Adequate nutrition should be viewed as important part of the healing process for patients seeking treatment in hospitals. However, it is not uncommon for nutritional status of many patients who have just undergone surgery to decline because the metabolic response to trauma, surgery and in some cases infection resulting in increased energy demands for such major stress are not adequately compensated for. The rate of proteolysis and lipolysis is greatly accelerated by the release of glucocorticoids and cytokines such as interleukin-6 and lymphokines resulting in the depletion of glucose and fatty acids stores to meet the energy demand. Protein stores are not spared as well, because the skeletal muscle relies on free fatty acids and its own catabolised protein as its primary source of energy.
Postoperative patients may require 35-45 kcal/kg per day and 2 -3gkg-1 of protein per day while patients with severe burns may require even more. When a patient is not able to ingest enough food it may be appropriate to supplement the diet with high calorie- high protein preparations to meet the short term caloric and protein needs. However, some patients may be unable to ingest solid food or to digest complex mixtures of food adequately, elemental diets which consist of glucose, dextrins, fats, amino acids, vitamins can be administered as substitute via a nasogastric tube.
It is noteworthy that when a patient is unable to absorb food normally, parenteral nutrition (PN) is necessary. The least invasive method is to use a peripheral, slow-flow vein IV infusion. The main limitation of this method is hypertonicity. However, a solution of 5% glucose and 4.25% of amino acid can be used safely. This solution will provide enough protein to maintain positive nitrogen balance, but will rarely provide enough calories for long term severely catabolic patients.
The most aggressive nutritional therapy is total parenteral nutrition. Usually an indwelling catheter is inserted into a large fast flow vessel such as the superior vena cava, so that the very hypertonic infusion fluid can be diluted rapidly. This allows solutions of up to 60% glucose and 4.25% amino acids with lipids to be used, providing sufficient protein, essential fatty acids and most of the calories for long term maintenance.
Any of the method mentioned can be used to prevent or minimise the negative nitrogen balance associated with surgery and trauma. The choice of the method depends on the patient’s condition. As a general rule, it is preferable to use the least invasive technique.
Thomas M Devlin (2006). Principles of nutrition 1: Macronutrients. Clinical correlation 27.3. Textbook of Biochemistry.