The investigators assume that transcutaneous electric acupoint stimulation (TEAS) pretreatment may activate the endogenous protective mechanism, as a result protect the patients against subsequent surgical stress pregnancy. And TEAS may induce the production of endogenous analgesic transmitters, so develop an anesthetic-sparing effect. The investigators believe this intervention will reduce the subsequent incidence, duration and severity of organ dysfunction, possibly reducing the morbidity, even mortality. So in this study, the investigators hypothesize that TEAS before anesthesia and during surgery would decrease the morbidity and mortality of postoperative complications in 30 days after digestive surgery in elderly patients .