Zollinger-Ellison syndrome (ZES) is caused by gastrin-secreting neuroendocrine tumors (gastrinomas) that produce massive, unregulated gastrin secretion, driving continuous maximal stimulation of parietal cell hydrogen-potassium ATPase pumps and causing gastric acid hypersecretion. Fasting serum gastrin levels are markedly elevated (often greater than 1000 pg/mL, normal less than 100), and basal acid output exceeds 15 mEq/hour. The excess acid overwhelms duodenal buffering capacity, causing severe peptic ulcer disease (often multiple, atypical locations including distal duodenum and jejunum), esophagitis, and secretory diarrhea (acid inactivates pancreatic lipase causing fat malabsorption, and the volume of acidic gastric secretion exceeds absorptive capacity). Approximately 25% of gastrinomas occur as part of multiple endocrine neoplasia type 1 (MEN1), along with parathyroid hyperplasia and pituitary adenomas. More than 60% of gastrinomas are malignant with potential for hepatic metastases. The nurse administers high-dose proton pump inhibitor therapy as prescribed (doses significantly higher than standard -- often omeprazole 60-120 mg daily), monitors for complications of acid hypersecretion (GI bleeding, perforation, stricture), monitors gastrin levels, assesses nutritional status and malabsorption, coordinates imaging surveillance for tumor localization and metastatic disease, and screens for...