acute mesenteric ischemia Flashcards
What is acute mesenteric ischemia (AMI)?
A life-threatening condition caused by reduced blood flow to the intestines, leading to bowel ischemia and necrosis.
What are the four main types of mesenteric ischemia?
1) Embolic occlusion (most common), 2) Arterial thrombosis, 3) Non-occlusive mesenteric ischemia (NOMI), 4) Mesenteric venous thrombosis (MVT).
Which vessel is most commonly affected in acute mesenteric ischemia?
Superior mesenteric artery (SMA), due to its large territory of bowel supply.
What are common risk factors for AMI?
Atrial fibrillation, atherosclerosis, recent MI, heart failure, shock, hypercoagulable states (e.g., malignancy, factor V Leiden).
What is the classic symptom of acute mesenteric ischemia?
Sudden, severe abdominal pain that is disproportionate to physical exam findings.
What are late signs of bowel necrosis in AMI?
Peritonitis, abdominal distension, sepsis, and shock.
What are key lab findings in AMI?
Elevated lactate (metabolic acidosis), leukocytosis, and hemoconcentration.
A 75-year-old man presents to the emergency department with sudden-onset, severe abdominal pain that began six hours ago. He has a history of hypertension and hyperlipidemia. On examination, his abdomen is soft, and mildly distended, with diffuse rebound tenderness to palpation. Temperature is 37.5°C (99.5°F), blood pressure is 94/62 mmHg, pulse is 122/min and irregular, respiratory rate is 22/min, and oxygen saturation is 98% on room air. Laboratory findings are significant for leukocytosis, and a lactate of 5.4 mmol/L. ECG is significant for atrial fibrillation with rapid ventricular response. IV fluids and broad-spectrum antibiotics are initiated. Abdominal x-ray reveals findings consistent with pneumatosis intestinalis within the ascending colonic bowel wall. What is the most appropriate next step in management?
In addition to stabilization with IV fluids and broad-spectrum, emergent surgical consultation for exploratory laparotomy is needed for unstable patients with suspected acute mesenteric ischemia with pneumatosis intestinalis, given the high risk for bowel necrosis. This patient presents with sudden, severe abdominal pain disproportionate to examination findings, tachycardia, hypotension, and new-onset atrial fibrillation. These signs and symptoms, combined with elevated lactate levels and pneumatosis intestinalis on abdominal X-ray, strongly suggest a diagnosis of acute mesenteric ischemia (AMI), a life-threatening abdominal process. The patient’s acute onset of symptoms, in the setting of underlying atrial fibrillation, points to an embolic source, which most commonly results in occlusion of the superior mesenteric artery. In addition, the presence of hypotension, elevated lactate levels and pneumatosis intestinalis indicates advanced ischemia and the potential for bowel necrosis. In addition to IV fluids and broad-spectrum antibiotics, emergent surgical consultation for exploratory laparotomy is the best next step in management for an unstable patient with suspected acute mesenteric ischemia. Another indication for emergent surgical consultation for exploratory laparotomy is the presence of pneumoperitoneum on abdominal imaging which can indicate bowel perforation. Early surgical intervention can identify nonviable bowel segments for resection and restore blood flow to salvageable bowel. Patients with AMl should also be made NPO, and have an NG tube inserted to decompress the bowel.
What radiographic finding strongly suggests advanced mesenteric ischemia?
Pneumatosis intestinalis (gas within the bowel wall), indicating impending bowel necrosis.
What is the gold standard test for diagnosing AMI?
CT angiography of the abdomen and pelvis, which can identify vascular occlusion and bowel ischemia.
Although a CT angiogram can identify the location and extent of vascular occlusion in acute mesenteric ischemia, a CT would be inappropriate in the presence of emergent conditions like acute peritonitis or pneumatosis intestinalis, both which are suggestive of advanced ischemia and impending bowel necrosis, making surgical intervention the priority. Obtaining a CT angiogram would delay emergent surgical intervention.
Why is lactate an important marker in AMI?
Elevated lactate indicates anaerobic metabolism due to ischemia, helping assess severity.
What is the first step in management for unstable AMI patients with peritoneal signs?
Emergent surgical consultation for exploratory laparotomy to assess bowel viability and resect necrotic segments.
When is intravenous heparin indicated in AMI?
For stable patients with embolic AMI without peritoneal signs, to prevent further clot propagation.
Intravenous heparin infusion can be used as a treatment option in the management of stable patients with acute mesenteric ischemia without signs of advanced ischemia. However, the presence of emergent conditions like pneumatosis intestinalis, which signify advanced ischemia, emergent surgical intervention is the priority.
When is thrombolytic therapy used in AMI?
For stable patients with embolic AMI who are not surgical candidates.
When is endovascular therapy (embolectomy or stenting) used in AMI?
For stable patients with embolic AMI, particularly if caught early before bowel necrosis.
Interventional radiology (IR) consultation for embolectomy may be considered in stable patients with acute mesenteric ischemia, particularly in those who are poor surgical candidates. The presence of emergent conditions like pneumatosis intestinalis indicates advanced ischemia and impending bowel necrosis, requiring emergent surgical consultation for exploratory laparotomy to assess bowel viability and resection of nonviable bowel segments, rather than IR.
What broad-spectrum antibiotics are recommended in AMI?
Carbapenems or piperacillin-tazobactam, to cover gut flora and prevent sepsis.
Why should patients with AMI be kept NPO?
To prevent bowel distension and worsening ischemia, and to prepare for potential surgery.
What is the most severe complication of untreated AMI?
Bowel necrosis leading to perforation, sepsis, and multi-organ failure.
What is the mortality rate of AMI if surgical intervention is delayed?
Up to 70%, emphasizing the need for rapid diagnosis and treatment.
