Intestinal ischemia can affect the small intestine or the colon. Whereas, “colonic ischemia” refers to ischemia that affects the colon, “mesenteric ischemia” refers to ischemia that affects the blood vessels of the small intestine. It can be secondary to occlusive or nonocclusive obstruction of the arteries or can be caused by obstruction of venous outflow.
The major etiologies of mesenteric ischemia are as follows:
Mesenteric Arterial Embolism
Emboli generally lodge in the superior mesenteric artery (SMA), which supplies the small intestine. This causes an acute onset of pain. Predisposing factors include cardiomyopathy, atrial fibrillation, recent angiography, underlying vasculitis and valvular disorders.
Mesenteric Arterial Thrombosis
Acute arterial thrombosis is usually a result of atherosclerosis, either secondary to acute plaque rupture, or gradual build-up until there is critical stenosis. Predisposing factors include patients with atherosclerosis, peripheral arterial disease, hypercoagulability, estrogen therapy, and prolonged hypotension.
Mesenteric Venous Thrombosis
Mesenteric venous thrombosis causes increases in the resistance of mesenteric venous blood flow. Patients who have local intra-abdominal inflammatory processes (such as inflammatory bowel disease) are at higher risk for this. Patients who are hypercoagulable (in other words those with heritable and acquired thrombophilias and malignancies) are also at a higher risk.
Nonocclusive Mesenteric Ischemia (NOMI)
These cases usually involve a “spasm” of the SMA, which can ultimately cause hypoperfusion to the small intestine and colon. Risk factors include peripheral artery disease, septic shock, vasoconstrictive medications (such as digoxin), cocaine abuse, hemodialysis, among many other conditions.
Mesenteric ischemia is rare. It is thought to have a prevalence of 0.09% to 0.2% of all hospital admissions in the United States, although the exact percentage is truly unknown. Below is the estimated prevalence of each etiology of mesenteric ischemia:
Usually, mesenteric ischemia is seen in elderly patients, especially those with cardiovascular disease. In younger patients who have no known cardiovascular disease, venous thrombosis is the main cause of mesenteric ischemia.
The arterial supply to the intestines consists of the SMA and the inferior mesenteric artery (IMA). The venous system parallels the arterial circulation (drains into the body’s portal venous system). The superior mesenteric artery supplies most of the small intestine, whereas the inferior mesenteric artery supplies the colon. The celiac artery (which mostly supplies the liver and spleen) provides collateral blood flow to the small and large intestines.
Mesenteric ischemia can be either acute or chronic and can be caused by arterial emboli, arterial thrombi, venous thrombi, or vasospasm of the mesenteric artery. No matter the etiology, ischemic injury occurs when there is not enough oxygen delivery required for cellular metabolism. However, intestinal injury occurs when there is tissue hypoxia, followed by reperfusion. Thus, mesenteric ischemia not only inflicts injury via hypoperfusion but through reperfusion as well. This multifactorial response, characterized by free radicals, toxic byproducts, and neutrophil activation results in multisystem failure.
It is important to obtain a thorough personal and family history for patients who may have mesenteric ischemia. Patients with acute embolic mesenteric ischemia have a history of a prior embolic event about 30% of the time. Also, those with acute mesenteric venous thrombosis have a personal or family history of deep vein thromboses or pulmonary emboli roughly 50% of the time.
The most common presenting symptom is abdominal pain. The patient’s symptoms and presentation may help determine the etiology of the ischemia. An arterial embolism usually causes sudden, severe, periumbilical pain and is associated with nausea and vomiting. Thrombotic mesenteric arterial occlusion is usually associated with pain that is worse after eating. Patients with mesenteric venous thrombosis usually have slower-onset, “waxing and waning” abdominal pain.
The physical exam may be normal. In fact, patients present with pain that is out of proportion to the initial physical exam. There may be mild distension present, but peritoneal signs only begin to show when transmural bowel infarction and necrosis develops.
The gold standard for diagnosis of mesenteric ischemia is mesenteric angiography. However, computed tomography (CT) angiography is a sufficient initial diagnostic modality. Lab tests, including white blood cell count, d-dimer, and lactate can aid in the diagnosis of mesenteric ischemia, but clinicians should not solely rely on these tests. In fact, lactate and d-dimer are not very specific. A thorough history and physical examination, along with serial abdominal exams, are more important.
Patients with acute mesenteric ischemia usually need immediate surgical intervention. Treatment should begin promptly in the emergency department with aggressive fluid resuscitation and broad-spectrum antibiotics (with coverage for bowel flora). If the patient remains hypotensive despite aggressive fluid resuscitation, a norepinephrine drip should be started. However, vasopressors can technically worsen ischemia and should be used with caution.
Mesenteric arterial occlusion from an embolism is treated with early surgical laparotomy with embolectomy. Although still being researched, some patients with a very early diagnosis of mesenteric arterial embolism (without signs of peritonitis) can be treated with local infusion of a thrombolytic agent. Mesenteric arterial thrombosis usually needs surgical revascularization or stenting. Mesenteric venous thrombosis can sometimes be managed medically with systemic anticoagulation, but it is dependent upon disease severity. Treatment of NOMI aims to eliminate the underlying cause that is causing the ischemia, for example, removing the vasoconstrictive medications that are causing the mesenteric artery to spasm.
As long as there are no contraindications, patients are usually treated with systemic anticoagulation after surgical intervention.
Mesenteric ischemia can present in many different ways, and initially has very nonspecific physical exam findings. It is important to keep the diagnosis at the top of the differential diagnoses, especially in elderly patients with risk factors. Differential diagnosis includes:
Mortality is estimated to be 60% to 80%, especially in those with more than a 24-hour delay in diagnosis. Surgical intervention within 6 hours of symptom onset increases survival rates. In general, prognosis depends on the etiology. Patients with an arterial etiology have worse survival outcomes than those with a venous etiology.
Mesenteric ischemia can have many complications. If mesenteric ischemia is not treated in time, complications include:
Patients with acute mesenteric ischemia require intensive care and should be placed in the hospital’s intensive care unit after surgery. Most patients require a “second-look laparotomy” 24 to 48 hours after mesenteric revascularization, as it is important to re-evaluate the bowel. Unless contraindicated, patients should be on long-term systemic anticoagulation after their hospital stay. If a mesenteric artery stent is placed, it is important to have periodic surveillance of the stent (either with duplex ultrasound or CT angiography), although there have been few studies done on specific surveillance intervals.
If the diagnosis is suspected in the emergency department, General Surgery should be consulted promptly. Vascular surgery and interventional radiology can also be consulted, but this depends on the hospital’s available services. Palliative medicine can be consulted for poor surgical candidates with extensive infarction.
Always keep mesenteric ischemia at the top of the differential diagnosis in patients, especially the elderly ones with risk factors and co-morbidities. Summary and clinical pearls are as follows:
The management of mesenteric ischemia is multidisciplinary. Many of these patients have other comorbidities and need to be assessed by other health professionals. Because of the presence of vascular disease, the other organ systems in the body also need to be closely monitored. For those who have atrial arrhythmias, the patients need long-term anticoagulation. In addition, the pharmacist must ensure that a therapeutic INR has been achieved. Periodic anticoagulation profile is mandatory. The patient should be urged to stop smoking and ensure that the blood pressure is adequately controlled. Many patients may develop diarrhea as a result of bowel resection and may develop malabsorption. Thus, a dietary consult is recommended. In some patients, long-term intravenous hyperalimentation may be required. Finally, patients who end up with a stoma will need to be seen by a stoma nurse. (Level V)
Even though survival of patients following mesenteric artery ischemia has improved over the past 3 decades, the disorder still carries a very high morbidity and mortality. Depending on the time of presentation and treatment, the mortality can approach 10-80%. Even those who survive are left with a risk of re-thrombosis, short bowel, a colostomy or ileostomy. Many patients are left with a short gut and require long-term parenteral nutrition. The outcomes are usually worse in seniors, those with other comorbidities, sepsis and metabolic acidosis at the time of presentation. Early recognition of the problem can help reduce the mortality. (Level V)