Intracranial and extracranial vascular bypass (EC-IC bypass) has been widely used in the surgical treatment of smog. Numerous studies have shown that EC-IC bypass significantly reduces the risk of transient ischemic attacks and strokes compared with drug therapy alone. However, transient neurological deficits (TNEs), such as aphasia and hemiparesis, may occur after EC-IC bypass. TNEs are generally considered to be caused by post-bypass hyperperfusion based on imaging data of immediate intraoperative cerebral blood flow and postoperative cerebral blood perfusion. Nitin Mukerji et al. at Stanford University Medical Center, USA, looked closely at the results of real-time cerebral blood flow monitoring in seven patients with smoldering disease who developed TNEs in the left hemisphere after bilateral bypass surgery and suggested that the possible cause of TNEs was localized, transient hypoperfusion due to hyperperfusion and large fluctuations in blood perfusion in the early postoperative period. The findings were published in the October 2014 issue of J Neurosurg. Thirty-one patients with smoker’s disease who underwent superficial temporal artery-middle cerebral artery (STA-MCA) bypass were included in the study: seven men and 24 women; ages 25 to 46 years, mean 32 years. 20 had bilateral hemispheric procedures and 11 had unilateral hemispheric procedures, for a total of 51 lateral hemispheric bypass procedures. A Q500 heat transfer probe (Hemedex) was placed in the frontal lobe adjacent to the anastomosis and connected to a Bowman cerebral blood flow monitor to monitor cerebral blood flow (CBF) after the anastomosis.? The patients were divided into 3 groups: 7 patients operated on the left hemisphere with TNEs as group 1, 19 patients operated on the left hemisphere without TNEs as group 2 and 25 patients operated on the right hemisphere without TNEs as group 3. Real-time CBF was recorded at a period of 8 hours for 50 hours after surgery to compare the differences between the three groups, where groups 2 and 3 were used as controls. The results of cerebral blood flow monitoring revealed that postoperative CBF was extremely unstable and fluctuated widely. group 1 showed a significant increase in initial postoperative perfusion, but a sharp decrease in perfusion in the event of TNEs. the mean perfusion per 8 hours in group 1 was significantly different from the other two groups, suggesting that postoperative perfusion changes were greater in group 1, i.e., patients with left hemisphere surgery with TNEs, than in groups 2 and 3. Thus, the authors suggest that the development of TNEs after bypass surgery in patients with smog may be due to a combination of competition between fresh blood flow from the STA and collateral blood flow and cerebrovascular autoregulatory dysfunction leading to a decrease in local CBF. Therefore, it is recommended that blood pressure lowering should not be emphasized when TNEs occur after bypass surgery for smog disease, but rather blood pressure should be adjusted rationally by monitoring CBF with real-time data.