If the body is unable to digest or absorb nutrients by normal physiological processes, parenteral feeding bypasses these by delivering predigested nutrients directly to the bloodstream by way of central or peripheral venous access.  Parenteral nutrition generally provides adequate amounts of glucose, amino acids, fat, electrolytes, vitamins, and trace elements. The required optimal amount of each nutrient  varies with different clinical scenarios. The terms total parenteral nutrition, hyperalimentation, parenteral nutrition support, and parenteral feeding have been used interchangeably to describe this medical intervention.

Traditionally, TPN has been widely used in oncology practice and information from this source is worth noting. During chemotherapy and radiotherapy nutrition is often impaired. In one study evaluating the use of TPN in cancer patients, no statistically significant benefit could be demonstrated in survival, treatment tolerance, treatment toxicity or tumour response.

In 1989, the American College of Physicians published a position paper on TPN in patients receiving chemotherapy. They concluded that parenteral nutrition support was associated with net harm, and no conditions could be defined in which such treatment could benefit patients. The major iatrogenic complications were pneumothorax, subclavian and axillary vein thrombosis and catheter related scepticaemia.

Research suggests that parenteral nutritional support was associated with net harm. Routine use for patients undergoing chemotherapy should be strongly discouraged. In deciding to use such therapy, doctors should take into account this increased risk. So far, subgroups where parenteral nutritional support have not been identified.