The decision to operate will often depend upon clinical suspicion as there is no specific test (except angiography) for detecting ischemia. The first step may be laparoscopy which will identify most causes of peritonitis. If the diagnosis is still in doubt, the abdomen is opened through a long midline incision. In early cases the small intestine may appear healthy. Closer inspection reveals a loss of the normal glistening appearance of the serosa and absent pulsation in the mesenteric vascular arcades. As ischemia progresses, the bowel becomes pale, blue, and edematous. All too often, however, a massive infarction is found, ruling out any procedure except resection.
If the small bowel appears viable, the superior mesenteric artery is exposed. In the case of an embolus, a pulse will be felt in the root of the mesentery between the duodenum and the inferior border of the pancreas, and the distal vessels will be soft and normal. The patient is heparinized and a longitudinal arteriotomy is made. Catheter embolectomy is performed, taking care to avoid overinflating the balloon which can result in arterial rupture or intimal injury. After proximal and distal embolectomy, the arterial bed is flushed with heparinized saline, and the arteriotomy is closed with a fine vascular suture.
Once adequate arterial flow has been established and, if possible, documented by completion arteriography, the bowel must be inspected carefully to determine the need for resection. A 20- to 30-min period of watchful waiting after revascularization will often reveal adequate perfusion of segments initially thought to be non-viable.
Intraoperative assessment of intestinal viability remains an unsolved problem. Many techniques designed to determine adequate perfusion of the gut wall, including electromyography, pH recordings, fluorescein injections, and Doppler laser ultrasound, have been advocated, tried, and abandoned for reasons of practicality and cost. Most surgeons fall back on clinical judgment in deciding whether to resect ( Ballard etal 1993). The criteria usually employed for viability are the return of color and pulsation and the resumption of peristalsis in the injured segment. The difficulty is often resolved by resecting short bowel loops of doubtful viability, if the patient's general condition is satisfactory, and exteriorizing the ends. Primary anastomosis is dangerous in these circumstances and should not be attempted.
Thrombosis of the superior mesenteric artery in the presence of viable bowel may justify a reconstructive vascular procedure. Extensive thromboendarterectomy of the midaortic region, including the origins of the visceral vessels, has been advocated, although most surgeons would now prefer a bypass graft from the infrarenal aorta to the superior mesenteric artery using autologous saphenous vein. For the surgeon inexperienced in reconstruction of the visceral arteries (surely, the majority), it is safer, in case of doubt, to resect the gut rather than to attempt to revascularize it.
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