Total parenteral nutrition with lipid

Nitrogen requirements in severely injured patients

The study was designed to evaluate nitrogen needs in severely injured patients during the first week after trauma. Thirty-nine patients aged from 18 to 65 years with a burn or fractures of more than two long bones were studied. Energy requirements were given parenterally as fat and glucose in isocaloric amounts. The patients were randomized into five groups receiving different amounts of nitrogen from zero to 0.3 g kg body-weight-1 24 h-1. Daily and cumulative nitrogen balance, urinary 3-methylhistidine excretion and nitrogen retention were calculated on days 2-8 after trauma. With no nitrogen, the mean(s.e.m.) daily nitrogen balance after the trauma was -13.8(0.5) gN. The balance improved markedly in groups with a nitrogen intake of up to 0.2 g kg body-weight-1 (P less than 0.001) compared with the no-nitrogen group. The 3-methylhistidine excretion increased because of the trauma in all groups with no statistically significant difference between the groups. Nitrogen retention decreased with increase in nitrogen supply and with time after injury. It is suggested that a nitrogen supply of 0.20 kg bodyweight-1 24 h-1 is optimal for severely injured patients during the first week after trauma.

The effect of total parenteral nutrition on hepatic drug oxidation

Hepatic dysfunction is a frequent complication of total parenteral nutrition (TPN), indicated by derangement of standard liver function tests. However, such changes are variable and nonspecific, and represent hepatic injury rather than changes in hepatic function. Antipyrine (Phenazone) clearance is a sensitive indicator of hepatic microsomal enzyme activity and provides a more specific indication of hepatic function. This was used to investigate the effect of different TPN regimens. Patients receiving a postoperative 2000 kcal TPN regimen providing all nonprotein calories as dextrose (n = 16) showed a 34% reduction of mean antipyrine clearance after 7 days of TPN compared to controls (n = 13, p less than 0.05). This effect was seen also in patients receiving a 1600 kcal dextrose-based regimen (n = 8). In patients receiving a 2000 kcal TPN regimen in which 500 kcal were provided as lipid (n = 10), mean antipyrine clearance was not significantly different from that of the control group. This study indicates the sensitivity of hepatic microsomal oxidative function, an important route of drug metabolism, to different TPN regimens.

Alterations in the metabolism of exogenous lipid associated with sepsis

The responses to an exogenous lipid challenge of nonhypermetabolic surgical patients requiring parenteral nutrition and seriously ill septic patients were compared. All patients received a 500-ml intravenous infusion of a 10% lipid emulsion over a 4-hr period. An early elevation of glycerol and triglyceride was noted during the infusion suggesting chylomicron fractionation. Peak triglyceride levels were higher in the septic group but the rate of lipid clearance appeared essentially identical in both septic and nonseptic patients. Lipoprotein lipase levels remained constant and were equal for both groups. Significant late ketone body production was statistically identical in both groups despite depressed albumin levels in the septic group suggesting adequate hepatic ketogenic capacity in septic as well as nonseptic patients.

Energy and protein requirements of general surgical patients requiring intravenous nutrition

General surgical patients require intravenous nutrition either because their gastrointestinal tract is blocked, too short or inflamed or because it cannot cope. Such patients can be grouped into four nutritional/metabolic categories: normal and unstressed; normal and stressed; depleted and unstressed; depleted and stressed. The energy requirements of patients in each of these groups vary according to their energy expenditure. Normally nourished and stressed patients have the highest energy expenditure and therefore require the highest energy input (45-55 kcal.kg-1day-1). Other groups of patients rarely require more than 40 kcal.kg-1day-1. Energy can be given mainly as dextrose although calories needed above 40 kcal kg-1day-1 should be given as fat (unless lipogenesis is desirable). In very stressed patients high rates of glucose infusion can themselves constitute a metabolic stress and fat may play a bigger role as a calorie source. For long term feeding, 1 litre of 10 per cent fat emulsion should be given weekly to avoid essential fatty acid deficiency. The level of nitrogen intake required to maintain a positive nitrogen balance is a lot higher in surgical patients than the suggested recommended dietary allowances for normal subjects. It is dependent not only on the nutritional and clinical state of the patient but also on the levels of energy and nitrogen intake given. When energy intake is below energy needs, normally nourished patients cannot retain nitrogen, although depleted patients can. When energy intake exceeds energy needs, both normally nourished and depleted patients retain nitrogen at levels of nitrogen intake ranging from 250 mg kg-1day-1 (depleted and unstressed) to over 400 mg kg-1day-1 (stressed). Depleted patients can maintain a positive nitrogen balance at lower levels of calorie and nitrogen intake than normally nourished patients and in this respect are analogous to a growing child. In all surgical patients, energy and nitrogen intakes can be manipulated to provide for a controlled maintenance or restoration of either wet lean tissue and/or fat. There is little place for protein sparing therapy or the use of insulin and anabolic steroids to promote nitrogen retention in surgical patients requiring intravenous feeding.

Fat-based (Intralipid 20%) versus carbohydrate-based total parenteral nutrition: effects on hepatic structure and function in rats

The role of fat-based total parenteral nutrition (TPN) in preventing or ameliorating hepatic dysfunction during TPN was investigated. Adult ACI-N rats were given fat-free carbohydrate-based TPN or isocaloric, isonitrogenous fat-based TPN (50% cal from 20% Intralipid, 50% cal from carbohydrate) for 7 days with Purina Chow-fed and fasting rats as controls. After fat-based TPN as compared with Chow or carbohydrate-based TPN, serum alkaline phosphatase activity and cholesterol levels doubled. Fatty infiltration and periportal inflammation in the liver were more marked. Both the TPN regimens were equally effective in maintaining body weight, positive nitrogen balance, muscle and hepatic protein content. Hepatic dysfunction in rats during TPN was not prevented by using a fat emulsion to provide 50% of the caloric requirement; the optimal proportion of fat as energy substrate in this system is less than 50%.

Hormonal changes and their influence on metabolism and nutrition in the critically ill

This is a brief review of the observed hormonal alterations following trauma and sepsis. The major changes noted in the metabolic status of the stressed patient have been characterized by deranged carbohydrate metabolism, altered metabolic rate as measured by oxygen consumption and increased ureagenesis. Each of these phenomena are regulated to a large extent by the specific hormonal profile of the patient. Failure of insulin and growth hormone production have been associated with glucose intolerance, excessive urinary nitrogen loss and a fatal outcome. Glucagon, cortisol and catecholamines exhibit sustained elevation and have been associated with increased metabolic rate and excessive ureagenesis. These changes are usually self limited following trauma but will persist if the patient enters a septic phase. The use of specific nutritional support, namely hypertonic glucose versus a balanced fat emulsion system in the face of sepsis is considered.

Influence of total parenteral nutrition on tissue lipoprotein lipase activity during chronic and acute illness

This study examines the influence of total parenteral nutrition (TPN) compared with 5% dextrose (D5) infusion on skeletal muscle and adipose tissue lipoprotein lipase (LPL) activity in nutritionally depleted, injured and infected patients. The plasma concentrations of glucose, free fatty acid (FFA), triglyceride and insulin were also measured. During TPN, nutritionally depleted subjects showed an increase in adipose tissue LPL activity, "fat cell size," and plasma insulin concentration. Skeletal muscle LPL activity and plasma FFA concentration decreased. In comparison, trauma patients showed a less marked rise in adipose tissue LPL activity and skeletal muscle LPL activity increased. Infected patients had a much smaller rise in adipose tissue LPL activity than either of the other groups, and muscle activity rose. The depleted and injured patients showed a linear relationship between adipose tissue LPL activity and plasma insulin concentration and an inverse hyperbolic relationship between adipose tissue LPL activity and plasma FFA concentration.

Parenteral nutrition by peripheral vein

Peripheral parenteral nutrition can provide perioperative nutritional support to patients with inadequate oral intake in whom total parenteral nutrition with hypertonic dextrose administered by a central vein cannot be undertaken because of sepsis, subclavian vein thrombosis, or lack of expertise and familiarity. Peripheral parenteral nutrition may be indicated in patients with marginal nutritional status whose postoperative course and period of starvation are unpredictable and in patients being started on a total enteral nutrition regimen. In patients with increased requirements because of stress or malnutrition who need full nutritional support by a peripheral method, the lipid system is indicated. In certain instances, large enough volumes can be infused to provide sufficient calories and protein for nutritional repletion. Protein-sparing therapy is indicated for nutritional maintenance in patients who do not clearly require full support by total parenteral nutrition but who are taking insufficient calories and protein orally. Peripheral parenteral nutrition avoids the risks of subclavian vein catheterization but requires that adequate peripheral veins are available. The metabolic complications are minimal compared with those of total parenteral nutrition, and the nutritional management of the diabetic patient is greatly simplified. Several techniques of preserving peripheral veins and prolonging their use have been discussed.

Does intravenous fat spare nitrogen in the injured rat?

The role of glucose versus fat as a source of energy in parenteral nutrition is controversial, particularly when administered after trauma, injury or in sepsis. In the present series of experiments, rats undergoing laparotomy and jugular vein cannulation were infused with hypertonic glucose or Intralipid with and without amino acids. The results demonstrate that the combination of amino acids and glucose has a better nitrogen-conserving ability than amino acids and fat, lasting at least 4 days after injury. However, when infused without amino acids, fat had the same nitrogen-conserving quality as glucose. The authors attribute the improved nitrogen-conserving quality of amino acids and glucose to the specific carbohydrate influence on amino acid metabolism, an action which is specific in both protein-free and protein-containing meals but has only very limited effect in the absence of simultaneously infused or fed amino acids. In the moderately to severely injured rat, a glucose calorie is significantly more effective in sparing nitrogen than a fat calorie.