Episode two moves below the ligament of Treitz and then to the mesenteric vessels, carrying the same rule forward: pick the imaging that feeds the next intervention and recognize the pattern that flips the algorithm. Acute lower GI bleeding branches on hemodynamic stability, CT angiography for the unstable patient because it hands interventional radiology the anatomy and colonoscopy at twelve to twenty-four hours for the stable one, with the etiologies read by pattern. Colon ischemia separates from diverticular bleeding on pain before bleeding, and isolated right colon ischemia flips the workup toward mesenteric imaging. Acute mesenteric ischemia turns on recognizing pain out of proportion to exam and reaching for CT angiography before lactate rises, then matching intervention to each of four etiologies. Topics covered Acute lower GI bleeding and the BUN-to-creatinine clue Hemodynamic split: CT angiography versus colonoscopy Diverticular, angiodysplastic, and post-polypectomy bleeding Endoscopic hemostasis and the no-serosa rule Colon ischemia and pain before bleeding Isolated right colon ischemia flipping the algorithm Four etiologies of acute mesenteric ischemia Etiology-specific intervention The lactate trap and initial bundle Key decisions Send the hemodynamically unstable lower GI bleeder to CT angiography first because it images extravasation at about zero point three milliliters per minute and gives IR the anatomy for superselective embolization, and send the stable patient to colonoscopy at twelve to twenty-four hours after rapid polyethylene glycol prep. Suspect a brisk upper source in about fifteen percent of presumed lower GI bleeds and when the BUN-to-creatinine ratio exceeds thirty, and exclude anorectal sources by anoscopy before colonoscopy referral. Treat diverticular and post-polypectomy bleeding with clips or bands rather than deep thermal therapy because the diverticular wall and thinned resection base lack serosa and coagulate to perforation. Distinguish colon ischemia by cramping pain preceding hematochezia within twenty-four hours, treat mild disease supportively, and add antibiotics when the white count exceeds fifteen thousand, BUN exceeds twenty, or ulceration is severe. Image the mesenteric vessels in isolated right colon ischemia because that SMA watershed-equivalent territory can herald silent SMA occlusion, and anchor suspected acute mesenteric ischemia on pain out of proportion with CT angiography now, not lactate first. Match the mesenteric intervention to etiology: embolectomy for SMA embolus, revascularization with bypass or stenting for SMA thrombosis, intra-arterial papaverine with low-flow correction for NOMI, and systemic anticoagulation for mesenteric venous thrombosis, with peritoneal signs sending everyone to laparotomy. For the full chapter with MCQs, tables, and primary-guideline references, visit www.boardpearls.com. Questions or feedback: [email protected].

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“What did the council decide on item 42?” — answered with the speaker and the moment.

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