الفهرس 
Pathophysiology of Acute Lung Injury and Acute Respiratory Distress SyndromeOnly 14 pages are availabe for public view
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Abstract
Acute respiratory distress syndrome (ARDS) is a type of respiratory failure characterized by the acute onset of bilateral alveolar infiltrates and hypoxemia.
The Berlin Definition of ARDS (published in 2012) has replaced the American-European Consensus Conference‘s definition of ARDS (published in 1994).
Healthy lungs regulate the movement of fluid to maintain a small amount of interstitial fluid and dry alveoli. In patients with ARDS, this regulation is interrupted by lung injury, causing excess fluid in both the interstitium and alveoli. Consequences include impaired gas exchange, decreased compliance, and increased pulmonary arterial pressure.
Patients with ARDS tend to progress through three relatively discrete pathologic stages: the exudative stage, proliferative stage, and fibrotic stage.
More and more possible causes of ARDS have been identified and other potential causes continue to emerge as adverse pulmonary reactions to new therapies are observed. However, only a few common causes account for most cases of ARDS.
Most current therapies for ARDS are supportive, aimed at improving gas exchange and preventing complications while the underlying condition that precipitated the ARDS is addressed.
Nutrition support refers to the enteral or parenteral provision of calories, protein, electrolytes, vitamins, minerals, and fluids. Enteral nutrition is the preferred method for feeding critically ill patients with functioning gastrointestinal tract. Enteral nutrition improves several clinical outcomes like infectious complications and ICU or hospital length of stay. Indeed, enteral nutrition seems to play a role in the modulation of the immune system of critically ill patients.
Several specific substrates with immunological effects have been added, alone or in combination, to standard diets trying to modify the immune response of the
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patients. The number of these key nutrients, also called immunonutrients, is now increasing but arginine, glutamine, nucleotides and omega-3 polyunsaturated fatty acids seems to play a primordial role in the regulation of immunological and inflammatory responses in critically ill patients.
ARDS are associated with disease states characterized by a hypermetabolic response. Clinical states such as sepsis, pancreatitis, aspiration pneumonia, and severe trauma are associated with marked hypermetabolism secondary to the inflammatory process. Providing nutritional support to these patients early in their disease course is essential in order to minimize the loss of lean body mass and to provide adequate energy for metabolic support.
Enteral nutrition is the preferred nutritional support method due to its reduced septic risk, lower cost, and role in maintaining the gastrointestinal barrier function.
Energy requirements among ARDS patients vary considerably based on the underlying clinical state. Indirect calorimetry (IC) is the most accurate method for measuring energy expenditure in hospitalized patients. Despite its superiority, IC use in ARDS has its limitations.
Patients with ARDS have increased protein requirements because of the rapid protein turnover known to occur in hypermetabolic states. Nutritional-support regimens that provide a balance of carbohydrate and fat as nonprotein energy should be adequate for optimal substrate utilization.
An enteral product designed specifically for the ARDS patient is available. This product is a reduced-carbohydrate formula supplemented with eicosapentanoic acid and g-linolenic acid. It is known in ARDS that inflammatory mediators alter the metabolic pathways of these fatty acids, resulting in reduced levels of them.
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Selecting the appropriate nutritional strategy for critically ill and injured patients has undergone a paradigm shift. Previously, the decision was regarded as supportive, simply a measure to provide for the individual patient‘s energy and nutritional requirements. But now, the decision is increasingly complex: the type of formula is expected to alter the body‘s metabolic response to injury, to balance oxidative processes, and to help regulate the immune system, which may be deranged because of the underlying disease.