Full circle in parenteral nutrition

Abstract

The first tentative steps in the development of intravenous nutrition were made during the First World War. Iso-osmotic glucose solution was the only energy substrate available and the number of calories that could be administered was restricted to the volume that could be tolerated since peripheral veins were the only routes of administration. Although some authors, with the help of diuretics, could administer some 400-500g of glucose (1600-2000 kcal/day) with this technique it was clearly impractical for routine clinical purposes. By the late 1930s protein hydrolysates were under extensive study and it was not long after that the first fat emulsions were being proposed for intravenous use. A major turning point in the development of effective intravenous nutrition came about following the description by Aubaniac, a French surgeon, of the technique of subclavian cannulation. He perfected this method of vascular access during the Second World War and his technique was subsequently adopted by Dudrick and colleagues. These workers found that they could infuse combinations of protein hydrolysates and hypertonic dextrose solution without risk of thrombophlebitis into the subclavian vein. Using this technique they achieved long-term nitrogen balance and actual growth in puppies and these experiments marked the origin of parenteral nutrition as we know it today (1). In these early days hypertonic glucose solutions were the preferred energy source and the osmolarity of these solutions, together with that of the amino acid sources, precluded the use of peripheral veins. The ability to perform central venous catheterisation safely became, therefore, an essential prerequisite of successful total parenteral nutrition (TPN). This, in itself, restricted the use of parenteral nutrition in many hospitals where such expertise was not available. Intravenous nutrition is now an established part of the care of patients in whom enteral absorption of nutrients is insufficient to meet caloric needs. Advances in pharmaceutical technology, improvements in delivery equipment, and increased knowledge of metabolism and nutrition, have made it possible to provide all patients regardless of disease state with adequate intravenous feeding sufficient to meet all their needs. There is, however, a general awareness amongst the medical community that TPN is itself associated with some morbidity and on rare occasions mortality (2). Metabolic complications, common in the past, are now infrequent with careful patient surveillance, and toxic reactions to nutrient solutions have been virtually eliminated. Most complications these days are related to the catheter or the venepuncture. These may be mechanical, thrombotic or septic in nature and will occur in between 4 and 10% of all patients receiving TPN through a central venous line (2). This significant morbidity has, understandably, caused many clinicians to question the necessity for TPN, with the inevitable consequence that certain patients are probably denied appropriate nutritional support if local expertise in techniques of central venous cannulation are not available. This restraint in the use of TPN is obviated by peripheral administration of all nutrient solutions. It is only as a consequence of certain research developments in recent years that TPN via a peripheral route (PPN) has become a viable alternative to central venous administration. Arguably, the most significant of these research developments was the development by Wretlind and his colleagues of a safe non-toxic intravenous fat emulsion (3). Fat emulsions being isotonic may be infused through a peripheral line and their high energy density are helpful for reducing total fluid volumes. During the early years of TPN calorie intakes were frequently based on the incorrect assumption that energy and protein requirements were directly related on the basis of a 2OO:l ratio. This