Blood flow monitoring systems such as photoplethysmogram (PPG) and laser Doppler flowmetry (LDF) are useful for intraoperative determination of a successful endoscopic thoracic sympathectomy (ETS) procedure, as they are able to indicate a sympatholytic response. A recently developed novel arterial mechanical impedance monitor has been shown able to provide a value for peripheral arterial stiffness, shown as K. In this retrospective cohort study, we compared the intensity of K with that of PPG and LDF during ETS procedures. Seventy-nine patients with hyperhidrosis underwent a surgical sympathectomy procedure under general anesthesia, during which they were managed by monitors attached to the tips of their fingers. Circulatory variables before and after the surgical procedure were recorded during ETS, then the ratios of those indices were statistically compared. With a statistical significance level of p < 0.05, K was shown to have a greater alteration as compared to PPG and LDF at the time of skin incision as well as neural clipping in both hands. We concluded that arterial mechanical impedance shown by K is a more sensitive monitor of sympathetic activity derived from vasoconstriction and vasodilation during an ETS procedure as compared to PPG and LDF.