**3. Conclusions**

Aortic arch operation is one of the most complex surgeries in the current era. The introduction of hypothermic circulatory arrest has provided a great safety in protection of organs, especially for brain. Neurophysiological monitoring using intraoperative EEG plays a critical role in this field to help surgeons direct circulatory management and give clues about conditions of brain ischemia. With the traditional deep hypothermic circulatory arrest approach, electrocerebral inactivity is usually achieved, and surgeons are ensured that circulatory arrest can be achieved safely. However, with the advent of adjunctive cerebral perfusion techniques, there is a certain trend that hypothermic circulatory arrest is achieved at higher degrees (moderate hypothermic circulatory arrest) than deep hypothermia where electrocerebral inactivity is not achieved, and the surgical outcomes with moderate hypothermia have been favorable. Moderate hypothermic technique can avoid the issues associated with deep hypothermia, such as coagulopathy, prolonged cardiopulmonary bypass, and direct neuronal injury. The electrophysiological findings in moderate hypothermic circulatory arrest have not been established and need to be studied further. It is highly likely that neurological monitoring using EEG in the aortic arch operations will continue to be viewed as a crucial modality to ensure optimal patient safety and as the field continues to develop with new circulatory management strategies and operative techniques.
