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La utilización de la nutrición enteral (NE) en el paciente crítico hace necesario evaluar su eficacia e influencia en la consecución de los requerimientos pautados. La NE administrada a nivel gástrico tiene una tasa alta de complicaciones, particularmente aumento de residuo, que conlleva una infranutrición. La utilización del intestino delgado (yeyuno), puede conseguir un aumento del volumen administrado. Pero para ello hay tres aspectos que influyen directamente en su utilización: la vía de acceso intestinal, la capacidad motora y su capacidad absortiva y función de barrera. La elección de la vía de acceso al tubo digestivo debe realizarse tras valoración de la patología de base y el tiempo previsto de duración de la NE. Si es superior a 4-6 semanas se procederá a acceso definitivo a través de una técnica invasiva y ostomía (yeyunostomía radiológica, endoscópica o quirúrgica) y si es inferior a 4-6 semanas, técnica no invasiva o transnasal (nasoduodenal o nasoyeyunal) con endoscopia, fluoroscopia o ecografía. Se ha constatado que, mediante protocolización de los procedimientos y experiencia, la nutrición yeyunal puede conseguir un aumento de los requerimientos administrados al paciente crítico bajo ventilación mecánica respecto de la nutrición gástrica, aunque no son claros los beneficios en cuanto a la reducción de complicaciones infecciosas, estancia y mortalidad, por lo que su uso debe reservarse para aquellos casos en los que está documentado una clara intolerancia gástrica. Mediante técnica manométrica o con el test de absorción de acetaminofeno, se ha constatado que el 50% de los pacientes críticos con ventilación mecánica tienen, a nivel gástrico, hipomotilidad antral, disminución de los complejos motores migratorios y del vaciamiento gástrico, lo que dificulta considerablemente la nutrición. En condiciones normales, durante el ayuno existen unas contracciones motoras regulares o complejo motor migratorio interdigestivo cuyo patrón no es favorable a la absorción de nutrientes por ser altamente propulsivo, por lo que en la fase nutriente cambia al patrón postprandial, de actividad contráctil irregular y continua, sin frentes de actividad, mucho más adaptado a la absorción de nutrientes. En el paciente crítico se pierde este esquema propulsivo normal, desapareciendo con frecuencia el patrón postprandial y persistiendo el interdigestivo, lo que dificulta o impide la nutrición enteral. Son varios los factores que influyen en ese cambio, principalmente la patología de base, sepsis, TCE, ventilación mecánica, sedación y miorelajación. La utilización de agentes procinéticos, como la metoclopramida, puede, al menos en teoría, modificar la alteración de la motilidad y facilitar la correcta administración de los requerimientos pautados. Entre otras, el tracto gastrointestinal (TGI) desempeña una función de "barrera" entre los medios interno y externo que impide la entrada a sangre de bacterias, agentes antigénicos y tóxicos. Su fracaso se caracteriza por absorción disminuida de nutrientes, alteración de la respuesta inmunológica intestinal y aumento de la permeabilidad intestinal (PI). Entre las hipótesis que pretenden explicar la infección sistémica y el fracaso multiorgánico (FMO) figura precisamente el fallo en la integridad anatómica y funcional de la mucosa intestinal. Se ha constatado una alteración de dicha mucosa con aumento de la PI en patologías como quemados, politraumatismos, cirugía mayor, trasplante de células hemopoyéticas y sepsis, aunque no se ha establecido con claridad su relación con la traslocación bacteriana. Ante las evidencias que implican al TGI en el FMO, los métodos de monitorización dirigidos a corregir precozmente la hipopefusión esplácnica nos orientan sobre los mecanismos implicados en el aumento de la PI.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.

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. [ABSTRACT FROM AUTHOR]