Enteral nutrition is regarded as a preferred route for nutrition support of the critically ill patient with functioning digestive tract. Enterally administrated nutritional support has been found to prevent mucosal weight loss, to increase endothelial proliferation, and to improve the maintenance of gut mucosal integrity [2
], with maintenance of trophism apparently being the key to the prevention of bacterial translocation [3
]. In addition, because the gut is the largest producer of humoral antibodies in the body, it is believed that improved immune responses to bacterial challenge in enterally, compared with parenterally, fed individuals may be important in preventing septic complications [2
Despite these advantages, enteral nutrition may not be tolerated by all patients and may cause fatal complications such as diarrhea, constipation, aspiration and bowel ischemia [4
]. Especially, nasoenteric feeding in critically ill patients is often complicated by diarrhea. When diarrhea develops in critically ill patients, it adversely affects their nutritional status, electrolyte imbalance and nursing care and places them at increased risk for infection in the recovery phase. This results in longer hospital stay, higher medical expenses and increased mortality. Attempts to control the diarrhea that accompanies tube feeding include either changing the enteral formula which is containing fiber.
We experienced two patients who manifested bowel ischemia associated with enteral nutrition. These two patients described here have several features in common. The nutritional formulas they were fed contained plenty of fiber, they received postoperative mechanical ventilatory support due to poor lung function, and they have no underling vascular disease which cause acute bowel ischemia. In both patients, however, inspissated muddy stools were seen in the resected bowel specimen. Several mechanisms have been proposed as contributing towards the development of enteral tube feeding associated diarrhea, which are discussed below.
First, the inspissated bowel contents may have put direct pressure on the mucosa of the bowel wall, leading to local impairment of mucosal blood flow with subsequent ischemic changes in the bowel. Both patients were supplied dietary fiber daily for several days. This commercially available formula (Jevity), contains soy polysaccharide, which has up to 94% insoluble dietary fiber with no soluble dietary fiber. Dietary fiber has become a standard component of enteral nutrition formulas to prevent and treat chronic constipation [5
]. Dietary fiber increases intestinal transit and stool bulk, stimulating voluntary defecation. The increase in stool bulk is thought to result from the residual, unfermented fiber, as well as from water held by gel formed by unfermented fibers. Direct pressure leading to bowel ischemia was suggested by our surgical findings. Pathologic examination also showed the evidence of mechanism of bowel ischemia. Pathologic finding showed no acute vessel occlusion, atherosclerosis of arterial vessels, or thrombosis. Mucosal thinning and diffuse flattening with hemorrhagic infarction are indicators of direct pressure from the lumen. Generally, in critically ill patient who have risks of bowel ischemia, most guideline recommend to supply soluble fiber-rich enteral formula.
Next, increased energy demand from enterocytes may also have contributed to enteral nutrition-associated bowel ischemia, in association with ischemic bowel change [6
], resulting in mismatches in the oxygen demand to supply ratio in the intestinal mucosa. Enteral nutrition leads to tropism of enterocytes [7
]. In the presence of luminal nutrients, splanchnic blood flow increases up to 200% that of baseline in response to the augmented demand of the intestinal mucosa, resulting in a regional blood-flow redistribution known as postprandial hyperemia [8
In conclusion, enteral nutrition has many benefits for critically ill patients and dietary fiber is important for stimulating the structural and functional trophism of the mucosa, preventing diarrhea by absorption of sodium and water [9
] and preventing bacterial translocation [10
]. However, the contents of enteral formula may lead to complications. An overabundance of insoluble dietary fiber in enteral nutrition may aggravate bowel ischemia. Stool bulkiness resulting from insoluble dietary fiber and low transit time may result in inspissated bowel contents. Especially, in patients who are hemodynamically unstable and hypoxic, bowel ischemia could also exacerbated. In these situations, it is important to reduce the proportion of insoluble dietary fiber. Physician in ICUs should be aware of enteral nutirtion associated non-occlusive bowel ischemia in patients with fever, tachycardia, leukocytosis, and septic shock of unknown origin.