New developments in lipid emulsions for parenteral nutrition

More than one thousand publications have demonstrated the safety and efficacy of today's lipid emulsions including long chain fatty acids under experimental and clinical conditions. This has resulted in a general acceptance of a dual energy system comprising both carbohydrates and lipids as non-protein calories in total parenteral nutrition. Non-carnitine-dependent fatty acid has been suggested as a superior energy source in clinical situations where carnitine may be in the subnormal range. A medium chain triglyceride (MCT) emulsion would provide an energy source with a more readily oxidizable substrate. The tolerance of MCT is less than that of long chain triglyceride (LCT), whereby only physical mixtures of these emulsions will be used in humans. A structured lipid (SL) is a triglyceride which includes both medium and long chained fatty acids within the same triglyceride. Emulsions including SL have demonstrated a decreased protein energy expenditure and increased serum albumin in burned animal. The SL has also been superior to LCT emulsions in stimulating muscle protein synthesis and maintaining body weight in hepatectomized animals. These positive effects on protein kinetics have been concomitant with a lower RES involvement during septicemia in burned guinea pigs. Emulsions including fatty acids with odd-number carbons give a possibility to provide a fat emulsion which also could contribute positively to the glucose homeostasis. The omega-3 family of fatty acids has demonstrated a potential pharmacologic effect with regard to their ability to decrease blood viscosity and improve survival rate in endotoxin shock in an experimental model. These observations have been ascribed to changes in thromboxin A2 levels.(ABSTRACT TRUNCATED AT 250 WORDS)

The metabolic response to glycerol during parenteral nutrition

The use of various nonprotein energy sources in parenteral nutrition regimens has been discussed for many years. Besides glucose, glycerol, xylitol, fructose and sorbitol are currently being used as water-soluble parenteral fuels. Despite the increasing frequency with which these glucose substitutes are being used, little information is available regarding the differences they evoke in host responses. All experimental evidence to date has shown glycerol to be equally effective in sparing body nitrogen as glucose when supplied in hypocaloric amounts. Results from studies in injured animals suggest that exogenously administered glycerol is a more potent inhibitor of fatty acid oxidation than glucose. Although results from human volunteers have been variable, glycerol administration after injury appears to markedly reduce fatty acid oxidation and ketogenesis, as well as increase hepatic glycogen. Glycerol toxicity appears to result only from its excessive administration, or when administered intraperitoneally or subcutaneously. Intravenous administration of hypocaloric quantities of glycerol alone or as a component of total parenteral nutrition is safe and effective.

Nutrient requirements in various clinical conditions

We now have a fairly good knowledge of the number of essential nutrients required in man. However, the studies are limited on the exact basic, minimal and optimal requirements of these nutrients in various conditions. Many more investigations are necessary in this field of clinical nutrition. We also need more information on the various biological and clinical parameters to be used in such studies. However, the present recommendations of the nutrient intakes in various clinical situations seem to be sufficient to maintain or obtain a good nutritional status in many clinical conditions and to prevent nutrient deficiency symptoms. Most of these recommendations are generous in relation to the basic requirements. The achievements in this field make us currently able to nourish our patients properly either by well-balanced ordinary hospital food or by tube feeding or parenteral nutrition.

Standards for nutritional adequacy of the diet: European and WHO/FAO viewpoints

The dietary recommendations of FAO/WHO and of the various European nations differ in several ways. There are two types of dietary recommendations or standards. The first is related to the recommended daily intake of nutrient and the second refers to the nutrient content of the diet expressed either as percentage of total energy (energy % or cal %) derived from protein, fat, and carbohydrate or as the amounts of nutrients in relation to units of energy, the so-called nutrient concentration or nutrient density (weight per 1000 kcal, per 1 MJ or per 10 MJ). The numbers of recommended nutrients vary between eight and 28. The recommendations are given for individuals of different age, sex, and physiological status. The highest number of subgrouping is 41 and the lowest 11. The ranges of recommended values are sometimes very wide, but all seem acceptable from the nutritional point of view. There are many good reasons for this situation such as cultural background, food tradition, food production, and availability.

Development of fat emulsions

The studies on the possibility of preparing IV fat emulsions began in the 1920's; since then, a very large number of emulsions with various fats and emulsifiers have been investigated. However, none of the early fat emulsions could be used safely in man. By the trial and error technique, a method was finally found to prepare soybean oil and egg yolk phospholipids to make a fat emulsion that had a low incidence of adverse reactions. A newly devised biological test system based on nutritional concepts was of crucial importance. It meant that any energy supplying nutrient should be tested in animals in relation to the energy requirement of the species used and not identical to the human dose/kg body weight as in the "classical" toxicity and tolerance tests. With the development of well-tolerated IV fat emulsions it has been possible to devise a TPN regimen that is adequate from a nutritional point of view as well as an adequate alternative to the ordinary oral food. This regimen, which can be administered by the peripheral route, means that the original aims for developing IV fat emulsions were finally achieved.

Parenteral nutrition

Parenteral nutrition therapy was born 35 to 40 years ago when the first steps were taken to perform a protein nutrition by the intravenous supply of amino acids in man. Since that time, many efforts have been made to supply adequate amounts of energy intravenously. These efforts have resulted in the two available systems for parenteral nutrition: the lipid-carbohydrate system and the glucose system. The lipid-carbohydrate system, which corresponds to the nutrient content of normal food, may be given either in a peripheral vein or through a central vein catheter. The glucose system is administered through a central venous catheter. Many problems concerning the parenteral nutrition need to be solved and further elucidated. However, our present knowledge and technique in this field are far advanced over earlier methods. Now all patients who cannot take food in adequate amounts orally or enterally may be kept in good nutritional status by parenteral nutrition. In this way it is possible to prevent starvation and its complications in these patients.

[General aspects of intravenous feeding of cancer patients]

In order to obtain or maintain a good nutritional status in cancer patients, it is often necessary to perform intravenous nutrition. In summary, several studies have indicated that intravenous nutrition may be beneficial in association with surgery, radiation, or chemotherapy in patients with cancer. More controlled studies, however, are required. There is no indication at the present time of any adverse effects of this method of treatment in relation to tumor growth. The general nutritional improvement in patients on intravenous nutrition increases the immunocompetence, resistance to radiation and cytostatics as well as the mood and quality of life of the cancer patients. In very broad terms this new intravenous nutrition therapy means that a cancer patient should not be left without specific cancer therapy because of starvation and its serious or even fatal complications.

[General aspects concerning the intravenous feeding of cancer patients]

In order to obtain or maintain a good nutritional status in cancer patients, it is often necessary to perform intravenous nutrition. In summary, several studies have indicated that intravenous nutrition may be beneficial in association with surgery, radiation, or chemotherapy in patients with cancer. More controlled studies, however, are required. There is no indication at the present time of any adverse effects of this method of treatment in relation to tumor growth. The general nutritional improvement in patients on intravenous nutrition increases the immunocompetence, resistance to radiation and cytostatic as well as the mood and quality of life of the cancer patients. In very broad terms this new intravenous nutrition therapy means that a cancer patient should not be left without specific cancer therapy because of starvation and its serious or even fatal complications.

[Complete parenteral nutrition of amino acids, glucose, vitamins and minerals with inclusion of fats]

The objective of complete intravenous nutrition is to supply by the intravenous route all the nutrients normally obtained in the oral diet and the same relative proportions as absorbed from an oral diet. Some suggested allowances to meet these nutritional requirements in patients with different clinical conditions are made. There appears to be little overall difference in the clinical effectiveness of an intravenous regime in which all the non-protein energy is provided by glucose and one in which both glucose and lipid are used. However, the use of a system of complete intravenous nutrition, which by definition must contain lipid, does have specific practical advantages which make it the system of choice in certain circumstances.

A perfluorochemical oxygen carrier (fluosol-43) in a synthetic medium used for perfusion of isolated rat liver

An emulsion of perfluorotributylamine (Fluosol-43) was used as substitute for the gas-carrying function of erythrocytes in a synthetic medium for perfusion of isolated rat liver. The efficiency and effect of this synthetic gas-carrier were evaluated from measurements of the concentrations of rat albumin, the unsaturated vitamin B12-binding capacity of small-molecular-size vitamin B12-binding proteins (UBBC of SBP), urea nitrogen, glucose, sodium, potassium, alanine amino transferase (ALAT) in the medium, and the incorporation of 14C-lysine into the circulating proteins. Secretion of bile, portal pressure, PO2, PCO2 and pH in the affluent and the effluent mediums were also measured. The results demonstrate that the oxygen-carrying capacity of the medium and the metabolic functions of the liver were higher, and the liver damage less, when the medium included Fluosol-43 than without it. The albumin synthesis and the secretion of bile were as high as has been reported for perfusions with erythrocytes. This indicates that the oxygen carried by the Fluosol-43 was utilised by the liver, and that the metabolic functions were not adversely affected during 4 h of perfusion by the medium containing Fluosol-43.

Studies on isolated rat liver perfused by perfluoro-compound emulsion

Isolated rat livers were perfused for 6 hours by different types of cell-free synthetic media. Some of the media included perfluoro-compounds as an oxygen carrier. The value of the perfusion medium as blood substitute was judged on the basis of observations and measurements of a number of parameters. These were: secretion of bile, fluid pressure in the portal vein, the level of GPT (ALAT) transaminase, urea nitrogen, and glucose in the perfusate. The rate of albumin synthesis and the rate of 14-C-lysine incorporated into circulating proteins were also measured. It was found that perfusion of the isolated rat liver with the TC-199 Difco medium containing the perfluoro-compound FC-80 emulsion maintained the liver in a good condition demonstrated, among other things, by the synthesis of albumin and other proteins. The liver could be kept in a good functional condition during 6 hours perfusion with this cell-free medium. With all the other types of perfusate tested the liver did not synthesize proteins. The isolated rat liver seems to be both convenient and advantageous for testing the perfusion media with respect to their capacity to maintain important metabolic functions.

Vollständige parenterale Ernährung

Ausgedehnte experimentelle und klinische Untersuchungen haben ergeben, dass man eine vollständige intravenöse Ernährung mit Hilfe von Aminosäuregemischen, Glukose oder Fruktose, Fett-emulsionen, Elektrolyten und Vitaminen durchführen kann. Mit dieser Alternative zur oralen Nahrungsaufnahme ist es möglich, bei Patienten, bei denen eine orale Nahrungszufuhr unmöglich oder nicht angezeigt ist, einen guten Ernährungszustand zu erreichen und das Wachstum bei Kindern über längere Zeit zu gewährleisten. Durch die parenterale Ernährung ist es bei Kleinkindern und Säug-lingen einerseits möglich, postoperative Körpereiweiss- und Ge-wichtsverluste zu verhindern und andererseits die Neubildung von Körpereiweiss anzuregen und das Wachstum zu fördern. Manche Fragen, die mit der parenteralen Ernährung in Zusammen-hang stehen, müssen im Laufe ihrer weiteren Anwendung noch be-antwortet werden, wie z. B. Fragen der optimalen und maximalen Fettzufuhr, der optimalen Zusammensetzung von Aminosäuregemischen und des Energie-Nährstoffbedarfes. Unser heutiges Wissen über eine vollständige parenterale Ernährung ist jedoch so weit-reichend, um eine Mangelernährung, wie sie als Begleitsymptom bei den verschiedensten inneren und chirurgischen Erkrankungen auf-zutreten pflegt, ausschalten zu können.