Mesenteric Ischemia, Ischemia Bowel and Colonic Ischemia for USMLE Step 2

Mesenteric Ischemia, Colon Ischemia, Bowel Ischemia (Acute and Chronic) handwritten lecture, presentation looking at Signs and Symptoms, Anatomy, Physiology, Pathophysiology, Treatment and Management for USMLE Step 2. ANATOMY Superior mesenteric artery comes off the aorta, gives off the middle colic artery which goes to the transverse colon. Then gives off the right colic artery which anostamoses with middle colic artery. On the left side it gives off hte jejunal arteries. Supplies the all the small intestine except the duodenum. The large colon it supplies cecum, ascending colon and proximal transverse colon. Inferior mesenteric artery comes off of the aorta, gives off the left colic artery which will give ascending and descending. Sigmoid arteries goes down to anal canal and hemorrhoids. Covers the distal transverse colon, descending colon, sigmoid colon and the rectum. PATHOPHYSIOLOGY It can be either a arterial occlusion emboli or thrombus, venous occlusion, or arterial vasospasm. If it affects small intestine it is known as mesenteric ischemia including liver, spleen, kidney and large intestine is known as colonic ischemia. Because of high bloodflow and low Oxygen uptake, the bloodflow must be cut in half before there are any symptoms. Therefore during hypotension the bloodflow goes away from the gut and goes towards the brain and heart. Types of injury are due to hypoxia and repurfusion both lead to injury. Gut can compensate 75% for up to 12 hours because takes up more oxygen. Colon is more vulnerable because of hypoperfusion. SIGNS and SYMPTOMS Pain out of proportion to physical findings and of acute onset. Chronic state the bowel is able to compensate with collaterals so there is intestinal angina, pain after eating. Peritoneal findings such as guarding, rigidity, but these are late findings. Distention and decreased bowel sounds which means the ischemia is transmural. Final stage is shock, dehydration. INVESTIGATIONS Laboratory - leukocytosis, hemoconcentration with metabolic acidosis, lactate high specific if rule out shock, DKA, renal/hepatic failur. High amylase 50%, phosphate 80% and D-dimer due to thrombi formation. Imaging modalities are also available. Arterial Embolism Dislodged embolus in LA/LV or valve is more common in the SMA because wider and narrow angle. 3-10 cm from the origin of SMA. Affects the midsegment of the jejunum. In 20% of cases there maybe multiple emboli. Treatment consists of surgical lapratomy with embolectomy and remove artery with emboli. Examine the rest of the bowel for ischemia Thrombolytics if 8 hours and no evidence of peritonitis. If don't improve in 4 hours then go to surgery. Warfain long term. Arterial Thrombus Artherosclerotic plaque occurs if there is history of abdominal trauma or infection. Affects SMA and celiacs at origin. Treatment is revascularization, thrombectomy, resection of non-viable segments. Aspirin for long term control. Venous Thrombus Hypercoagulable state is associated with Virchows triad, such as turbulent flow, endothelial injury, stagnation of blood flow. Affects the ileum, jejunum, colon and duodenum. Vein occludes causing increase resistant and efflux of fluids and edema. Risk Factors consist are DVT, Abdominal mass such as tumor or psuedocyst which occlude the vein physically. Inflammation such as pancreatitis, and diverticulitis which release prothrombogenic cytokines. Myeloproliferative state, Portal Hypertension, Acquire thrombophilis (OCP, Malignancy) Inhertied thrombophilia. Inflammatory bowel disesae. May present acute, subacute or chronic. Non-Occlusive Mesenteric Ischemia .