The major benign causes of GOO are PUD, gastric polyps, ingestion of caustics, pyloric stenosis, congenital duodenal webs, gallstone obstruction (Bouveret syndrome), pancreatic pseudocysts, and bezoars. Ulcers within the pyloric channel and first poion of the duodenum usually are responsible for outlet obstruction. Hypochloremic, hypokalemic metabolic alkalosis is the classic electrolyte and acid-base imbalance of pyloric stenosis. This prolonged vomiting causes progressive loss of fluids rich in hydrochloric acid, which causes the kidneys to retain hydrogen ions in or of potassium Ref Davidson 23rd edition pg 386