OVERVIEW
Intestinal dysfunction is defined as impairment of intestinal digestion, absorption and barrier function due to various diseases, resulting in malnutrition, intestinal mucosal damage and enterogenic infections. It has long been recognized that the intestine has only digestive and absorptive functions, but the presence of a large number of pathogenic bacteria, toxins, and xenoantigens in the intestine under normal conditions does not cause disease, suggesting that the intestinal tract serves as a barrier to the aforementioned substances. Studies have proved that the intestine plays an important role in the development of systemic inflammatory response syndrome (SIRS), sepsis, and multiple organ dysfunction syndrome (MODS), and therefore it is believed that the intestine is not only the target organ of MODS, but also the initiator of MODS. In recent years, intestinal barrier function has become an important indicator for judging the prognosis of critically ill patients, and intestinal barrier dysfunction, intestinal bacterial and endotoxin translocation is an important factor leading to SIRS, MODS, and even multiple organ failure (MOF).
Etiology
Intestinal mucosal barrier damage is mainly caused by the following factors.
1. Severe trauma, burns, infection, shock, etc. lead to insufficient effective blood circulation in the intestinal tract, ischemia and hypoxia activate xanthine oxidase, producing excessive oxygen radicals and damaging the intestinal mucosa.
2. Various primitive blows reduce the ability of intestinal uptake and utilization of oxygen, reduce the energy supply of intestinal epithelial cells, and affect the repair of intestinal mucosa. In addition, because glutamine (GLn) as the main energy source of intestinal epithelial cells, can protect the epithelial cells against endotoxin/oxidant-related damage, intestinal uptake, utilization and the activity of the main hydrolytic enzymes of GLn after trauma are significantly reduced, also affecting the intestinal mucosal repair.
3. Bacterial overgrowth in the intestinal lumen, increase in the number of bacteria adhering to the intestinal wall, increase in the chance of colonization, produce a large number of metabolites and toxins, and damage the structure of the intestinal mucosa.
4. Activation of intestinal antigen-presenting cells, release of platelet-activating factor (PAF), tumor necrosis factor (TNF) and other cytokines, causing damage to the intestinal mucosal barrier function.
Symptoms
Intestinal dysfunction is mainly manifested in the following aspects.
1. Damaged intestinal mucosal barrier
When the intestinal mucosal barrier of the body is damaged and bacteria/endotoxin are displaced, intestinal bacteremia and endotoxemia can be formed, which in turn induces MODS.The release of a large number of cytokines and inflammatory mediators accompanied by MODS further aggravates the damage of intestinal mucosa. Various cytokines and inflammatory mediators involved in this process interact with each other, expanding the inflammatory response and forming a vicious circle.
2. Intestinal microecological disorders
Once there is a change in the number and/or localization of the flora in the intestine, for example, a large number of Staphylococcus, Escherichia coli, Proteus, Candida albicans, etc. can inhibit the normal reproduction of anaerobic bacteria such as Bifidobacterium, Lactobacillus, etc., thus causing bacterial dysbiosis. Bacteria/endotoxin migrate in large quantities, and enterogenic bacteremia and endotoxemia can be formed, infecting tissues and organs.
3. Intestinal dyskinesia
Under normal circumstances, intestinal peristalsis is an important mechanism of intestinal non-immune defense, which participates in the digestion, absorption and excretion of food, and is also the “scavenger” of the intestinal lumen environment, which prevents the accumulation of harmful substances in the intestines, including endotoxin, and restricts bacterial growth. Intestinal peristalsis is too slow, too weak or intestinal obstruction can cause intestinal bacterial overgrowth and lead to “small intestinal bacterial contamination syndrome”.
4. Impaired immune function
The main manifestations are a decrease in the content of secretory immunoglobulin A (sIgA), a decrease in the number of plasma cells synthesizing sIgA and a decrease in the number of gram-negative bacteria encapsulated by sIgA, a decrease in intestinal resistance, and an increase in bacterial/endotoxin translocation in the intestinal tract.
Tests
1. Intestinal mucosal permeability test
There are many methods of detection, various mono- and polysaccharide absorption and excretion tests and nuclear tracer methods.
2. Indirect measurement
Bacterial counts are measured by aspiration of the upper jejunal contents, and various hydrogen exhalation tests are used to detect the presence of bacterial overgrowth in the intestinal tract, thus indirectly evaluating intestinal function.
The accuracy of the above tests is controversial and difficult to apply in critically ill patients.
Diagnosis
There is no consensus on the diagnostic criteria for intestinal dysfunction. Some clinicians suggest that gastrointestinal failure should be diagnosed when the amount of gastrointestinal bleeding reaches more than 2,000 ml, but there is still no standardized intestinal dysfunction scoring and grading criteria.
Treatment
In addition to actively controlling the primary disease and symptomatic supportive treatment for important organs, the treatment of intestinal mainly includes transgastrointestinal nutritional therapy, preventing the destruction of intestinal mucosal barrier, applying microorganisms to consolidate the intestinal biobarrier, restoring the ecological balance of intestinal flora, selective intestinal decontamination as well as the selection of traditional Chinese medicine treatment, and so on.