Gastric bypass surgery Los Angeles methods are performed under a general anesthesia. A Los Angeles gastric bypass surgery requires 2 to 3 days of hospital stay. During a gastric bypass Los Angeles procedure, the patient's digestive system will be altered by re-routing the intestines. Before the gastric bypass surgery Los Angeles doctors re-route the intestines, they first divide the stomach into pouches with volume of 15 to 20 cc.