Acute Lower GI Bleeds: Pathogenesis and Clinical Findings
Diverticulosis
Formation of diverticula (outpouchings of the bowel wall)
Intestinal vessels are stretched over the domes of the diverticula
Angiodysplasia
Formation of
dilated, thin- walled vessels in GI tract mucosa/ submucosa
Colorectal Cancer
Infectious Colitis
Invasion of bacteria and/or bacterial toxins into intestinal wall
Cell damage and cell death
Sloughing off of intestinal epithelial cells
Ischemic Colitis
↓ Blood flow to a portion of the colon
Lack of oxygen delivery to colon wall
Necrosis (cell death) in the colon wall
Inflammatory Bowel Diseases (Note: these are chronic diseases and rarely present with acute lower GI bleed)
New, extremely friable blood vessels develop within the tumor
Malignant tissue invades the colon wall and disrupts colonic blood vessels
Crohn Disease
Immune- mediated full thickness inflammation of bowel wall
Ulcer formation and disruption of intestinal vessels
Ulcerative Colitis
Recurrent immune- mediated inflammation of colon mucosa
Authors:
Miranda Schmidt Illustrator:
Mizuki Lopez Reviewers:
Vina Fan,
Ben Campbell, Kerri Novak*
* MD at initial time of publication
Acute Lower GI Bleed
↑ Risk for vessel damage and rupture
Blood travels rapidly through GI tract
Hematochezia
(bright red blood per rectum)
May result in significant blood loss
Blood from the small intestine or right colon travels a longer distance through the GI tract
Bacteria in the GI tract has time to oxidize hemoglobin in the blood
Oxidization makes blood a darker color
Melena (rare in a lower GI bleed) (tarry black stool)
Inferior Vena Cava
Diaphragm
Esophagus
Loss of red
blood cells results in a loss of hemoglobin (a component of red blood cells)
Fluid from the extravascular space moves into the blood vessels to maintain vascular volume
Fluid is administered in a healthcare setting to compensate for blood loss
Hypovolemic Shock (rare in a lower GI bleed) (↓ Oxygen delivery to tissues due to low blood volume)
See “Hypovolemic Shock” slide for signs and symptoms
Lower GI Bleeds
are intra-luminal GI tract bleeds that occur anywhere distal to the ligament of Treitz (transition between duodenum and jejunum)
After 24 hours, the addition of fluid to the intravascular space dilutes hemoglobin in the blood
Normocytic Anemia
Duodenum
Ligament of Treitz
Legend:
Pathophysiology
Mechanism
Sign/Symptom/Lab Finding
Complications
Published August 31, 2022 on www.thecalgaryguide.com