Intraoperative measurement of arterial blood flow using a transit time flowmeter: Monitoring of hemodynamic changes during cerebrovascular surgery

Background. The purpose of this study was to examine the utility and reliab ility of arterial flow measurements made with a transit time ultrasonic flo wmeter for monitoring blood flow changes during intracranial and carotid su rgery. Method. A total of 25 patients underwent intra-operative arterial blood flo w measurements. The pulsatile flow curve and mean flow values were obtained using 1- to 6-mm transit time probes with a dual channel flowmeter. Four c ases underwent aneurysm clipping, 11 cases superficial temporal artery (STA ) - middle cerebral artery (MCA) bypass, 2 cases external carotid artery (E CA)- radial artery - MCA bypass for aneurysm trapping, and 8 cases carotid endarterectomy. In aneurysm clipping, blood flow in the branches distal to the aneurysm was measured before and after clipping. Blood flow in the STA was measured before and after STA-MCA anastomosis, and blood flow in the in ternal carotid artery (ICA) cervical portion was measured during carotid en darterectomy. Blood flow in the MCA and STA was monitored during radial art ery grafting. Findings. Blood flow in the STA was elevated after STA-MCA anastomosis. How ever, post-operative hyperperfusion syndrome was found in some cases whose flow elevation was over 50 ml/min. Also in one case of carotid stenosis. of which blood flow of ICA was elevated to 400 ml/min after carotid endartere ctomy, hyperperfusion syndrome was found after surgery. In the cases of MCA aneurysm clipping, decreasing of M2 flow was detected when clipping caused bifurcation stenosis. Interpretation. We found transit time flow measurement useful for managemen t of cerebrovascular surgery: the technique was simple to use and provided stable, reliable results. The method was able to reveal distal branch flow diminution in aneurysm clipping, or residual flow during temporary clipping in aneurysm surgery, and has the potential to predict post-operative compl ications such as hyperperfusion by signalling over-elevation of donor arter y flow in bypass surgery or ICA flow in carotid surgery.