Flow Replacement Bypass for Aneurysms: Decision-Making Using Intraoperative Blood Flow Measurement

Purpose: There is much debate regarding the optimal strategy for extracranial-intracranial (EC-IC) bypass for complex aneurysms. We introduce the concept of a flow replacement bypass which aims to compensate for loss of flow in the efferent vessels of the aneurysm. The strategy to achieve this utilizes direct intraoperative flow measurements to guide optimal revascularization by matching graft flow to demand. Methods: We reviewed all EC-IC bypass cases performed over a 6 year period. We identified cases in which intraoperative flow measurements using an ultrasonic flow probe were utilized to determine the revascularization strategy, and analyzed the decision-making paradigm. Results: Twenty three cases were analyzed. For terminal aneurysms, flow measurement in the affected vessel at baseline predicted the flow required for full replacement: MCA 50±25cc/min (n=9); PICA 13±7cc/min (n=4); PCA 33cc/min (n=1); SCA 10cc/min (n=1). For proximal ICA aneurysms (n=8), the flow deficit from baseline during carotid temporary occlusion was measured (26±18cc/min, an average of 44% drop from baseline). The adequacy of flow from the superficial temporal artery (STA) or occipital artery (OA), when available, was assessed prior to bypass, and STA, OA or vein interposition grafts were used accordingly. Measurement of bypass flow following anastomosis confirmed not only patency but sufficient flow in all cases: MCA 50±25cc/min, PICA 18±9cc/min, PCA 64cc/min, SCA 12 cc/min, ICA 36±25cc/min (STA) and >200cc/min (vein). Conclusions: Direct intraoperative measurement of flow deficit in aneurysm surgery requiring parent vessel sacrifice can guide the choice of flow replacement graft, and confirm the subsequent adequacy of bypass flow.