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.