In severely ill patients, the metabolic responses to tissue damage may be sufficient to cause a reduction of muscle mass and of plasma proteins. This state of CATABOLISM may also impair the immune response to infection and delay the healing of wounds. It is probable that as many as one-half of patients who have had a major operation a week previously show evidence of protein malnutrition. This can be detected clinically by a loss of weight and a reduction in the skinfold thickness and arm circumference. Biochemically the serum ALBUMIN concentration falls, as does the LYMPHOCYTE count. The protein reserves of the body fall even more dramatically when there are SEPSIS, burns, acute PANCREATITIS or renal failure.

The purpose of enteral feeding is to give a liquid, low-residue food through a nasogastric or orogastric feeding tube. It has the advantage over parenteral nutrition that the septic complications of insertion of CATHETERS into veins are avoided. Enteral feeding may either take the form of intermittent feeding through a large-bore nasogastric tube, or of continuous gravity-feeding through a fine-bore tube. When long-term enteral feeding is envisaged, for example in patients with neurological conditions affecting the ability to swallow, a semi-permanent STOMA may be fashioned between the stomach and the abdominal muscle and skin (gastrostomy).

A number of proprietary enteral foods are available. Some contain whole protein as the nitrogen source; others – and these are called elemental diets – contain free amino acids. DIARRHOEA is the most common problem with enteral feeding and it tends to occur when the feeding is introduced too rapidly or with too strong a preparation.