Measurement protocol
vascular stiffness, Tetanic
To measure the MECAfter sympathetic excitation caused by intubation-related stimulation subsided and the expiratory concentration of sevoflurane stabilized, continuous measurement of vascular stiffness (K value, explained in the next section) was initiated. Electrocardiogram, arterial blood pressure, and PPG data were output to a personal computer from a bedside patient monitor (BSS-9800; Nihon Kohden, Tokyo, Japan). These data were used to calculate the K values in real time. Tetanic stimuli were delivered at 50 Hz for five seconds through a two-pole body surface electrode on the ulnar side of the right hand using an Innervator 252 (Fisher & Paykel Healthcare, Auckland, New Zealand). The initial stimulation intensity was 10 mA and the intensity was increased in 10 mA increments to a maximum of 80 mA. A sufficient interval was provided between each stimulation. After confirming that the K value had returned to the pre-stimulus state, subsequent stimulation was performed. The same expiratory concentration of sevoflurane (0.7 MAC) and predicted effect-site concentration of remifentanil (2 ng/mL) were maintained until skin incision. The ROC