An extracranial to intracranial (EC-IC) bypass is used during cerebrovascular surgery:
1) To AUGMENT flow for occlusive cerebrovascular disease (i.e., Moyomoya) or to
2) REPLACE/PRESERVE flow during aneurysm clipping surgery when an aneurysm is trapped and a parent vessel (i.e., internal carotid) must be occluded and sacrificed.
Both strategies depend on direct, quantitative intraoperative flow measurement to help surgeons ascertain that the blood supply from the intended bypass (its carrying capacity) will meet the intracranial demand according to Hagen–Poiseuille equation.
Flow Replacement: At the 8th International Conference on Cerebrovascular Surgery in Taipei, Taiwan in 2006, Dr. Sepideh Amin-Hanjani presented “EC-IC Bypass for Aneurysm: Decision Making Using Intraoperative Flow Measurements.”
Her strategy requires two steps: first, measure and record flow in the artery or territory distal to the aneurysm. Second, temporarily occlude the vessel to be sacrificed and remeasure the distal flow. The difference between the two flows represents the amount of flow deficit that can be expected if the parent vessel is sacrificed. This is the flow that the bypass will have to replace, namely, the flow demand.
The “free” or “Cut Flow” of the intended artery to be used as a bypass is then measured. This Cut Flow value is the flow supply or potential carrying supply of the bypass. It is compared to the deficit flow. If the Cut Flow value equals or exceeds the potential flow deficit, the EC-IC bypass is constructed, and the vessel can be sacrificed with reasonable assurance that the bypass flow (the supply) will compensate for the flow deficit (the demand) from the sacrificed parent vessel. In other words, the supply will satisfy the demand.
Dr. Amin-Hanjani reported that this selective strategy allows the surgeon to:
1) Access the adequacy of a bypass before completing its construction.
2) Select the best vessel match for the bypass.
3) Evaluate the bypass immediately after its construction.
REFERENCES
Amin-Hanjani S, Alaraj A, Charbel FT. “Flow replacement bypass for aneurysms: decision-making using intraoperative blood flow measurements.” Acta Neurochir (Wien) 2010;152(6):1021-32 (Transonic Reference # 7940AH)
Amin-Hanjani S, Du X, Mlinarevich N, Meglio G, Zhao M, Charbel FT. The cut flow index: an intraoperative predictor of the success of extracranial-intracranial bypass for occlusive cerebrovascular disease. Neurosurgery. 2005 Jan;56(1 Suppl):75-85; discussion 75-85.
Stapleton CJ, Atwal GS, Hussein AE, Amin-Hanjani S, Charbel FT. The cut flow index revisited: utility of intraoperative blood flow measurements in extracranial-intracranial bypass surgery for ischemic cerebrovascular disease. J Neurosurg. 2019 Sep 6:1-5.