**8. Mesenteric ischemia**

**Figure 2.** Colonic pseudo-obstruction following cardiac surgery. The first patient (left) presented with increasing ab‐ dominal pain/distention, nausea and vomiting following mitral valve replacement. Abdominal CT showed massively dilated left colon with compressive effect on the surrounding small bowel. The pseudo-obstruction resolved with neo‐ stigmine therapy. The second patient (right) developed diffuse colonic dilatation following coronary artery bypass

Gastritis and esophagitis are among the more commonly seen gastrointestinal complications in the CTS patient population [32]. In addition to clinical symptoms and history, endoscopy is the most commonly utilized diagnostic modality [33, 34]. Although esophagitis is often as‐ sociated with gastro-esophageal reflux (GER), the most pressing concern for post-CTS pa‐ tients with GER is the potential for pulmonary aspiration and associated complications [35]. The etiology of gastritis is multi-factorial, with major contributing elements including mu‐ cosal hypoperfusion, previous history of gastric mucosal disorder, and the use of non-steroi‐ dal anti-inflammatory drugs [36, 37]. Management includes avoidance of hypotension and hypoperfusion, and aggressive management with H2-receptor blockers or proton pump in‐ hibitors. For postoperative patients with GER and high pulmonary aspiration risk, the main‐

tenance of 45 degree head-of-bed elevation is an important preventive measure [38].

Gastrointestinal bleeding is among the most common GIC following cardio-thoracic proce‐ dures. In one study, gastrointestinal bleeding constituted nearly 29% of all GIC-CTS [32]. In general, upper gastrointestinal bleeding occurs more frequently than lower gastrointestinal bleeding, with most hemorrhages (>90%) occurring proximal to the ligament of Treitz [5]. Patients with previous history of peptic ulcer disease may be at higher risk for developing an upper gastrointestinal perforation or hemorrhage following cardiac surgery, although

grafting. His pseudo-obstruction resolved promptly following emergent colonoscopic decompression.

**6. Gastritis and esophagitis**

358 Principles and Practice of Cardiothoracic Surgery

**7. Gastrointestinal hemorrhage**

Mesenteric ischemia (Figure 3) is a well known complication of CTS that usually occurs within hours to several days after surgery. The gastrointestinal tract is vulnerable to ische‐ mia because it is often unable to acutely compensate for systemic hypotension. Further, due to the potential for persistent vasoconstriction following the initial "low flow" state, gastro‐ intestinal ischemia may continue despite return of hemodynamic stability (i.e., non-occlu‐ sive mesenteric ischemia or NOMI). Intestinal ischemia may lead to complications such as mucosal sloughing, gangrenous changes of the bowel wall, and perforation. Mortality may exceed 65% for patients with acute mesenteric ischemia [8]. Early recognition of signs and symptoms of bowel ischemia and early intervention are integral to successful outcomes and lower mortality rates [50]. One of the earliest signs of mesenteric ischemia is abdominal pain out of proportion to physical examination findings [51]. However, this can be quite difficult to elicit in postoperative CTS patients as many are mechanically ventilated and sedated fol‐ lowing surgery. In the setting of high clinical suspicion, sigmoidoscopy or colonoscopy can aid in diagnosis of colonic ischemia [52]. The subsequent sections will discuss post-CTS mes‐ enteric ischemia as divided into two major pathophysiologic types: (a) "low flow state" sec‐ ondary to systemic hypoperfusion; or (b) thrombo-embolic events.

associated hemolysis, inflammatory cascade activation, the use of anticoagulation, the pres‐ ence of hypothermia, and the reduced end-organ perfusion. Further, cardiopulmonary bypass may be associated with increased gastrointestinal permeability and enhanced cytokine release,

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In the postoperative setting, inadequate blood flow to the intestines and subsequent intesti‐ nal ischemia/infarction can be associated with hypotension and/or cardiogenic shock [10]. In one study, patients with renal failure (Creatinine >1.4), prior myocardial infarction, and those requiring intra-aortic balloon pump support were at higher risk of developing mesen‐ teric ischemia secondary to "low flow" state [8]. Prolonged mechanical ventilation requiring high positive end-expiratory pressure (PEEP) can also result in hypotension and impaired cardiac output, leading to splanchnic vasoconstriction and hypoperfusion. Furthermore, high PEEP is associated with activation of the renin-angiotensin-aldosterone system and in‐ creases in catecholamine levels [54]. This, in turn, results in shunting of blood away from the gastrointestinal system, leading to mismatch between oxygen delivery and demand. Persis‐ tent deficit in oxygen delivery then leads to mucosal ischemia and damage. Moreover, dur‐ ing the process of tissue re-perfusion after restoration/normalization of adequate oxygen delivery, the persistent vasoconstrictive state of non-occlusive mesenteric ischemia (NOMI) may be seen [32]. Management of NOMI consists of restoration of adequate circulating intra‐ vascular volume, maintenance of adequate cardiac output, and selective angiographic ap‐ proaches utilizing intra-arterial vasodilating agent infusion therapy [55]. Surgery is reserved for cases requiring resection of necrotic bowel, exploration for suspected perforation, and/or

Mesenteric ischemia following cardiac surgery results from embolic disease secondary to macrovascular embolism or thrombosis, such as SMA embolus, or microvascular emboli, such as embolic cholesterol "showering" secondary to aortic manipulation. Septic emboliza‐ tion with occlusive phenomena has also been reported in cases of endocarditis following open heart surgery [56]. The size of the embolus may be an important prognostic factor. For example, patients with large vessel emboli may have better outcomes when compared to pa‐ tients with microvascular or "distal" emboli [8]. High index of suspicion is critical to optimal patient outcomes. If recognized promptly, occlusive emboli to the mesenteric circulation can be treated via either endovascular and/or open surgical approaches, with acceptable success rates [51]. Patients with hypotension, cardiogenic shock, and/or pump failure requiring in‐ tra-aortic balloon pump not only are at risk of significant intestinal hypoperfusion, but are also at risk secondary to embolization and thrombus formation which may further exacer‐ bate the original insult to the intestinal tract. Surgical therapy is indicated if the patient de‐ velops peritonitis, perforation, sepsis, and/or end-organ failure in the setting of elevated clinical suspicion [57]. Planned or "second look" surgery is warranted if ischemic (but nonnecrotic) bowel segments are noted at the conclusion of the initial procedure [58, 59]. Open

contributing to microcirculatory dysfunction and mucosal injury [32].

revascularization procedure.

**10. Embolic phenomena**

**Figure 3.** Abdominal CT scan of a patient who developed peritonitis several days after undergoing coronary artery bypass grafting. The study shows diffuse portal venous gas (left) and pneumatosis of the bowel and the mesentery (right). The patient underwent laparotomy with segmental resection of necrotic small bowel. A planned "second-look" laparotomy showed no further bowel necrosis and primary small bowel anastomosis was performed.
