Effect of Transcutaneous Electrical Nerve Stimulation Based on Wrist-ankle Acupuncture Theory on EC50 of Remifentanil Inhibiting Responses to Tracheal Intubation Under General Anesthesia

Before anesthesia induction, two paired of electrode pads will be placed on the upper area 1 and 2 with the skin of the treatment area exposed, and the upper and lower juxtaposition method will be adopted. The electrodes were placed close to the skin and connected with TENStem eco basic (Wuxi Jiajian Medical Device Co., Ltd.). Upper area 2 is at the middle of the palmar side of the forearm, between the palmaris longus and flexor carpi radialis.Upper area 1 is between the ulnar border on the little finger side and the flexor carpi ulnaris tendon.Stimulation parameters of TENS-WAA are alternating dense-disperse wave with a frequency of 2Hz and a pulse width of 200μs, and a frequency of 100Hz with a pulse width of 150μs, alternating every 3 seconds ，intensity required to reachthe maximum tolerable level without causing pain, continuous stimulation until the end of surgery.

Before anesthesia induction, two paired of electrode pads will be placed on the same position without current stimulation.