Effects of drinking water combined with acupuncture 2h before anesthesia on gastric volume and postoperative gastrointestinal recovery in patients with colorectal cancer

Interventions: A2 group:Drink 250ml water 2h before anesthesia;B1 group:Preoperative routine diet prohibition + electroacupuncture acupoint stimulation;B2 group:drink 250ml water 2h before anesthesia+electroacupuncture acupoint stimulation;A1 group (control group):Preoperative routine diet prohibition
Primary outcome(s): Gastric volume;First flatus;First defecation;First oral feeding;Cross-sectional area of gastric
Study Design: Parallel