artificial feeding Patients require artificial feeding if they are unable to take adequate food by mouth, or if the small intestine is unable to absorb nutrients from their food. For example, coma or paralysis of the throat muscles can prevent normal swallowing; diseased small intestine may have to be removed by surgical operation which leaves insufficient area to absorb enough nutrients for the patient to survive.

Patients may also require artificial feeding when they have developed major infection or received severe injury such as occurs after a large area of skin is burned. In these situations, patients have a much larger requirement for nutrients and artificial supplements may be required. The aim of artificial feeding is to supply all the nutrients which are essential for the body to survive and, especially in young patients, to allow normal development.

Artificial feeding can be achieved by two different methods. The nutrition can be delivered into the gut whence it can be normally absorbed (enteral) or administered directly into the blood stream (parenteral).

Enteral feeding

is used when a patient has an adequately functioning bowel, but cannot eat sufficient nutrients — such as a patient receiving artificial ventilation in an intensive care unit who is too sedated to be able to eat and drink normally. Enteral feeding can be achieved by passing a fine-bore tube through the patient's nose into the stomach or upper part of the small bowel. If prolonged enteral feeding is anticipated, this nasogastric tube is replaced by a gastrostomy tube, which passes through a small opening made surgically through the skin of the abdomen into the stomach. Where the patient's upper digestive system has some disease process or has undergone surgery, this can be bypassed by placing a feeding enterostomy tube in the lower part of the small bowel.

The major benefit of using enteral feeding is that nutrition is delivered into the small bowel and the normal route is used for nutrient absorption. In addition, enteral feeding may improve the ability of the gut to resist infection, which is extremely important in patients who may already have decreased resistance. This form of artificial feeding minimizes problems of access to a patient's veins, and there is far less chance of infection than parenteral with feeding.

Parenteral feeding

This is used in those circumstances when it is not possible to deliver artificial feeding into the gut. Patients who have disease of the bowel or who have undergone major bowel surgery may then require parenteral nutrition. With this type of artificial feeding, the nutrients are usually delivered directly into the bloodstream. A small tube (cannula) is placed into a large vein in the neck or above the collar bone. The insertion of this cannula is a very specialized technique and in some cases may require a surgical operation under general anaesthesia.

This central venous cannulation may be associated with several complications, such as blockage of the cannula which then has to be replaced, or infection which may require that the cannula is removed until the infection has been treated successfully. The risk of such complications increases with time, and access to a suitable vein can become increasingly limited as the possible sites for placing the cannula are used. This is especially so in children. Because of these problems the parenteral route for administration of nutrition is reserved usually for patients with high caloric requirements and a non-functioning gut. It may also be used in children who cannot tolerate enteral feeding.

Artificial feeding can improve wound healing and may lead to faster and better recovery after major surgery or other form of severe tissue damage. Even when some food and drink is taken by mouth, it may not be adequate to provide the extra nutrition required for repair.

Gavin Kenny

See also alimentary system; coma; eating; life support.