artery

EC-IC, extracranial-to-intracranial

ICA, internal carotid artery

MAP, mean arterial pressure

TAV, time-averaged flow velocity

WSS, wall shear stress

Australian School of Advanced Medicine, Macquarie University, Sydney, New South Wales, Australia

Correspondence: Michael K. Morgan, MD, Health and Medical Development, Macquarie University, 2 Technology Place, Macquarie University, Sydney, NSW 2109, Australia. E-mail: michael.morgan@mq.edu.au

Received February 2, 2012

Accepted June 12, 2012

Copyright © by the Congress of Neurological Surgeons