Acute Mesenteric Ischemia Treatment & Management

Recognition of acute mesenteric ischemia (AMI) before permanent tissue damage occurs is the best way to improve patient survival, and only angiography or exploratory surgery makes early diagnosis possible. Experience with computed tomography (CT) and magnetic resonance angiography (MRA) is rapidly changing the therapeutic approach, allowing prompt laparotomy in patients with suspected AMI when expeditious formal angiography is not available. A second-look procedure is indicated whenever bowel of questionable viability is not resected.

After initial medical or surgical stabilization, patients with AMI typically have a prolonged inpatient recovery time. This is especially true when resection of necrotic bowel is performed. Such patients may need to be kept on nil per os (NPO) status, and they may be maintained on parenteral nutrition for some time. If sepsis is evident, liver abscess should be actively sought. During the inpatient stay, every effort must be made to find and, if possible, treat any predisposing cause(s) of AMI.

Inpatient medications include the following:

• Papaverine - For patients with arterial occlusive AMI or nonocclusive mesenteric ischemia (NOMI)
• Heparin - For patients who have mesenteric venous thrombosis (MVT) or have undergone revascularization
• Warfarin - For long-term treatment of patients with MVT or atrial fibrillation
• Broad-spectrum antibiotics and pain medications - For all patients
• Thrombolytics - For selected patients with embolic AMI

Because timing is essential in preventing bowel necrosis with its attendant severe morbidity and mortality, patients should be transferred only if the primary hospital lacks adequate services to diagnose and treat the patient. Patients should be optimally resuscitated before transfer. Appropriate services should be available at the receiving hospital.

Some experience with percutaneous endovascular interventions has been accumulated. In select cases, especially in isolated spontaneous dissection of the SMA, stent placement may offer the best option.^[11]

Resuscitation

Every effort should be made to improve patients’ cardiovascular status. Vasopressors should be avoided, because they worsen ischemia. Oxygen should be provided to maintain a saturation between 96-99%, by endotracheal intubation if needed. Fluid resuscitation is accomplished with isotonic sodium chloride solution, and blood products are provided as needed. Adequacy of resuscitation can be monitored by urinary output, central venous pressure, or Swan-Ganz pressure monitoring.

Insert a nasogastric tube, and optimize cardiac status by treating arrhythmia, congestive heart failure (CHF), or myocardial infarction. Start broad-spectrum antibiotics early. Provide pain control while maintaining stable blood pressure.

Infusion of papaverine and thrombolytics

Papaverine infused through the angiography catheter at the affected vessel is useful for all arterial forms of AMI. It relieves reactive vasospasm in occluded arterial vessels and is the only treatment of NOMI other than resection of gangrenous bowel.

Start an infusion of 30-60 mg/h after angiography, and adjust the dose for clinical response. Continue this for at least 24 hours. If the catheter slips into the aorta, significant hypotension can occur. Papaverine is incompatible with heparin.

Thrombolytics infused through the angiography catheter can be a life-saving therapy for selected patients with embolic AMI. Bleeding is the main complication. Thrombolytic administration is risky and should only be undertaken if peritonitis or other signs of bowel necrosis are absent.

The infusion must be started within 8 hours of symptom onset. If symptoms do not improve within 4 hours or if peritonitis develops, stop the infusion and perform surgery.

Angioplasty after thrombolysis

A very select group of patients who have atherosclerotic plaques at the origin of the superior mesenteric artery (SMA) after thrombolysis is eligible for angioplasty. Angioplasty is technically difficult because of the anatomy of the SMA. Restenosis rates are 20-50%.

Limited study findings indicate a definite role for angioplasty in the treatment of AMI. A case of successful transcutaneous catheter aspiration of an SMA embolic clot was reported from the Czech Republic.^[12]

Heparin anticoagulation

Heparin anticoagulation is the main treatment of MVT. If no signs of bowel necrosis exist, the patient may not even need an operation. Heparin may increase the chance of bleeding complications. A possible avenue of study for future clinical trials is the use of enoxaparin or other low-molecular-weight heparins as a potential substitute for heparin in the treatment of MVT.

Administer heparin as a bolus of 80 U/kg, not to exceed 5000 U, and then as an infusion at 18 U/kg/h until full conversion to oral warfarin. Appropriate monitoring of anticoagulation using activated partial thromboplastin time (aPTT) is mandatory.

Before operative management of AMI, stabilize patients by means of intravenous (IV) fluid administration, antibiotic prophylaxis covering the colonic flora, nasogastric tube decompression, and bladder catheterization, with heparin or papaverine administered as indicated. Blood should be available.

In all types of AMI, resection of necrotic bowel may be required if signs of peritonitis develop. Differentiation of nonviable from viable bowel can be enhanced by intraoperative fluorescein administration. During laparotomy, 1 g of fluorescein is infused. Viable bowel fluoresces brightly under a Wood lamp, thus allowing the surgeon to better evaluate the segments that need resection.

Because of fat absorption, fluorescein can be used only once. Most patients can benefit from a 24- to 48-hour second-look operation to assess for viability of the remaining bowel. Intraoperative fluorescein administration may be performed either at the primary operation or during the second-look operation.

Embolic acute mesenteric ischemia

For embolic AMI, unless the involved bowel is clearly gangrenous, an attempt at reperfusion is necessary. The SMA is isolated, and the location of the blockage is determined by palpation of pulses. Because most emboli are near the origin of the middle colic artery, note the proximal SMA pulse in embolic AMI.

A transverse arteriotomy is made proximal to the point of occlusion, and a balloon-tipped Fogarty catheter (size 3 or 4) is passed distally. The balloon is then inflated and the clot extracted. The arteriotomy can be closed primarily or vein-patched to prevent lumen compromise. A bypass may be required if thrombectomy is unsuccessful.

Observe the intestines for 10-15 minutes after restoration of flow to assess viability of bowel. This can be enhanced by intraoperative duplex ultrasonography, fluorescein use, and palpation of pulses distal to the occlusion.

Thrombotic acute mesenteric ischemia

For thrombotic AMI, emergency surgical revascularization is indicated. Simple thrombectomy has little or no benefit, because most patients have clinically significant atherosclerosis at the time of the acute decompensation. Unlike patients with embolic AMI, these patients have a lesion at the origin of the SMA, and no SMA pulsation is detected at the origin.

If the gut is not gangrenous, proceed with revascularization. An antegrade aortomesenteric bypass is the best technique. Transaortic endarterectomy is an alternative when no vein is suitable for harvesting or when a prosthetic graft is contraindicated (eg, with massive fecal contamination).^[13] After revascularization and thrombectomy, reevaluate bowel viability.

Mesenteric venous thrombosis

For patients with MVT, as for any patient with AMI and signs of peritonitis, including diagnosed NOMI, exploratory laparotomy and resection of infarcted bowel is indicated.

Thrombectomy has little use in MVT, because it can only be performed if the thrombus is fresh (ie, no more than 1-3 days old). Thrombectomy has little proven effectiveness in this setting, because the thrombus is usually too widespread and all the thrombi cannot be removed completely.

Spontaneous dissection of superior mesenteric artery

When spontaneous dissection of the SMA is diagnosed before the onset of intestinal infarction, percutaneous stent placement has been successful.^{[4, 5, 6, 7]}

To prepare for surgery and to reduce oxygen demand on the ischemic bowel, patients must be on NPO status. No other specific dietary measures are mandatory.

Patients’ activities are dictated by their conditions. Bed rest to allow for monitoring and to reduce demand on cardiac output is balanced against ambulation to prevent DVT.

Aside from timely diagnosis and treatment of predisposing conditions, there are no known preventive measures for AMI. In the presence of a clinical syndrome suggesting chronic mesenteric insufficiency, color Doppler evaluation of the mesenteric vessels may help identify at-risk patients for further workup and identify those who might need angioplasty.

Consult a vascular surgeon to evaluate the patient and to perform a revascularization procedure if required.

Consult an interventional radiologist to perform any needed angiographic drug infusions or angioplasty.

Consult a critical care specialist to evaluate the patient for possible insertion of a Swan-Ganz catheter or admission to a critical care unit.

Patients who have had extensive small bowel resection have severe diarrhea for a few weeks, but many appear to be able to compensate for the reduced bowel length after a few months. Thereafter, they may have 1-3 liquid bowel movements a day and may maintain or gain weight with oral intake. On the other hand, patients who have undergone total resection of the small intestine need lifelong IV hyperalimentation (ie, total parenteral nutrition [TPN]).

A number of patients who recover from ileus secondary to intestinal ischemia may develop fibrosis of a segment of small bowel with intermittent partial obstruction.

Patients who have had MVT need warfarin therapy for at least 6 months or for life if a hypercoagulable state was discovered during treatment. Patients with atrial fibrillation should also be discharged on warfarin. Patients with other treatable predisposing conditions should be continued on appropriate therapy. Patients should be appropriately monitored in an anticoagulation clinic.

Outpatient medications include antiarrhythmics for patients with atrial fibrillation and warfarin for long-term treatment of patients with MVT or atrial fibrillation.