In the absence of obvious peritonitis, surgeons must consider the patient’s clinical history, physical examination, laboratory results, and imaging findings before deciding whether operative management is appropriate in a patient with PI (Table 13.1). Patient characteristics that are associated with pathologic PI are age greater than 60 [3, 5] and comorbidities that increase the chance of a thromboembolic event, including smoking, diabetes, hypertension, hyperlipidemia, coronary artery disease, and stroke [4, 7]. Furthermore, patients who are at risk for developing a low flow state secondary to arrhythmias, heart failure, or vasopressor dependence are also more likely to have bowel ischemia. Physical examination findings include abdominal tenderness. Specifically, diffuse peritonitis with involuntary guarding and rebound tenderness is an important clinical sign that suggests the need for emergent exploration [1, 3, 4, 7]. Hypotension refractory to intravenous fluids or dependence on vasopressors is another indicator that surgery is necessary [3]. Tachycardia, tachypnea, and abdominal distension may be other less sensitive signs [3, 7]. Laboratory findings suggestive of bowel ischemia include a lactate greater than 2.0 mmol/L [1–3, 5–7], acidosis with bicarbonate less than 20 mmol/l [1, 3, 5], and leukocytosis greater than 12 c/mm [3, 5]. With regard to radiographic signs, the presence of portal venous gas [1, 2, 8–10], dilation of small bowel greater than 3 cm and large bowel greater than 6 cm, mesenteric stranding, and ascites all point toward ischemic and/or gangrenous bowel [1, 7, 11]. Regardless of which signs and symptoms are present, the decision for or against operative management must be timely as mortality rate is high in the setting of pathologic PI.

Once the decision to explore the abdomen has been made, much of the intraoperative plan can be determined preoperatively by knowing the source of ischemia. The most common causes of acute mesenteric ischemia leading to pneumatosis are arterial embolism, arterial thrombosis, nonocclusive mesenteric ischemia, and venous outflow obstruction or mesenteric venous thrombosis (Table 13.2).