Feeding the hypotensive patient: does enteral feeding precipitate or protect against ischemic bowel?

Although the enteral route of enteral feeding is the preferred method of nutrition support for critically ill patients, this important therapeutic strategy is not without risk. In human subjects, the digestion and absorption of nutrients induce typical hemodynamic changes, consisting of an increase in mesenteric blood flow at the expense of reduced systemic blood pressure. On rare occasion when providing aggressive enteral nutrition to critically ill patients, common symptoms of gastrointestinal intolerance may progress to a syndrome of abdominal distention, hypotension, and shock, with the development of small bowel ischemia or necrosis. Although the incidence of small bowel ischemia secondary to enteral feeding is low, the overall clinical outcome is still poor and carries a high mortality rate. Enteral feeding is well tolerated and is probably beneficial in most critically ill patients before and after a period of hypotension. Although enteral nutrition may be used with caution during the period of hypotension, evidence of poor gastrointestinal function (increased nasogastric tube output, unexplained abdominal pain, and abdominal distention), or development of dilated loops of bowel or intramural gas (pneumatosis intestinalis) on radiographic studies should be interpreted as potential indicators of gut ischemia. With progress in our understanding of the pathophysiology, diagnosis, and prevention of ischemic injury to the intestinal mucosa, the strategy of aggressive enteral feeding for critically ill patients may result in a reduction in this major complication and enhanced functional recovery from severe illness.