Assessment of knowledge concerning the clinical use of protein hydrolysates and pure amino acid mixtures

Abstract

Available evidence indicates that nitrogen equilibrium can be maintained and the protein requirements of normal animals, including man, apparently met by intravenous infusion of properly prepared hydrolysates of biologically efficient proteins. But there is no evidence that the intravenous route is superior from the nutritive standpoint to the normal method of feeding. Indeed, if hydrolysates are injected too quickly, nausea and perhaps vomiting may lead to less efficient use of the amino acids and peptides. It is seldom possible to give routinely more than the equivalent of 75 Gm. protein and 300 to 400 Gm. glucose by the intravenous route. There does not appear to be any solid evidence for the use of hydrolysates orally or by tube into the alimentary canal. While there is abundant evidence of the life-saving benefits which immediately accrue from the use of whole blood or plasma, these proteins also serve as a source of nutrition. There is some doubt whether the intravenous use of intact proteins will permit certain effects which are bound up with intermediary metabolic changes which follow the ingestion of protein in the food or the infusion of amino acid mixtures by vein. Mixtures of pure amino acids lack certain peptide fragments which may be necessary for growth and the full maintenance of nutrition. To save body protein it may be wise to include all the amino acids rather than to rely on the essential amino acids plus glycine. The rationale for employing amino acid mixtures parenterally in place of, or along with, intact blood proteins rests more on the necessity to sustain liver function and to maintain a more vigorous nitrogen turnover than to the need for building up a store of nitrogen. This line of treatment may be worthy of further exploration. Because of the difficulty of infusing sufficient protein and energy in the infusion fluid, it is generally agreed that it is not possible to make good the requirements of the protein-depleted organism entirely by intravenous injection. It is not wise to give fluid containing more than 5 per cent hydrolysate and 5 per cent glucose. Mixtures of pure amino acids may be given at 8 per cent strength. Even these levels necessitate some four hours to provide 2,000 ml. The whole procedure causes discomfort if not actually distress to the patient and also prevents rest. The calory requirements are but inadequately met by these procedures although it is held that for short periods of time the glucose intake can be safely limited to 100 Gm., the rest of the energy needs being met from the adipose tissue and the 100 Gm. of hydrolysate preventing further protein loss. More corroborative evidence is required on this fundamental issue. It may be wise to restrict the use of intravenous hydrolysates and mixtures of pure amino acids to postoperative patients with previous protein depletion which has to be corrected preoperatively and sustained postoperatively, and secondly to those in whom evidence of a postoperative complication has already appeared. Amino acid mixtures including hydrolysates are of value in treating conditions in which it is absolutely necessary to have complete rest of the alimentary canal, for example, in acute mercury poisoning. Indications for parenteral feeding are inability to ingest, digest or absorb adequate quantities of food over such a period of time as to jeopardize the chance of an uneventful convalescence and which may even prejudice the chance of survival.