الفهرس 
Physiology of nutritionOnly 14 pages are availabe for public view
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Abstract
Nutritional support is essential for survival because it affects susceptibility to diseases and it is often neglected during treatment of the patients. After the resuscitation of the critically ill patients the nutritional status should be assessed and treated. Nutritional support has become a routine part of the care of the critically ill patients. The main goal of nutritional support is to prevent the development of malnutrition diseases. The effectiveness of nutritional support is affected by underlying metabolic disorders so that the design of a nutritional support regimen must therefore take into consideration underlying metabolic disorders.
Patients of the critical care illness are at high risk of malnutrition diseases due to the nature of their illness and their hypermetabolic state, their immune system is compromised, so they are at increased risk of infection and septicemia, delayed wounds healing which contribute to prolonged ICU stay, increased morbidity and mortality and higher treatment costs so that nutritional support in critical care illness from the onset of admission in ICU is imperative and very important.
Assessing the patients at risk of protein energy malnutrition by clinical history (e.g., nausea, vomiting, diarrhea, abdominal distension, previous surgery, and weight changes), dietary history (e.g., types and amounts of food taken, dysphagia), and physical examination (e.g., weight height ratio, body mass index, general appearance). The tests which can be used to establish the severity of protein energy malnutrition and the response to nutritional support are (anthropometric e.g., skin fold thickness, biochemical tests e.g., albumin, transferrin and pre-albumin, and immunological e.g., lymphocyte count).
The critical ill patients need more energy up to 30% because the metabolism is affected by the changes in the levels of catecholamines and cortisol hormones in the blood, the blood sugar becomes deranged as patients develop resistance to insulin hormone and there are major fluid and electrolyte losses from (diarrhea, vomiting, excessive sweating or nasogastric losses and surgical drains). In critical illness the fluid shifts caused by leaky membranes or fluid moving into the third space, create difficulties in assessing fluid balance.
Macronutrients (proteins, lipids and carbohydrates) are required in large amounts to provide the body by energy requirements while micronutrients (vitamins and minerals) are required in very small amounts to maintain health. Protein provides the body with 5.3 kcal/g and the requirements around 1.5 g/kg/day (range 1.2 to 2.0 g/kg/day for ICU patients) or we use 2g/kg/day if severely catabolic e.g., severe sepsis/burns/trauma. Lipid provides the body with 9.3 kcal/g. Calories from lipid should be limited to 40% of total calories. The remaining energy requirements should be given as carbohydrate which provides the body with 3.75 kcal/g. Vitamins are organic compounds used as cofactors for enzymes involved in metabolic pathways. Minerals act as an ions and cofactors for enzymes or as structurally integral parts of enzymes and are often involved in electron transfer.
Nutrition in critical ill patients either enteral nutrition or parenteral nutrition. Enteral nutrition means using the gastrointestinal tract for the delivery of nutrients. The most common route of enteral tube feeding is nasogastric rout. The most common side effects of enteral tube feeding are aspiration of food and vomiting in these cases the rate or methods of administration need to be reviewed. Some patients fail to tolerate large volumes at one time, in these cases the pump rate should be slowed and a higher energy feed should be used and increase the period of rest between each meal to allow gastric emptying.
Parenteral nutrition means using the veins for the delivery of nutrients. Parenteral nutrition should only be administered if there is contraindications to enteral feeding e.g., diffuse peritonitis, intestinal obstruction, intractable vomiting, paralytic ileus, and severe diarrhea. Parenteral nutrition always associated with biliary stasis, hyperglycemia and higher infection rates in comparison with enteral feeding.
Immunonutrition is a new concept in critical care feeding to which there is a growing body of evidence reporting benefits. Immunonutrition contain amino acids arginine and glutamine, omega-3 fatty acids, nucleotides. Arginine is an amino acid shown to improve immune response to bacteria, viruses and tumor cells, promote wound healing and increase protein turnover. Omega-3 fats enhance immune function by boosting neutrophil activity and reduce inflammations. Nucleotides are essential for maintaining cellular integrity and enhancing production of repair cells. Glutamine is non essential amino acid because it is more abundant in the body but it becomes essential in critical ill patients.