[Enteral access and intestinal function assessment in the critically ill patient].

The use of enteral nutrition (EN) in the critically-ill patient makes necessary to evaluate its effectiveness and impact on achieving the target requirements. Gastrically administered EN has a high complication rate, especially increased residue that leads to hyponutrition. The use of the small bowel (jejunum) may achieve greater administered volume, although there are three aspects that directly influence on its use: intestinal access route, motility and absorptive capability, and barrier function. The selection of the access route to the digestive tube has to be done after evaluating the underlying disease and predicted duration of EN. If it is greater than 4-6 weeks a definitive access will be performed through an invasive technique of ostomy (radiologic, endoscopic or surgical jejunostomy) and if it is shorter than 4-6 weeks, an endoscopic, fluoroscopic or ultrasonographic non-invasive or transnasal technique (naso-duodenal, or nasojejunal) will be used. By protocoling procedures and experiences, it has been shown that jejunal nutrition may achieve an increase in the amount of requirements administerd to critically-ill patients with mechanical ventilation as compared to gastric feeding, although the benefits with regards to reducing the number of infectious complications, hospital stay and mortality are not so clear-cut, so that it should be left to those cases in which gastric feeding has been clearly documented. By using the manometrich technique or the acetaminophen absorption tests it has been shown that 50% of critically-ill patients with mechanical ventilation have gastric antral hypomotility with decreased migratory motor complexes and gastric voiding, which considerably hampers nutrition. Under normal circumstances, during fasting, there are regular motor contractions, or an inter-digestive migratory motor complex which pattern prevents nutrient absorption because of being highly propulsive, so that during the nutrient phase, this pattern changes into the postprandial pattern with an irregular and continuous contraction activity, with no activity centers, which is much more adapted to nutrient absorption. In critically-ill patients, this normal propulsive pattern is lost, the postprandial pattern is frequently lost, and the inter-digestive pattern remains, which prevents enteral feeding. There are several factors that have an impact on this change, mainly the underlying disease, sepsis, head trauma, mechanical ventilation, sedation, and muscle relaxation. The use of pro-kinetic agents such as metoclopramide may, at least theoretically, modify motility impainment and facilitate the correct administration of prescribed requirements. Among other functions, the gastrointestinal tract (GIT) has a barrier function between inner and outer media, which prevents bacteria, antigenic agents, and toxicants from entering the blood. Its failure is characterized by decreased nutrient absorption, impaired intestinal immunological response and increased intestinal permeability (IP). Among the hypothesis trying to explain systemic infection and multiorgan failure (MOF), there is precisely anatomical and functional integrity of the intestinal mucosa. Mucosal impairment with increased IP has been shown in burn patients, polytrauma, major surgery, hematopoietic cell transplantation, and sepsis, although its relationship with bacterial translocation has not clearly been established. Before the evidences that link the GIT with MOF, the monitoring methods aimed at early correction of splaenic hypoperfusion focus on the mechanisms implicated in increased IP.