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
ICA, internal carotid artery
MAP, mean arterial pressure
TAV, time-averaged flow velocity
WSS, wall shear stress