Intravenous amino acids as the sole nutritional substrate. Utilization and metabolism in fasting normal human subjects

Nutrition in critical care

Critical care has evolved from a prolonged recovery room stay for cardiac surgery patients to a full medical and nursing specialty in the last 5 decades. The ability to feed patients who cannot eat has evolved from impossible to routine clinical practice in the last 4 decades. Nutrition in critically ill patients based on measurement of metabolism has evolved from a research activity to clinical practice in the last 3 decades. The authors have been involved in this evolution and this article discusses past, present, and likely future practices in nutrition in critically ill patients.

Advances in hospital nutrition

The General Clinical Research Center facilities have been largely responsible for expansion of knowledge in the field of hospital nutrition. Expansion of this knowledge base has led to major medical advances in this century. Without the meticulous attention necessary for metabolic balance studies many if not most of these advances would have been seriously delayed. The role that General Clinical Research Centers have played and will continue to play cannot be overestimated.

Parenteral nourishment of patients undergoing surgical or traumatic stress

Severe surgical or other traumatic stress initiates an integrated central nervous system and metabolic response characterized by catabolism which selectively preserves vital organs, drawing on peripheral tissue proteins for required amino acids. When oral intake is prohibited adequate intravenous nutritional support hastens convalescence and may be life-saving. Intravenous nutrients routinely consist of amino acids for replacement of lost protein, a nonprotein calorie source--usually glucose, and vitamins and minerals. Lipid, infrequently used in routine surgery as part of the calorie source, supplies essential fatty acids and prevents side effects resulting with large amounts of intravenous glucose. Lipid has other benefits. Stress-induced hormones stimulate lipid catabolism. When lipid is used for part of the calorie requirement in intravenous feedings, the plasma insulin level is reduced and peripheral amino acids become available for synthesis of critically needed visceral proteins. Recent work has shown that the branched chain amino acids carnitine and some species of lipid added to intravenous nutrient formulations postoperatively affect the nitrogen retention and may hasten convalescence. Further work should be directed at understanding the unique biochemical changes occurring after injury, devising objective assay procedures to measure the severity of the response and improving intravenous formulations for the acutely ill surgical patient.

Fasting plasma amino acid levels in cancer patients

The concentration in plasma of 15 fasting amino acids were measured in 14 control volunteers and 55 cancer patients. In addition, 16 patients (7 with, 9 without total parenteral nutrition [TPN] ) with metastatic sarcoma had sequential amino acid profiles measured during 6 weeks of ablative chemotherapy. In four cancer patient groups (lymphoma, sarcoma, osteosarcoma and metastatic sarcoma) with no or minimal weight loss, most plasma amino acid levels were similar to controls. Proline levels were significantly reduced in the lymphoma and sarcoma patients. Esophageal cancer patients with 20% body weight loss had a marked reduction in total and individual amino acid levels (except branched chain amino acids) compared to controls and all others. The metastatic sarcoma patients who received parenteral nutrition had higher levels of plasma lysine and tyrosine during chemotherapy than controls; however, TPN failed to change the majority of amino acid levels. It appears that plasma amino acid levels except proline were well maintained in cancer patients without weight loss. Esophageal cancer patients with weight loss demonstrated marked reduction in all circulating amino acids except branched chain. Parenteral nutrition did not significantly alter the amino acid profile of cancer patients undergoing chemotherapy.

Abnormal plasma amino acid profiles in patients undergoing bone marrow transplant

Amino acid concentrations in plasma have been measured during total parenteral nutrition in patients undergoing bone marrow transplantation. Profound hyperaminoacidemia was noted in the immediate para-transplant period. The increase was due mainly to high levels of phenylalanine and methionine. During the radiation treatment period these amino acids plus valine, proline, serine and glycine were exceptionally high. Levels of cystine and asparagine tended to be low. The results suggest that infusion of a mixture of amino acids which is lower in phenylalanine and methionine might result in better nitrogen utilization.

Peripheral vein complications in patients receiving amino acid/dextrose solutions

The incidence and severity of peripheral vein phlebitis was evaluated in patients receiving infusions of amino acids alone (1.4 g/kg/day) (group I), amino acids (1.4 g/kg/day) plus 5% dextrose (group II) and 5% dextrose alone (Group III). Ninety-three patients with carcinoma of the bladder were randomized to receive one of three peripheral parenteral nutrition solutions which were infused predominantly via scalp-vein needles. Peripheral parenteral nutrition solutions contained sodium and potassium chloride as necessary to maintain normal serum electrolyte levels. The osmolality of each solution was calculated. Peripheral intravenous sites were evaluated every 8 hr and at the time of each intravenous site change. The incidence of infiltration, phlebitis and its' severity was recorded and graded zero (no complications) to 4 (severe complications). An intravenous cannula was discontinued if infiltration or a grade 2 or greater phlebitis occurred. The mean osmolality of the solutions were (group I) 450 to 500 mosm/liter, (group II) 713 to 763 mosm/liter and (group III) 369 mosm/liter. The mean duration of infusion was 9.0 + 0.4, 9.1 + 0.4, and 8.7 + 0.5 days, respectively, and the mean number of intravenous site changes were 6.1 + 0.3, 5.8 + 0.3, and 5.6 + 0.3, respectively. Infiltration preceded 57, 56, and 58% of all intravenous site changes and the incidence and severity of peripheral vein phlebitis was similar for all three groups. Sixty patients who received their infusions via plastic indwelling catheters for a mean duration of 2.6 + 1.0, 2,3 + 1.0, and 2.8 + 1.0 days had an 86, 71, and 76% incidence of grade two or greater phlebitis, respectively. There was no significant difference in the incidence of infiltration and phlebitis in patients receiving peripheral parenteral infusions of amino acids alone, amino acids plus dextrose, and 5% dextrose alone.

The effects of nitrogen and energy intake on the metabolism of normal, depleted and injured man: Considerations for practical nutritional support

This article illustrates how the nutritional and metabolic effects of a range of protein and energy intakes depend on the clinical state of the patient and how these considerations may be used to provide guidelines for nutritional support. First, it is necessary to define states and mechanisms of malnutrition and then discuss the biochemical processes which underlie nutritional rehabilitation.

[Enzymatic changes and protein metabolism in the early and late postoperative phase during intravenous feeding]

119 metabolically healthy surgical patients, who had to undergo elective intraabdominal surgery, were separated into upper - cholecystectomy, gastric resection - and lower - colonic and sigma surgery - intraabdominal procedures and divided into 8 groups with different infusion regimens. During the early postoperative period, patients with upper abdominal surgery had significantly higher postoperative enzyme changes compared with patients with lower abdominal surgery. Patients with cholecystectomy had the significantly highest postoperative enzyme changes. On postoperative day 6 the enzyme changes showed a significant dependence from the duration of total parenteral nutrition, the chosen calorie-nitrogen ratio, and the chosen energy substrate, Xylitol or glucose. We could show a significant negative correlation between the extent of the stimulation of hepatic lipid synthesis and the protein parameters. Of all chosen infusion regimens, Xylitol in a dosis of 0.11 g/kg BW x h together with the high amino acid infusion rate of 1.76 g/kg BW x day had the most favourable effect on the extent of stimulation of hepatic lipid synthesis, the late postoperative enzyme changes, and the synthesis rate of visceral proteins. This study could demonstrate that different intraabdominal surgical procedures need a more specific nutritional therapy.

Alanine turnover in the postabsorptive state and during parenteral hyperalimentation before and after surgery

Influence of total parenteral nutrition and operation on alanine turnover and venous alanine concentration was determined in 5 patients with stomach carcinoma using single technique of U-14C alanine. Every patient served at his own control. In the postabsorptive state alanine turnover was 1.63 +/- 0.31 mgatC . min-1, not different from a control group (1.84 +/- 0.60 mgatC . min-1); during total parenteral nutrition alanine turnover increased to 3.21 +/- 0.5g mgatC . min-1 with a rise in alanine concentration from 0.96 +/- 0.17 mgatC . L-1 + 0.69 +/- 0.22 mgatC . L-1. After surgery during the same total parenteral nutrition alanine turnover increased further to 3.78 +/- 0.17 mgatC . min-1 with a lowering of alanine concentration to 1.44 +/- 0.22 mgatC . L-1. The present results show the distinct influence of TPH on alanine kinetics. The present data indicate that alanine turnover cannot be deduced from blood alanine concentration.

A controlled study of protein-sparing therapy after excision of the rectum: effects of intravenous amino acids and hyperalimentation on body composition and plasma amino acids

This study considers the effects of glucose, during amino acid infusion, on protein-sparing and amino acid utilization after proctocolectomy or abdominoperineal resection of the rectum. Body composition and plasma amino acids were compared in each of three groups of patients before and 15 days after surgery who were receiving, in addition to restricted oral diets: 1) no hyperalimentation 2) parenteral amino acids or 3) hypertonic glucose plus amino acids. Parenteral solutions were given by central venous catheter. Infusion of amino acids alone spared body protein but branch chain amino acids (i.e. valine, isoleucine and leucine) and also phenylalanine, methionine and proline were increased well above the normal values. There were no increases in liver proteins other than for the "acute phase" type. In contrast, full hyperalimentation spared more body protein and fat, restored plasma amino acids to normal while plasma cortisol and acute pohase proteins were lower. Plasma transferrin, prealbumin and retinol binding protein were increased, as previously shown, while clinical outcome was more favorable. It is concluded that glucose is essential to ensure optimum utilization of amino acids for both muscle and liver protein synthesis and, therefore, intravenous hyperalimentation is preferable to amino acids alone after major colorectal surgery.

The absence of protein--sparing effects utilizing crystalline amino acids in stressed patients

The protein-sparing effects of the peripheral infusion of crystalline amino acids (PAA) was studied metabolically in selected surgical patients subjected to various degrees of stress. Twenty-one patients (sixteen cancer patients receiving chemotherapy and/or radiotherapy, three with major abdominal traumatic injuries and four with paralytic ileus) were infused with 2 1/24 hours of a solution of 4.2% Travasol amino acids with only 5% glucose as a source of nonprotein calories. One-half of the cancer patients were also allowed ad libitum oral intake of a regular hospital diet or Vivonex-HN. The nutritional status was evaluated by measuring changes in body weight, serum albumin levels and nitrogen balance. Body weight decreased in only the trauma patients. When these solutions were the sole source of nutrients all patients were in negative nitrogen balance and had significant decreases in their serum albumin levels. Serum albumin levels were preserved only when extra sources of calories were provided. The infusion of the crystalline amino acids without adequate levels of nonprotein energy did not conserve protein in these stressed patients.