Bowel necrosis is a late stage finding of several different disease processes characterized by cellular death due to reduced blood flow to the gastrointestinal (GI) tract. This serious and often fatal condition can be secondary to vascular occlusion, bowel inflammation, obstruction, or infection. In infants, it is known as necrotizing enterocolitis and is thought to be due to bacterial overgrowth in the setting of an underdeveloped immune system. In adults, the most common cause of bowel necrosis is an acute mesenteric occlusion, and less commonly, perforations, chronic ischemia, inflammatory disease, and other mechanical obstructions. Bowel necrosis is a late stage finding of decreased blood flow to the GI tract and is frequently accompanied by septic shock. The prognosis is poor, and the reduction in mortality relies on early identification and intervention.
The most common causes of bowel necrosis are acute arterial obstruction from a thrombo-embolism with underlying atrial fibrillation, through a patent foramen ovale, or from frank perforation and bacterial invasion. Less common causes are venous thrombosis, chronic ischemia, autoimmune disease, mechanical obstruction and non-obstructive mesenteric ischemia. These conditions are typically seen in patients with severe vascular pathology and other comorbidities and are theorized to be a combination of infectious agents, inflammatory mediators and reperfusion injury leading to ischemia, perforation, and bowel necrosis.
Bowel necrosis is the end stage of several different disease processes making an accurate determination of prevalence difficult. One of the most common causes of bowel necrosis, acute ischemic bowel, is a rare disease accounting for only .09% to .2% of surgical admissions. About 50% of cases are due to embolic events, 30% due to plaque rupture, 10% to 20% from venous obstruction and less than 5% due to dissection, vasospasm, and inflammation.
Bowel necrosis is the widespread cellular death of any part of the GI tract below the stomach. It is due to the body’s inability to meet the metabolic demands of the tissue. The cells, starved of oxygen, switch to anaerobic metabolism which does not provide enough energy to maintain the electrochemical gradient and hydrostatic equilibrium resulting in swelling and rupturing of cells. Physiologically, this results in bowel edema and breakdown of the immunological barrier permitting bacteria to invade the dying tissue. Once inside the bowel tissue, they begin to produce proinflammatory mediators resulting in further damage and edema. Initially, cells furthest from the blood supply die first, and as time passes, the entire thickness of the bowel wall dies and becomes necrotic. Bacteria, toxins, and breakdown products return to systemic circulation resulting in systemic inflammation and sepsis.
This cascade is usually precipitated by a low-flow state such as an acute embolic, thrombotic, inflammatory, or obstructive event.
History and Physical
For patients in the early stages of the disease process, history is crucial for determining the underlying etiology since vital signs and physical exam may not reveal the diagnosis. Up to one-half of patients will have a history of embolic diseases such as deep vein thrombosis (DVT) and pulmonary embolism (PE), or history of atrial fibrillation. They will also frequently have a preceding history of post-prandial pain, loss of appetite, nausea/vomiting and unintentional weight loss.
Patients with bowel necrosis secondary to perforation and bacterial invasion will likely have a history of risk factors predisposing to perforation such as peptic ulcer disease, alcoholism, heavy NSAID use, inflammatory bowel disease (IBD) or steroid use with acute onset of abdominal pain. Their exam will be concerning for evidence of an acute abdomen, fevers, nausea, and vomiting with progression to sepsis and septic shock without intervention.
Lastly, there are a variety of less common precipitators of bowel necrosis, though most of them cause either an acute or chronic low flow state. These patients typically have vascular risk factors such as diabetes, peripheral vascular disease, or smoking. They will present with acute on chronic pain, diffuse abdominal pain, and signs of sepsis or septic shock.
Description of the type and severity of abdominal pain depends on several factors including the cause of ischemia, affected vasculature, and comorbidities. Acute arterial obstruction of the superior mesenteric artery will present with severe, periumbilical pain with nausea and vomiting. Chronic mesenteric ischemia will present with progressively worsening post-prandial abdominal pain with appetite and weight loss. Venous thrombosis is subtle with waxing-and-waning non-specific pain. Lastly, nonocclusive mesenteric ischemia has a variable presentation and generally co-exists with other serious disease processes such as peripheral vascular disease (PVD), congestive heart failure (CHF), or dialysis-dependent renal failure.
On physical exam, patients will appear in distress and diaphoretic. Their abdominal exam can vary from severe pain out of proportion to physical exam findings to an acute rigid abdomen with peritonitis.
Evaluation of the patient with bowel necrosis must proceed quickly with a high degree of suspicion. As with any critically ill patient, a rapid evaluation of their airway, breathing, and circulation while establishing intravenous (IV) access and hemodynamic monitoring is essential upon presentation. Definitive airway management may be indicated, but blood pressure should be optimized prior to intubation. Often, the underlying etiology of the patient’s shock is unclear, and a bedside RUSH ultrasound exam, ECG, portable chest x-ray, basic metabolic panel (BMP), and arterial blood gas (ABG) can be used to quickly evaluate for cardiogenic, hypovolemic, obstructive or distributive shock and help narrow the differential. Further laboratory evaluation should include a complete blood count (CBC), complete metabolic panel, INR, blood cultures, PTT and lactic acid.
If the patient remains hemodynamically unstable despite adequate resuscitation, the patient should be taken to the operating room emergently for exploratory laparotomy. Otherwise, a stat CT of the abdomen and pelvis with IV contrast should be ordered to evaluate for cause and extent of ischemia or necrosis. Radiological evaluation should not be delayed while awaiting laboratory results and the benefits of contrast outweigh the risk of any nephropathy in these critical patients. Often, the bowel will have air within the wall referred to as pneumatosis intestinalis and suggests a breakdown of protective mechanisms and bacterial invasion. Another sign is gas in the portal vasculature. One meta-analysis found the sensitivity and specificity of a contrasted CT scan for acute mesenteric ischemia to be 93.3% and 96%, respectively. If the diagnosis remains unclear, angiography is recommended and can reveal filling deficits or stenotic arteries.
Patients with bowel necrosis can present with a variety of symptoms secondary to the underlying etiology of their disease, varying from severe abdominal pain to altered mental status and septic shock. The differential should include sources of infection such as pyelonephritis, cholangitis, diverticulitis, causes of shock including septic, cardiogenic, hemorrhagic, and distributive as well as causes of bowel necrosis such as acute versus chronic ischemia, perforation, thrombotic emboli, and obstruction.
In patients with this disease process, who receive adequate and appropriate treatment including timely operative intervention, mortality remains exceedingly high. Bowel necrosis without appropriate intervention and surgical management carries mortality approaching 100%. The pooled, operative mortality rate for acute mesenteric ischemia has been reported at 47%, and patients who survive the initial event have a high probability of post-operative complication.
Bowel necrosis can have many complications. Sepsis associated with bacterial overgrowth can cause hypotension and end-organ damage, particularly renal and hepatic failure. Patients requiring emergency surgery can have post-operative infections and obstructions. For those who survive the initial intervention, mortality remains elevated secondary to underlying comorbidities and frequently results in long-term disability.
Emergent consultation with radiology, anesthesiology and surgery is required to coordinate interpretation of imaging and surgical intervention.
Enhancing Healthcare Team Outcomes
Bowel necrosis is a surgical emergency with poor outcomes even with early recognition, resuscitation and surgical intervention. Due to the rarity of the condition, there are no Level I recommendations for evaluation and management, and those that do exist are based on case series, reviews, and small studies. The current recommendations call for high clinical suspicion in patients with "abdominal pain out of proportion" and risk factors, followed by prompt evaluation with CT angiography with aggressive resuscitation and surgical intervention. (Level III). The prognosis depends on the amount of bowel involved, other comorbidities, age and presence of shock. Resection of large amount of bowel can also leave a patient with short bowel syndrome.