Acute Intestinal Ischemia in the Elderly

Case Presentation

Mrs. S, an 81-year-old woman who had previously resided in an assisted living facility, is living in a nursing home for rehabilitation following a hip fracture, which occurred several weeks ago after slipping on ice. Past medical history includes congestive heart failure (ejection fraction = 0.25), hypertension, hypercholesterolemia, mild chronic renal insufficiency (creatinine 3.4 mg/dL), and early-stage dementia. Her medications include furosemide, lisinopril, atorvastatin, isosorbide dinitrate, and donepezil.

For several weeks prior to falling, Mrs. S had been experiencing postprandial abdominal cramping, and thus had reduced her food intake, resulting in a 5-pound weight loss during this time. She underwent an open reduction internal fixation and had no postoperative complications. She has done well with her rehabilitation and is ambulating without difficulty.

After eating, she again is experiencing abdominal cramping, which the nursing staff attributes to gas. She is scheduled to return home in a few days.

The night before discharge, she is found in her bed, vomiting and writhing in pain, pointing to the peri-umbilical area. Vital signs include a temperature of 99 degrees F, blood pressure 90/70 mmHg, respirations 32, and pulse rate 115.

Mrs. S is transferred to the local emergency department, where the abdominal examination reveals mild distension, diminished bowel sounds, minimal diffuse tenderness, with rebound tenderness. Her white blood cell count is elevated at 18,000 with 10% bands. The BUN is elevated at 54, and the creatinine 3.9 mg/dL. An urgent radiological procedure is considered, but because of renal insufficiency, an exploratory laparotomy is performed

Discussion

Intestinal ischemia (mesenteric ischemia) is a result of reduced blood flow to the bowel, with resulting injury to the bowel from hypoxemia, with associated nutrient deficiency.

The splanchnic circulation supplies the small bowel and colon via the superior mesenteric, inferior mesenteric, and hypogastric arteries. Because there is extensive collateralization between these arterial supplies, ischemic disease will only occur if there has been significant compromise in two of the three main arterial trunks. Further protection against ischemic injury results from a network of intramural submucosal vessels, which help to preserve parts of the bowel even when the extramural arterial supply has been interrupted.¹ During an ischemic event, the intramural blood supply is redistributed to help preserve the mucosa.²

Intestinal ischemia can be acute or chronic, involving an artery, arteriole, vein, or venule, and can be located in the small or large bowel. The condition can be further categorized as occlusive (embolic or thrombotic) and non-occlusive (ischemic). Mrs. S most likely suffered an acute ischemic event in a background of chronic mesenteric insufficiency.

Chronic mesenteric insufficiency (intestinal angina) is almost always a result of decreased blood flow due to atherosclerosis of the proximal mesenteric arteries. At least two of the major splanchnic vessels are occluded in over 90% of patients, and all three in over 50%.³ Patients typically present with postprandial abdominal pain. At first, the pain may be minimal, usually after a large meal, and can last for several hours. Over time, the pain can become more severe and incapacitating, peaking and receding over several hours, and results in fear of eating because of the anticipation of pain. Steatorrhea occurs in about 50% of patients. Ultimately, most patients experience a significant weight loss.⁴

Some patients with acute superior mesenteric artery occlusion may have an ileus, but no rectal bleeding, and thus the diagnosis may be delayed, especially in patients in intensive care units or with other medical problems. On careful physical examination, these patients may show signs of peritoneal irritation. Diagnosis is made by clinical history, often more difficult in a nursing home setting, especially if the patient has a history for dementia.

Acute mesenteric ischemia, with resulting bowel infarction, is the most serious complication of chronic mesenteric insufficiency. Patients generally present with sudden and severe periumbilical pain, followed by nausea and vomiting. The classic teaching of “pain out of proportion to findings on physical examination” is frequently observed in the early stages of acute mesenteric ischemia, especially in elderly patients. The abdominal examination might indeed be normal. In the older adult, acute mesenteric ischemia more frequently presents with nonspecific symptoms, such as mental status changes (29%) and tachypnea (35%), whereas abdominal pain is seen less often than in the younger patient.⁵

Ultimately, patients develop abdominal distension and abdominal tenderness with rebound and guarding, the repetitiveness of which is a result of the degree of intestinal ischemia. Leukocytosis, ileus, hematemesis, and back pain are commonly seen, followed by hypotension and shock. Approximately 75% of patients with acute mesenteric ischemia will have occult bleeding, as gross bleeding is rare in this situation, although its presence would indicate right colon involvement.³

Acute mesenteric ischemia has several etiologies, but regardless of the cause, if the patient has inadequate collateralization, it is a lethal disease in the older population; thus, it is critical that the diagnosis be made early, before irreversible and catastrophic acute infarction of the small bowel results.

Superior mesenteric artery embolism is the most common cause of acute mesenteric ischemia, accounting for approximately 50% of all cases. It generally results from ventricular or left atrial thrombi, often in the setting of atrial fibrillation in patients who are not adequately anticoagulated, or in patients with valvular heart disease. Concomitant peripheral emboli are seen in 20% of patients.³

Non-occlusive mesenteric ischemia accounts for approximately 25% of cases of acute mesenteric ischemia. It results from vasoconstriction, a protective mechanism in low flow states to allow shunting of blood to vital organs, in settings such as congestive heart failure and arrhythmias, resulting in a low flow state, as well as in hypovolemic states associated with burns, pancreatitis, hemorrhage, and sepsis. Patients with cirrhosis and end-stage renal failure on dialysis are also at risk.⁴ Fortunately, non-occlusive mesenteric ischemia is seen less often as a result of improved capabilities of monitoring hemodynamic parameters in the intensive care setting, as well as the use of vasodilators in the management of congestive heart failure and myocardial infarction.

Superior mesenteric artery thrombosis accounts for 10% of cases of acute mesenteric ischemia, is found most commonly in the setting of severe atherosclerotic disease, and often is preceded by symptoms consistent with chronic mesenteric insufficiency, as has occurred in the case presented here. Risk factors include older age; low output states, such as in congestive heart failure or dehydration; and recent myocardial infarction associated with hypotension. The overall mortality rate is high, at 71%, although if the condition is diagnosed and treated within 24 hours survival rates improve.⁶

Mesenteric venous thrombosis can present acutely, subacutely, or chronically. The superior mesenteric vein is most often involved. Most of these patients are younger. Predisposing factors include inherited or acquired hypercoagulable states, use of oral contraceptives, portal hypertension, recent abdominal surgery, and trauma.⁴

Focal segmental ischemia, involves only short bowel segments, with generally reasonable collateral flow, thus limiting the degree of transmural bowel necrosis. Usually not life-threatening, it is a rare (5% of cases) cause of acute mesenteric ischemia.

Diagnosis and Treatment
Acute mesenteric ischemia is diagnosed with selective mesenteric angiography, with a sensitivity in five of six studies between 90% and 100%, and a specificity reported in two studies of 100%.^2,5 One disadvantage of traditional angiography is its potential for renal toxicity, especially in the elderly with reduced renal blood flow due to atherosclerosis. Although computed tomography (CT) angiography has been shown to be promising as a method for diagnosing acute mesenteric infarction, it is not as sensitive or specific as standard angiography and has the disadvantage of not allowing treatment with intra-arterial vasodilators.⁷ Doppler ultrasound or CT scanning can demonstrate the normal increase in splanchnic blood flow after eating, and in patients with chronic mesenteric insufficiency, a significant decrease or even absence of blood flow in the major mesenteric arteries after eating can be demonstrated.⁸

When the patient is diagnosed with acute mesenteric ischemia, volume rehydration is critical. Underlying etiologies such as atrial fibrillation or congestive heart failure must also be treated.3 Usually, intravenous antibiotic coverage for gram-negative and anaerobic organisms should be given.⁵ At least one study suggests that coverage for anaerobes may be more important in treatment and outcomes.⁹ 

Thrombolysis or immediate surgery are the only options for preventing or treating bowel infarction. Thrombolysis has been successful in treating superior mesenteric artery emboli and, to some extent, thrombi. Agents currently in use include streptokinase, urokinase, and tissue plasminogen activator.¹⁰ Treatment of acute occlusive mesenteric ischemia is governed by the presence of peritoneal signs. If present, exploratory laparotomy is indicated.

Once the vascular anatomy is understood and the cause of the occlusion is defined (embolic vs thrombotic), several surgical procedures are possible. These include resection of necrotic and perforated bowel with thrombo-embolectomy, patch angioplasty, endarterectomy, or bypass procedures.¹¹ In the unfortunate setting of bowel perforation, peritoneal lavage with saline and antibiotics must be undertaken. Many of these patients go on to “second-look” surgery.¹² In patients with chronic ischemic bowel disease, with postprandial abdominal pain, steattorhea, and progressive weight loss, arteriography followed by revascularization of affected bowel is reasonable.¹³

Outcome of the Case Patient

Mrs. S underwent exploratory laparotomy, at which time a small segment of her bowel was found to be infarcted, with no evidence of perforation. Resection was performed, and after a lengthy recovery, she returned home.

The author reports no relevant financial relationships.