The goal of this clinical trial is to investigate the effect of gastrointestinal stimulation with a pacemaker on the length of postoperative bowel paralysis in patients undergoing major abdominal surgery due to metastasizing colorectal cancer, appendiceal cancer or pseudomyxoma peritonei. The main question it aims to answer is if the length of postoperative ileus is reduced when the gastrointestinal tract is stimulated with a pacemaker. All participants will undergo cytoreductive surgery +/- heated intraperitoneal chemotherapy (the standard treatment for colorectal cancer, appendiceal cancer with peritoneal carcinomatosis or pseudomyxoma peritonei). After surgery, but before the abdomen is closed a pace lead will be attached to the stomach, exteriorized trough the abdominal wall and connected to an external pacemaker. The pacemaker is either turned on (experimental group) or off (control group). After surgery, patients will be asked to fill out a diary on bowel movements once a day. Once normal bowel function is regained, the pace lead and pacemaker will be removed trough the abdominal wall with a firm pull.