Cholecystitis results from gallstone impaction in the cystic duct causing bile stasis, gallbladder distension, and inflammation. Persistent obstruction leads to mucosal ischemia, secondary bacterial infection (E. coli, Klebsiella), and risk of empyema, gangrene, or perforation with bile peritonitis. Acalculous cholecystitis occurs in critically ill patients from bile stasis without stones. The nurse must perform comprehensive pain assessment, manage fluid resuscitation, administer antibiotics and analgesics, monitor for surgical complications, and coordinate perioperative care.