title: The role of macronutrients in gastrointestinal blood flow.
abstract: OBJECTIVE
  The presence of luminal nutrients after a meal increases gastrointestinal blood flow in a phenomenon called postprandial hyperemia. In many conditions related to splanchnic hypoperfusion, enteral nutrition may play a role in counterbalancing the installed splanchnic low-flow state by producing intestinal hyperemia. However, when the gut is hypoperfused there is a chance of enteral nutrition producing a mismatch of the oxygen demand: supply ratio with subsequence gut ischemia. This article aims to review the effects of macronutrients on gastrointestinal blood flow in both health and critical conditions, especially those related to hepatosplanchnic hypoperfusion.
  
  
  RESULTS
  Splanchnic blood flow is related not only to the route (intravenous or enteral) and timing of nutritional support (during the course of the insult) but also to the composition of the formula. Critically ill patients with gut hypoperfusion may tolerate enteral nutrition, but this effect may be restricted to the early post-injury phase. During ischaemia reperfusion injury, immune nutrients may promote different outcomes: glutamine may protect whereas arginine may deteriorate the mucosal barrier and enhance permeability.
  
  
  CONCLUSIONS
  Understanding the relationship between macronutrients and gastrointestinal blood flow is a major challenge. Ongoing research in nutritional support in hypoperfused, catecholamine-dependent patients will open the door to optimize the recovery of patients in critical care.
authors.affiliation: Department of Surgery, Federal University of Mato Grosso, Cuiaba, Mato Grosso, Brazil. aguilar@terra.com.br
authors.forename: José Eduardo
authors.initials: JE
authors.lastname: de Aguilar-Nascimento
mesh_terms: D016638:Critical Illness / Q000628:therapy*; D004040:Dietary Carbohydrates / Q000008:administration & dosage / Q000378:metabolism; D004041:Dietary Fats / Q000008:administration & dosage / Q000378:metabolism; D004044:Dietary Proteins / Q000008:administration & dosage / Q000378:metabolism; D041981:Gastrointestinal Tract / Q000098:blood supply* / Q000502:physiology*; D006801:Humans; D007413:Intestinal Mucosa / Q000098:blood supply; D018529:Nutritional Support; D013152:Splanchnic Circulation / Q000187:drug effects*
chemical_list: D004040:Dietary Carbohydrates; D004041:Dietary Fats; D004044:Dietary Proteins