1.12 Mesenteric Ischemia Flashcards
Describe the three major vascular trunks arise from the aorta to supply the intestines.
o Celiac axis: supplies oxygenated blood to the foregut which includes portions of the liver, spleen, gallbladder, pancreas, esophagus, and stomach.
o Superior mesenteric artery (SMA): delivers blood to the small intestine (distal duodenum extending to the appendix), in addition to the ascending and proximal transverse colon.
o Inferior mesenteric artery (IMA): distributes blood to the distal portion of transverse colon, the descending colon, and the rectum.
Your patient is suffering from mesenteric ischemia. In broad terms, what causes this, how is it categorized?
- Results from decreased blood flow
- Hypoperfusion: shock, vasospasm, or vascular occlusion
- Categorized as either acute or chronic based on how quickly the condition develops
Your patient has acute mesenteric ischemia (AMI). Why is mortality rate 40-70%?
What circumstance leads to 70% fatality?
Describe the causes of Occlusive AMI versus Non-Occlusive AMI.
Describe Mesenteric Venous Thrombosis specifically.
- AMI
- 40-70% mortality due to necrosis, perforation, and sepsis
- 70% fatality if diagnoses > 24h after onset
- Occlusive AMI
- Causes
- 50% caused by SMA embolus (i.e. a fib, endocarditis)
- 15-25% of cases caused by arterial thrombosis (i.e. CHF, PAD, CAD)
- Vasospasm in intestinal vessels
- Mesenteric vessel occlusion due to intestinal torsion from strangulated hernia or volvulus
- Causes
- Non-Occlusive AMI
- Lead to: bowel ischemia or infarction due to decreased mesenteric blood flow
- Causes
- Low CO
- Hotn (MAP < 45)
- Shock causes non-occlusive vasoconstriction of the splanchnic vasculature (liver, pancreas, spleen, gut circulation)
- Small intestine can compensate for decreases in up to 75% of blood flow, but only for a max of 12h
- Vasopressors, esp at max doses
- Mesenteric Venous Thrombosis
- Less common (15-25%)
- Causes
- Hypercoagulability, abd trauma, intra-abdominal hypertension, vasculitis, pancreatitis, cirrhosis, IBD
- Intravascular volume loss d/t surgery, intra-abdominal infections, oral contraceptives, smoking
Describe your patient’s classic AMI presentation.
How about abd exam?
- AMI Presentation:
- Sudden onset of severe abdominal pain
- Pain is out of proportion to the patient’s abdominal exam
- Pain is typically periumbilical area or epigastrium.
- Abdominal exam:
- Diffuse, non-specific tenderness without peritoneal signs such as guarding or rebound tenderness.
- GI bleeding occurs late in the disease process
Your patient with AMI commonly has involvement of which regions of the mesenteric vasculature?
Describe the patho and potential impact
- Location(s) of ischemia:
- Commonly, “watershed” regions are involved.
- Watershed regions are supplied by the distal ends of two major arteries.
- The rectum, rectosigmoid junction, splenic flexure, and left colon, which are supplied by both the SMA and IMA.
- During hypovolemia or hypoperfusion, watershed areas are susceptible to ischemia
- The abrupt decrease in blood flow to these portions of the large intestine leads to abdominal pain, which may be located in the left side
- If the entire thickness of the bowel wall is involved, bowel perforation and peritonitis can occur
Your patient with chronic mesenteric ischemia is likely to have what risk factors?
What portion of the bowel is usually affected?
What is the patho/progression of the disease?
When do symptoms usually occur, and what are the symptoms?
- Patients with CMI typically have wide-spread atherosclerotic disease, including CAD
- Risk factors include: Smoking, DM, HTN, and HLD
- CMI typically affects the small intestine
- Patho/progression:
- Inflammation occurs over a period of time
- Collateral circulation develops
- Symptoms occur when two of the three major arteries are affected
- Symptoms
- Symptoms occur gradually and may include abdominal pain, nausea, vomiting, and may progress to gastrointestinal bleeding
- Pain after eating (typical onset is between 10-180 minutes after eating), due to the need for increased post-prandial intestinal blood flow
- Pain can lead to fear of eating (sitophobia) and weight loss.
Describe your diagnostic process for mesenteric ischemia.
What should give you a particularly high index of suspicion?
Labs?
Lab findings?
Imaging?
Imaging findings?
- Diagnosis
- Mesenteric ischemia is often a diagnosis of exclusion
- Early diagnosis and intervention decrease mortality.
- Have a high index of suspicion of AMI in patients with acute abdominal pain out of proportion to exam findings, especially those over age 60 with a history of vascular disease
- Some may have abdominal bruits
- Some may have decreased lower extremity hair growth
- May have weak peripheral pulses
- Lab tests:
- BMP, lactic acid, LFTs, CBC, PT, aPTT, LDH, and stool guiac
- Leukocytosis, metabolic acidosis, and elevated lactic acid levels are common as AMI progresses
- These lab values may be normal early in the course of AMI
- Imaging:
- Biphasic CTA (CT angiography) abdomen & pelvis with and without IV contrast is the most common test for definitive diagnosis
- Benefits: Non-invasive and are able to evaluate for multiple causes of abdominal pain and leukocytosis compared to angiography
- Non-contrasted scan allows for visualization of arterial calcification
- Arterial and venous phases (biphasic) help determine the presence of arterial and venous thrombosis
- CTA is 96% sensitive and 94% specific for detecting mesenteric ischemia
- Oral contrast is not needed to diagnose intestinal ischemia
- Findings
- CT scans can assess for bowel wall edema or intramural hemorrhage
- Reperfusion events are associated with bowel wall thickening and mesenteric fat stranding on CT
- Free fluid within the abdominal cavity is commonly found in patients with non-occlusive AMI
- Free air is an uncommon finding
- Biphasic CTA (CT angiography) abdomen & pelvis with and without IV contrast is the most common test for definitive diagnosis
Describe your initial treatment for acute mesenteric ischemia
- NPO, bowel rest initiated, nasogastric decompression
- Medical therapy includes smoking cessation, control of HTN, and administering statins and aspirin
- Goal is to restore adequate organ perfusion
- Isotonic IV fluids helps prevent worsening ischemia.
- If possible, avoid using vasoconstrictor agents to increase BP since they may worsen AMI due to decreased mesenteric blood flow.
- Inotropic therapy may improve hemodynamics by increasing stroke volume (SV) and cardiac output (CO).
- Broad-spectrum antibiotics (gram negative & anaerobic coverage) are indicated in patients with evidence of AMI due to the risk of necrotic bowel perforation and peritoneal contamination
- IV analgesia.
Describe definitive treatment for mesenteric ischemia
- Medical therapy is commonly used for non-occlusive disease
- Continuously infusing nitroglycerin, or other parenteral vasodilators may augment blood flow
- Continuous infusions of papaverine are administered into the mesenteric arteries with intra-arterial catheters placed during angiography to improve circulation to the gut
- Papaverine decreases arterial spasms, allowing for improved blood flow
- Patients without perforation or any absolute contraindications
- Administering thrombolytics within eight hours of the onset of abdominal pain may restore blood flow
- Patients with acute occlusion who present with acute abdominal pain, signs of peritoneal irritation, evidence of necrosis, and/or clinical deterioration
- Should have exploratory laparotomy with surgical embolectomy and/or bowel resection may be necessary depending on size of the clot(s) and the extent of the intestinal ischemia
- Post-operatively
- Patients are anticoagulated with either low-molecular weight (LMWH) or unfractionated heparin (UFH)
- Hypercoagulable patients may require life-long oral anticoagulation
- Patients with CMI can undergo angioplasty and stenting of the affected artery
- Signs of stent restenosis are similar to those patients have pre-treatment, including post-prandial pain
- Post-operatively, patients are at risk for bleeding, infection, deep venous thrombosis (DVT), and protracted ileus
- Patients who are post-bowel resection for AMI may require long-term parenteral nutrition (PN)
- Patients who have had significant amounts of bowel resected are at risk for diarrhea and malabsorption of nutrients.