The effect of isotonic amino acid infusions on serum proteins and muscle breakdown following surgery

An Evaluation of Peripheral Essential Amino Acid Infusion following Major Surgery

To assess postoperative progress 43 patients undergoing major abdominal procedures were randomized to be given normal postoperative electrolyte solutions alone or with the addition of 400 ml of essential amino acids. Postoperative measurements confirmed a nitrogen retention significant at 0.1%. Decreased breakdown of muscle was also shown by measuring the upper arm muscle circumference and by following the grip strength. Those treated had no significant muscle loss postoperatively but there was significant loss in those not receiving amino acids. The intravenous cannulae survived equally well in both groups. There was no demonstrable difference in the overall clinical progress.

Nutrition Society Symposium on ‘End points in clinical nutrition trials’ Death, morbidity and economics are the only end points for trials

In order to determine whether surrogate markers predict clinical outcome, randomized controlled trials (RCT) of nutrition supportv. no nutrition support that have reported at least one clinical outcome (mortality, infections, total complications, or duration of hospitalization) and at least one nutritional outcome (energy or protein intake, weight gain, N balance, albumin, prealbumin, transferrin, three anthropometric measures, skin testing, lymphocyte count) were assessed for concordance. If changes in nutritional markers predict clinical outcome, changes in both outcomes should go in the same direction. Concordance is defined as both outcomes changing in the same direction or both outcomes showing no difference. Discordance is defined as one outcome changing and the other not (partial) or both outcomes changing in opposite directions (complete). Ninety-nine RCT were identified, of which most were underpowered to see statistically significant changes, especially in clinical outcomes. Thus, the results were analysed only in relation to the direction of the respective changes in outcomes. Forty-eight comparisons (4×12) were made. The rates of concordance were ≤50% in forty-one of forty-eight comparisons; the rate was never >75%. A complete discordance rate of ≥25% was present in forty-three (≥50% in thirteen) of the forty-eight comparisons. The discordance was usually a result of the nutritional outcome being better than the clinical outcome. Changes in nutritional markers do not predict clinical outcomes. Before adopting any surrogate marker as an end point for a clinical trial, it has to be known that improving it will result in patient benefit.

Nutrition in the perioperative patient

The association of malnutrition with surgical morbidity and mortality is well recognized. The question of whether this relationship is causal or simply an association in sick patients has been hotly debated. The field of nutrition support has grown out of the belief that correcting malnutrition will modify associated risks for poor outcome. It has been easier to substantiate this belief in some clinical situations than in others. The evidence for nutrition support during the perioperative period is reviewed and recommendations are made about where nutrition support is most useful and where it may be counterproductive. Some of the important unanswered questions about perioperative nutrition support are raised.

AGA technical review on parenteral nutrition

This literature review and the recommendations therein were prepared for the American Gastroenterological Association Clinical Practice and Practice Economics Committee. The paper was approved by the Committee on September 13, 2001, and by the AGA Governing Board on May 18, 2001.

Nutritional support in the critically ill patients. A critical review of the evidence

Providing nutritional support has become a standard component of managing critically ill patients. While many studies have documented that providing nutritional support can change nutritional outcomes (e.g., amino acid profile, weight gain, nitrogen balance), data are lacking that demonstrate that nutrition actually influences clinically importance endpoints. This article systematically reviews and critically appraises the literature, examining the relationship between nutritional support and infectious morbidity and mortality in the critically ill patient. In addition, evidence-based recommendations are made.

Maintaining muscle protein anabolism after a metabolic stress: role of dextrose vs. amino acid availability

The effect of chronic hypocaloric parenteral infusions of amino acids (AA) vs. dextrose (D) on protein homeostasis after a generalized metabolic stress was examined. Multicatheterized mongrel dogs were metabolically challenged by a 4-day fast and then administered a 4-day intravenous infusion of saline (S, n = 8), D (n = 8), or isocaloric AA (n = 7). Although nitrogen balance (g.kg.1.day-1) was similarly negative with S (-0.37 +/- 0.05), D (-0.28 +/- 0.03), and AA (-0.37 +/- 0.04) during the fasting period, it was less negative (P < or = 0.05) with AA (-0.06 +/- 0.04) than with D (-0.20 +/- 0.03) or S (-0.23 +/- 0.04) during nutrient infusion. AA resulted in net hindlimb uptake and D in net hindlimb release of essential AA (570 +/- 261 vs. -248 +/- 59 nmol.kg-1.min-1). Whereas S and D infusions led to net hindlimb muscle protein loss (-37 +/- 24 and -89 +/- 33 micrograms.kg-1.min-1, respectively, P < or = 0.05 vs. AA), parenteral AA resulted in net deposition (169 +/- 62 micrograms.kg-1.min-1) as measured using L-[ring-2H5]phenylalanine. Thus hypocaloric parenteral D infusion after a metabolic stress does not favor nitrogen conservation, because net whole body nitrogen loss, skeletal muscle protein catabolism, and hindlimb AA release were not blunted compared with S infusion. Conversely, hypocaloric AA infusion preserves whole body and muscle protein stores.

[In which patients and for which procedures has the efficacy of postoperative artificial nutrition be proven?]

This study reviewed 19 prospective studies for the incidence of postoperative nutritional support on outcome in elective surgery. It compared enteral and parenteral nutrition initiated no more than three days preoperatively or postoperatively and prolonged maximally for one month, to a simple infusion of glucose or saline. As all studies had methodological weaknesses, concerning mainly the sample size, it is impossible to propose relevant recommendations. Nevertheless, among the 11 studies on total parenteral nutritional support (nitrogen and caloric supply with carbohydrates and/or lipids), three of them produced valuable results. As the available data do not show any beneficial effect, a routine postoperative nutritional support cannot be recommended, even in patients at high risk of postoperative complications. However for the latter a possible benefit cannot be totally excluded in some of them. When an alimentation per mouth cannot be started during the 8 to 10 days after surgery, an artificial nutritional support becomes mandatory.

Plasma-specific proteins: their response to surgical trauma and tumour load, and modification of this response by post-operative metabolic support

Concentrations of plasma proteins with short half-life have been suggested as indicators of nutritional state in surgical patients. Trauma also affects the circulating concentrations of these proteins. Serum concentrations of retinol binding protein (RBP), pre-albumin and transferrin were determined pre- and post-operatively on different supporting regimens. The circulating concentration of these liver proteins displayed no differential effect of the supporting regimen during the first 5 post-operative days. None of the patients with tumour demonstrated any indication of hepatic metastases pre-operatively or at the time of laparotomy but, as a group, had lower pre-operative concentrations of RBP (p < 0.001) and pre-albumin (p < 0.01) than patients with no tumour load. In addition 55% of patients (15:27) with tumour had RBP concentrations <3.5 mg/dl; all of the non-tumour bearing patients (13/13) had RBP concentrations >3.5 mg/dl. RBP and pre-albumin appear to act as non-specific tumour markers, but not to serve a useful function as short-term nutritional markers of post-operative support.

The utilisation of peripherally-administered intravenous nutrient solutions

The utilisation of three peripherally-administered intravenous nutritional regimens has been evaluated in 42 patients on the first four days following surgery for colorectal cancer. A standard dextrose-saline (DS) regimen (n = 16) has been compared with an amino-acid (AA) regimen (n = 12) and a regimen consisting of glucose, amino-acid and fat (GAF) (n = 14). Fat and carbohydrate oxidation was calculated pre- and post-operatively using indirect calorimetry. Patients receiving AA showed a fall in carbohydrate oxidation (p < 0.01) and a rise in fat oxidation (p < 0.05) post-operatively, whereas no significant changes in fat and carbohydrate oxidation occurred in the DS and GAF groups. Cumulative nitrogen balance (NB) for the first four post-operative days was significantly better (p < 0.01) in the AA group (-10.3 +/- 3.8 g; mean +/- s.e.m.) than in the DS group (-25.3 +/- 3.1 g), due to an improved NB in the AA group on the first and second days only. Cumulative NB in the GAF group (+7.7 +/- 2.3 g) was significantly better (p < 0.01) than in the other two groups. Where the provision of peripheral intravenous nutritional support is desired, the use of a combination of glucose, amino-acid and fat is recommended.

The effects of an anabolic steroid and peripherally administered intravenous nutrition in the early postoperative period

Sixty patients undergoing colorectal surgery for malignancy were randomized to receive the anabolic steroid stanozolol (n = 30) or to a control group (n = 30). Patients were further randomized to receive on the first 4 postoperative days a) a standard dextrose-saline regimen (DS), b) an amino acid regimen (AA), or c) a glucose-amino acid-fat regimen (GAF) via a peripheral vein. Fat and carbohydrate oxidation rates were calculated pre- and postoperatively using indirect calorimetry. Postoperative nitrogen balance (NB) in patients receiving amino acids was significantly improved (p less than 0.02) by the administration of stanozolol. Fat and carbohydrate oxidation rates were not significantly affected by stanozolol. Patients in the stanozolol and control AA groups showed a fall in carbohydrate oxidation (p less than 0.01) and a rise in fat oxidation (p less than 0.05) postoperatively, whereas no significant changes in fat and carbohydrate oxidation occurred in the two DS and two GAF groups. Cumulative NB for the first 4 postoperative days was significantly better (p less than 0.01) in the two AA groups than in the two DS groups, due to an improved NB in the two AA groups on the 1st and 2nd days only. Cumulative NB in the two GAF groups was significantly better (p less than 0.01) than in all the other groups. This study shows that stanozolol improves postoperative NB in patients receiving amino acids alone, whereas the provision of a more complete nutritional regimen containing glucose, amino acids, and fat results in a positive NB unaffected by stanozolol.

Nutritional support: how much for how much?

Although malnutrition is associated with poor clinical outcome, it cannot be inferred that better nutrition will improve clinical outcome. Efficacy of a proposed regimen is best established by prospective, randomised, controlled trials. Cost effectiveness is only an issue if efficacy exists. Patients with long term temporary, or permanent, inadequate bowel syndrome are candidates for parenteral nutrition. Most of the prospective, randomised, controlled trials testing the value of nutritional support in other diseases, however, have failed to show that this treatment has a beneficial clinical effect. Areas where these trials have shown a possible clinical benefit include the perioperative care of patients with upper gastrointestinal cancer, elemental diet treatment of Crohn's disease, and branched chain amino acid infusions in hepatic encephalopathy. Even in these instances, it is not clear that such treatment will prove to be cost effective (compared with other currently available treatments).

Lack of modulation of postoperative immunosuppression by isotonic amino acid infusion

Effects of an isotonic amino acid solution on the immune defence systems of surgical patients were studied. Twenty-two patients admitted for major abdominal operations were randomly allocated into two groups. Eleven of them received 1 liter of 3% amino acid solution daily for 5 days postoperatively, while 11 control patients received balanced 5% glucose-containing electrolyte solutions. Immune variables were studied preoperatively and at 1, 3 to 4, and 6 to 7 days postoperatively. These studies included leukocyte and differential counts, T (OKT3+), B (sIg+), T helper/inducer (OKT4+) and suppressor/cytotoxic (OKT8+) cell determinations, measurement of in vitro lymphocytic responses to phytohemagglutinin (PHA), pokeweed mitogen (PWM) and Staphylococcus aureus Cowan I (StaCw) in cultures of separated lymphocytes, and to PHA, concanavalin A (Con A), and PWM in whole blood cultures. B lymphocyte functions were studied by measuring synthesis of immunoglobulins IgG, IgM, and IgA in the cell culture medium when lymphocytes were stimulated with PWM alone and in the presence of Con A or hydrocortisone. Postoperative amino acid infusion slightly improved the capacity of lymphocytes to synthetize and secrete IgG and IgM. By contrast, no improvement was seen in cell counts or lymphocyte transformation patterns.

Modification of postoperative nitrogen balance with preoperative anabolic steroid

Thirty six patients undergoing abdominal operations were randomly allocated to receive an anabolic steroid, stanozolol (50 mg) or placebo 24 h before surgery. Patients were fasted during the first four postoperative days. During this period the mean daily nitrogen balance was significantly less negative in the stanozolol group (-8.0+/-3.0 gN/day) than in the control group (-10.9+/-4.1 gN/day), although improvement in nitrogen balance was greater in male than in female patients. Muscle catabolism as measured by 3-methylhistidine excretion was similar in both treatment groups. Significant fluid retention occurred in the stanozolol treated group and was more marked in female patients. Improved nitrogen balance in the absence of a measurable change in muscle catabolism suggests that this anabolic steroid acts by improving protein synthesis in the early period after surgery.