Upper Gastrointestinal Bleeding
Blood loss from a lesion proximal to the ligament of Treitz is a time-critical circulatory emergency before it is a diagnostic puzzle, so resuscitation and risk-stratification always precede finding the source.
First principles
Upper GI bleeding is defined by anatomy, and anatomy predicts the two commonest causes
'Upper' GI bleeding means the source lies proximal to the ligament of Treitz: oesophagus, stomach or duodenum. Two very different mechanisms dominate: peptic ulcers, where acid-driven erosion breaches a vessel wall (classically the gastroduodenal or left gastric artery), and oesophageal varices, where portal hypertension from cirrhosis forces blood through thin-walled portosystemic collateral veins that rupture under pressure. Because the underlying mechanisms and mortality differ enormously, the first branch point in every case is: is there a background of chronic liver disease that makes varices likely?
Educational content pending clinical review. Not medical advice.