Several factors influence the low flow of intestinal loops, which can cause suffering and necrosis, a phenomenon called Acute Mesenteric Ischemia (AMI). Its etiopathogenesis may be related to occlusive phenomena of arterial, venous origin or even non-occlusive causes. Early diagnosis of this pathology directly impacts the patient’s prognosis, which is why mastery of the topic is essential for the recognition and effective management of IMA.
Diagnosis
Early identification of IMA requires a high degree of suspicion due to the various mechanisms that can trigger it, in addition to often nonspecific clinical and laboratory findings. Its diagnosis during hospital admissions occurs in 0.04-0.07% of adults, and is more commonly underdiagnosed when caused by non-ischemic mechanisms.
The presence of the following findings must be investigated: severe abdominal pain not compatible with physical examination, absence of other possible diagnoses for acute abdomen, concomitant cardiovascular diseases such as atrial fibrillation (arterial occlusion), previous venous thromboembolism (venous occlusion) or critically ill patients with history of shock (non-occlusive causes).
Laboratory findings such as elevated serum lactate can assist in the diagnosis, but normal levels do not exclude IMA.
Regarding age, although it occurs more frequently in patients > 70 years old, the diagnosis should not be ruled out in patients of other age groups if they have the above-mentioned risk factors.
If suspected, biphasic computed tomography angiography is indicated, and should not be delayed due to changes in renal function, as this identifies occlusions of the mesenteric vascular system, information that will enable early revascularization. Even in non-occlusive causes, CT angiography can provide relevant information regarding the viability of the intestinal loops, which will guide management as an indication for a surgical approach.
- Treatment
The primary objective is to restore intestinal perfusion, preventing the occurrence of irreversible damage. In all patients, one should seek to correct hypovolemia and optimize cardiac function with the aim of minimizing peripheral vasoconstriction. Additionally, oral or enteral food intake must be suspended to reduce local metabolic demand.
Immediate revascularization of the superior mesenteric artery (SMA) should be a priority if arterial occlusion is diagnosed. In stable patients with no signs of peritonitis, approaches such as angioplasty with combination of stents in thrombotic proximal occlusions, aspiration embolectomy in SMA embolic occlusions and thrombolysis with possible association of endovascular therapy may be indicated as initial therapy. In embolic causes, full anticoagulation must also be added, whereas in thrombotic causes, anti-aggregation and the use of statins are indicated.
In venous occlusions, treatment is preferably conservative. Full anticoagulation is the primary therapy in these cases. The use of antibiotic therapy is indicated in patients with peritonitis who will undergo resection of intestinal loops.
In non-occlusive causes, the use of vasodilators has shown potential benefit. Rigorous sequential clinical assessment associated with parameters such as serum lactate, intra-abdominal pressure and signs of organic dysfunction should guide the indication of surgical intervention in these patients.
Laparotomy with resection of intestinal loops is indicated in cases of transmural necrosis. It can be identified by radiological findings (pneumoperitoneum, intestinal pneumatosis or absence of mural enhancement) or clinical findings (instability, lactate changes or abdominal compartment syndrome). If the magnitude of necrosis is not well defined in the first approach, a second look with delayed closure of the abdominal cavity to assess the need for subsequent intestinal resections.
What to take home
In IMA, time means viable intestine, so it is important to have a high degree of suspicion in patients with compatible risk factors or clinical history. Performing abdominal CT angiography provides relevant information and helps define the initial therapeutic approach, differentiating occlusive from non-occlusive causes. In addition to diagnosis, it is essential to perform volume adjustment, optimize cardiac function and rigorously reevaluate the patient’s clinical evolution, identifying signs that indicate surgical intervention.
