Nutrition in the critically ill patient: part II. Parenteral nutrition.

OBJECTIVE To review the human nutrition in the critically ill patient in a three-part presentation. DATA SOURCES Articles and published peer-review abstracts and a review of studies reported and identified through a MEDLINE search of the English language literature on parenteral nutrition. SUMMARY OF REVIEW Intravenous nutrition plays an important supportive role in the management of the critically ill patient who has prolonged gastrointestinal failure. Energy substrates consist of concentrated glucose and lipid solutions, although the former requires central venous access for its administration. The nitrogen requirement is supplied as L-amino acids which usually consist of a solution containing the essential amino acids which are supplemented by a few of the non-essential amino acids. While, amino acid mixtures of glutamine dipeptides, ornithine alpha-ketoglutarate, asparagine, oxaloacetate, arginine, aspartate and glutamate have been used in a variety of conditions, prospective randomised controlled trials have not consistently demonstrated improved survival with their use in the critically ill patient. The water soluble vitamins and vitamin K should supplement intravenous nutrition with amounts at least to meet the recommended daily allowance. Additional supplementation of thiamine, folic acid and ascorbic acid are often administered in the critically ill patient. Apart from zinc, the body stores of the essential trace elements of zinc, copper, iodine, iron, manganese, cobalt, selenium, chromium, fluoride and molybdenum are usually adequate to meet the needs of patients requiring parenteral nutrition for less than 3 months. CONCLUSIONS In the critically ill patient with prolonged gastrointestinal failure, intravenous nutrition plays a supportive role in the management of a patient.