Elemental balances during intravenous hyperalimentation of underweight adult subjects

Is there a role for parenteral feeding in clinical medicine?

Protein-calorie malnutrition as evidenced by loss of weight or of lean body mass is a commonly seen disorder. Although its cause is clearly multifactorial, objective measures of protein-calorie malnutrition have been repeatedly correlated with poor patient outcomes. Total parenteral nutrition was developed to halt or reverse this disorder, but its ability to improve the short- to intermediate-term outcome in patients with impaired nutrient intake has been highly inconsistent. Factors influencing this variable outcome include the degree of functional impairment in the treatment group, the underlying disease causing the impaired intake, and possibly the amount and composition of nonprotein calories delivered. In particular, considerable evidence points to intravenous soybean oil emulsion as a negative factor in the nutritional support of stressed patients. Taken in combination, current information suggests reserving the use of parenteral feeding for patients meeting objective criteria for protein-calorie malnutrition and making parsimonious use of lipid emulsion, especially in stressed patients.

Expanded gentamicin volume of distribution in critically ill adult patients receiving total parenteral nutrition

Aminoglycoside antibiotics distribute into the extracellular fluid compartment and are eliminated by the kidney via glomerular filtration. Malnutrition and total parenteral nutrition influence the fluid and electrolyte status of the patient, and cause organ changes. The purpose of this clinical study was to characterize the kinetic behaviour of gentamicin in the parenterally fed critically ill adult patient. Eighty-six critically ill adult patients treated with gentamicin for severe Gram-negative infections were enrolled in the study (mean +/- SD): age, 60 +/- 14 years; weight, 69.4 +/- 10.2 kg; height, 163 +/- 10 cm; 22 females and 64 males. Four study groups were defined (2 x 2): total parenteral nutrition vs. fluid therapy, and acute renal failure vs. normal renal function. The drug was administered by intermittent intravenous infusion. Blood samples were drawn at steady-state, 5 min before the next dose ('trough') and 30 min after the termination of the infusion ('peak'). Gentamicin serum concentration was determined by fluorescence polarization immunoassay. Gentamicin pharmacokinetic parameters were estimated by non-linear regression analysis, assuming a one-compartment model and first-order elimination from the central compartment. Treatment of malnutrition with total parenteral nutrition increased gentamicin volume of distribution (P < 0.001), but did not affect total body clearance (P = 0.75). This change tended to produce lower peak concentrations (< 4 micrograms/ml, P = 0.07), thus potentially compromising therapeutic effectiveness. There was no significant influence on trough concentrations (P = 0.56). Patients receiving fluid therapy had a volume of distribution of 0.34 +/- 0.08 litre/kg, while those fed by the intravenous route showed larger values (0.43 +/- 0.12 litre/kg), irrespective of their renal function. This may be explained by the extracellular water expansion caused by stress, malnutrition, and parenteral refeeding. Gentamicin dosage regimens in critically ill adult patients on total parenteral nutrition should be formulated on the basis of larger volumes of distribution and to attain therapeutic serum concentrations higher doses may be required.

Amino acid and energy needs of pediatric patients receiving parenteral nutrition

The technique of parenteral nutrition has become such an established part of modern pediatric care that it is difficult to imagine how pediatricians, as recently as 25 years ago, managed a large group of very difficult patients; however, despite its obvious nutritional advantages, the technique is not without problems. Many of these can be circumvented or controlled by careful attention to all aspects of the technique. Certainly the incidence of these problems can be maintained at a level sufficiently low that the benefits of the technique far outweigh its risks; however, the technique clearly can be further improved. One requirement for doing so is to recognize that the technique is deceptively simple and that it should not be used indiscriminantly without careful consideration of indications and alternative strategies for nutritional management. Additional research also is required. As discussed earlier, the available parenteral amino acid mixtures and lipid emulsions, although considerably improved over earlier versions, remain far from optimal. Some of the actual and theoretic problems that should be addressed in the near future are discussed in the preceding sections; there also are many others.

Critically-ill patients receiving total parenteral nutrition show altered amikacin pharmacokinetics

The purpose of this clinical study was to characterise the kinetic behavior of amikacin in the parenterally-fed critically-ill adult patient. 22 critically-ill adult patients treated with amikacin (15.5 +/- 7.9 mg/kg/day) for severe gram-negative infections were enrolled into a non-randomised control trial. Malnourished patients were administered total parenteral nutrition (TPN, n = 11), while well-nourished patients received fluid therapy (FT, n = 11). Amikacin pharmacokinetic parameters were estimated by non-linear regression analysis, assuming a one-compartment model and central first-order elimination. Patients receiving TPN showed an expanded amikacin distribution volume (0.403 +/- 0.0961/kg vs. FT 0.298 +/- 0.083 l/kg, p < 0.05), and a tendency towards increased total body clearance (0.089 +/- 0.029 l/kg/h vs. FT 0.069 +/- 0.0201/kg/h, p = 0.09). TPN produced lower peak concentrations (19.3 +/- 3.1 mcg/ml vs. 23.1 +/- 3.5 mcg/ml, p < 0.05), but had no significant influence on trough concentrations (p = 0.56). Patients on TPN also showed increased body temperature (p < 0.05) and fluid intake (p < 0.05), and decreased hematocrit (p < 0.05). Stress, malnutrition, parenteral nutrition itself, fluid and osmotic overload, and fever often occur concurrently in parenterally-fed patients and appear to produce lower amikacin serum levels. Consequently, critically-ill patients receiving TPN need higher amikacin doses and individualised treatment by monitoring serum concentrations, to ensure optimal therapeutic response.

Nutrition support in critical illness

Sepsis, shock, multiple trauma, and burns are often associated with altered metabolism characterized by severe catabolism, wasting of the lean body mass, immune dysfunction, and compromised wound healing. Nutrition support is one of the mainstays in the management of these critically ill patients and is aimed at minimizing these complications. The purpose of this article is to compare stress hypermetabolism and starvation metabolism, to review current recommendations for the provision of energy and substrate to the critically ill patient, and to review pertinent literature regarding enteral vs parenteral nutrition. Finally, this article will provide a brief overview of new and future therapies with emphasis on specific substrates and growth factors and the potential for their use in the critically ill patient.

Influence of calorie source on the physiological response to parenteral nutrition in malnourished rabbits

The present study was designed to investigate whether calorie source influences sodium and water metabolism and sympathetic activity during parenteral nutrition (PN). 20 New Zealand rabbits were starved until a mean weight loss of 18% was achieved and then re-fed for 6 days with 2 formulae of PN with different glucose-fat proportions. In the Glucose group (n = 9), 70% of non-protein calories were given as glucose while in the Lipid group (n = 11), 70% of non-protein calories were administered as lipids. Rabbits with a high glucose intake showed significantly higher weight gain (151 +/- 87 vs. 52 +/- 7 g, P = 0.01), water cumulative balance (542 +/- 132 vs. 411 +/- 87 ml; P = 0.02) and urinary metanephrine excretion (0.42 +/- 0.12 vs. 0.30 +/- 0.1 mumol/d, P = .03). Only in this group, urinary metanephrines correlated positively with water and sodium balances (r2 = 0.6; P = 0.02 and r2 = 0.7; P = 0.009 respectively). The Glucose group showed 2 different responses and in a second experiment 10 additional rabbits were added to this group to allow a statistical analysis of the response pattern: half of the animals increased their extracellular water (ECW) compartment while the remaining animals did not. The former group had higher sodium balance (13.9 +/- 8 vs. 4.3 +/- 5; P = 0.004) and wet lung weight (8.9 +/- 0.9 vs. 7.9 +/- 0.8; P < 0.05) after re-feeding and, at the beginning of PN, their serum aldosterone concentration were also higher (221 +/- 11 vs. 130 +/- 47 pmol/l; P < 0.05). In conclusion, glucose based PN appears to increase sympathetic activity and induce spurious weight gain due to markedly positive wate and sodium balances. Plasma aldosterone concentration at the end of starvation period influences sodium retention and ECW expansion during high glucose re-feeding.

Anabolic therapy with growth hormone accelerates protein gain in surgical patients requiring nutritional rehabilitation

OBJECTIVE

The authors investigated the effects of exogenous growth hormone (GH) on protein accretion and the composition of weight gain in a group of stable, nutritionally compromised postoperative patients receiving standard hypercaloric nutritional therapy.

SUMMARY BACKGROUND DATA

A significant loss of body protein impairs normal physiologic functions and is associated with increased postoperative complications and prolonged hospitalization. Previous studies have demonstrated that standard methods of nutritional support enhance the deposition of fat and extracellular water but are ineffective in repleting body protein.

METHODS

Fourteen patients requiring long-term nutritional support for severe gastrointestinal dysfunction received standard nutritional therapy (STD) providing approximately 50 kcal/kg/day and 2 g of protein/kg/day during an initial 7-day equilibrium period. The patients then continued on STD (n = 4) or, in addition, received GH 0.14 mg/kg/day (n = 10). On day 7 of the equilibrium period and again after 3 weeks of treatment, the components of body weight were determined; these included body fat, mineral content, lean (nonfat and nonmineral-containing tissue) mass, total body water, extracellular water (ECW), and body protein. Daily and cumulative nutrient balance and substrate oxidation studies determined the distribution, efficiency, and utilization of calories for protein, fat, and carbohydrate deposition.

RESULTS

The GH-treated patients gained minimal body fat but had significantly more lean mass (4.311 +/- 0.6 kg vs. 1.988 +/- 0.2 kg, p < or = 0.03) and more protein (1.417 +/- 0.3 kg vs. 0.086 +/- 0.1 kg, p < or = 0.03) than did the STD-treated patients. The increase in lean mass was not associated with an inappropriate expansion of ECW. In contrast, patients receiving STD therapy tended to deposit a greater proportion of body weight as ECW and significantly more fat than did GH-treated patients (1.004 +/- 0.3 kg vs. 0.129 +/- 0.2 kg, p < 0.05). GH administration altered substrate oxidation (respiratory quotient = 0.94 +/- 0.02 GH vs. 1.17 +/- 0.05 STD, p < or = 0.0002) and the use of available energy, resulting in a 66% increase in the efficiency of protein deposition (13.37 +/- 0.8 g/1000 kcal vs. 8.04 g +/- 3.06 g/1000 kcal, p < or = 0.04).

CONCLUSIONS

GH administration accelerated protein gain in stable adult patients receiving aggressive nutritional therapy without a significant increase in body fat or a disproportionate expansion of ECW. GH therapy accelerated nutritional repletion and, therefore, may shorten the convalescence of the malnourished patient requiring a major surgical procedure.

Extracellular fluid expansion during parenteral refeeding

Life emerged on our planet from a fluid environment which probably contained a similar concentration of sodium and other electrolytes to that of the extracellular fluid of mammals (1). The maintenance of the volume and composition (homeostasis) of this internal fluid surrounding all the body cells is essential for survival. Malnutrition and illness are associated with alterations in the distribution and in the renal handling of water and sodium within the body (2). Thus, an understanding of water and salt physiology is essential for the proper practice of nutritional support.

The nature of nutritional deficiency in relation to growth failure and poverty

A new classification of essential nutrients is proposed based on whether the major response to a deficiency is either (a) specific defects which lead to loss of particular functions and characteristic clinical signs and symptoms or (b) a primary cessation of growth. Diagnosis of deficiency of the nutrients which give rise to growth failure (nitrogen, essential amino acids, potassium, sodium, phosphorus, sulphur, zinc, magnesium) is particularly difficult because of the nature of the response and the lack of a body store. The implications of the differences in the types of deficiency are explored in relation to assessment of the likelihood that widespread deficiency exists. Poverty is particularly likely to be associated with unrecognised deficiency of these "growth" nutrients because of the monotony of the diet. This will lead to slow growth. There is probably a difference in the nutrient requirements for longitudinal and ponderal growth. Of the growth nutrients sulphur is likely to be required in much higher amounts for skeletal growth than soft tissue growth.

Overzealous resuscitation of an extremely malnourished patient with nutritional cardiomyopathy

Overzealous resuscitation of the severely malnourished patient may be associated with life-threatening complications. A variety of electrolyte, hemodynamic, septic, and nutritional derangements may result in sudden decompensation and even death. We present a case that dramatically illustrates these complications and focuses on the key role of underlying nutritional cardiomyopathy.

A clinical application of exercise physiology and nutritional support for the mechanically ventilated patient

A challenging problem facing the clinician is the management of critically ill patients in whom repeated attempts at weaning from mechanical ventilation are unsuccessful. The difficulty weaning these patients from the ventilator can be augmented in the presence of detraining of respiratory muscles, malnutrition, stress and the metabolic response to injury, and/or immobilization. An understanding of basic concepts of established tenets of exercise physiology and of nutritional support will allow their application to respiratory muscle function with the goal of facilitating the endurance and strength of respiratory muscles needed to sustain spontaneous ventilation.

The effect of the level of dietary protein, carbohydrate and fat on urea kinetics in young children during rapid catch-up weight gain

The kinetics of urea metabolism were measured in children recovering from severe malnutrition. For a period of up to 10 d they received one of four diets which provided 711 kJ (170 kcal)/kg per d. Two groups received a diet with a high protein:energy (P:E) ratio of 10-6% (HP), enriched with either fat (HP/F) or maize starch and sucrose (HP/C). Two groups received a diet with a low P:E ratio of 8.8% (LP), enriched with either fat (LP/F) or maize starch and sucrose (LP/C). The rate of weight gain on the HP diets was significantly greater than on the LP diets. There was no difference in urea production between any of the four diets: HP/F 1.23 (SE 0.12), HP/C 1.37 (SE 0.14), LP/F 1.64 (SE 0.22), LP/C 1.15 (SE 0.15) mmol nitrogen/kg per h. On the HP diets urea excretion was 0.77 (SE 0.07) mmol N/kg per h, 61% of production. There was significantly less urea excreted in the urine on diet LP/C than on LP/F (0.36 (SE 0.05) and 0.64 (SE 0.04) mmol N/kg per h respectively). A significantly greater percentage of the urea production was hydrolysed on the LP diets (61%) compared with the HP diets (39%), with the consequence that 50% of urea-N produced was available for synthetic activity on the LP diets compared with 30% on the HP diets. The increase in the urea hydrolysed on the LP diets was equivalent in magnitude to the decreased intake of N, so that overall intake plus hydrolysis did not differ between the LP and the HP diets. Crude N balance was similar on diets HP/F, HP/C and LP/C, but was significantly reduced on diet LP/F. These results show that there is an accommodation in urea kinetics during rapid catch-up weight gain, which becomes evident when the P:E ratio of the diet falls to 8.8%. It is proposed that, for a P:E ratio of 8.8%, protein is limiting for catch-up growth. When the intake has a P:E ratio of 8.8% the pattern of urea kinetics can be modified by the relative proportions of fat and carbohydrate in the diet. The measurement of urea kinetics provides a useful approach to the definition of the adequacy of the protein in the diet.

The physiology of nutritional assessment and therapy in protein-calorie malnutrition

Protein-calorie malnutrition (PCM), in the purest sense, is the result of depleted body protein stores due to semistarvation. A review of the hormonal response to simple semistarvation illustrates the elegant adaptive ability of the body to respond to an inadequate diet. By contrast, the body's metabolic response to an injury or illness stimulus is a dynamic process orchestrated by monokines and hormones. Although the injury response, strictly speaking, is not synonymous with PCM, the resultant increased energy expenditure, anorexia, and potential for skeletal muscle breakdown can result in an even more rapid depletion of body protein stores. Ultimately, the need for nutritional support depends on the amount of recent weight loss, anticipated time of insufficient oral intake, and the degree of stress. A discussion of basic concepts of anthropometry precedes examples of advantages and disadvantages of a given anthropometric parameter for selected disease states. The effects of PCM on visceral structure and function are discussed in detail so that the reader can appreciate why the metabolic response to injury may have a very different impact on the nourished compared with the malnourished patient. Particular attention is paid to the adverse effects of PCM on immune function and its antithesis, the beneficial impact of nutritional repletion on the immune system. An approach to refeeding discusses indications for initiation of nutritional support, choice of route, design of a macronutrient and micronutrient regimen, and guidelines for monitoring. Familiarity with the metabolic alterations of refeeding is key to the mitigation of potentially life-threatening complications of sudden refeeding. Appreciation of the anticipated response to nutrition is important, as the response will vary with the degree of stress. A nearly optimal response can be expected with appropriate nutrition in the nonstressed semistarved patient, whereas inefficient repletion is to be expected in the severely stressed patient. The review concludes with a discussion of the role of nutrition as a modifier of the body's metabolic response to injury.

Postoperative nutritional support of patients with abdominal trauma

The response to major trauma is characterized by a significant erosion of the body cell mass. Intensive nutritional support can decrease morbidity and mortality. Preservation and restoration of the body cell mass involves amino acid synthesis into protein, and this process requires nutrient energy. Newer methods of assessing energy expenditure have revised traditional concepts about energy requirements following trauma. The use of fat to meet some of the caloric requirements may obviate problems with ventilatory distress, glucose intolerance, and hepatic steatosis that occur with glucose-based nutritional regimens. Selection of the delivery method for intensive nutritional support should consider gastrointestinal integrity, physiologic tolerance, and cost. Enteral nutrition is superior to parenteral nutrition in maintaining gastrointestinal mucosal integrity, hormonal balance, and nutrient utilization. Furthermore, it is safer, more convenient, and more economical than parenteral nutrition.

Parenteral nutrition, and fluid and electrolyte therapy

The provision of fluid and electrolytes during parenteral nutrition can be a challenge in the malnourished child or the child with complicating illnesses. The practitioner using the basic concepts of maintenance and deficit therapy--in this case for calories--must adapt his or her therapy to the expansion of the intracellular as well as the extracellular fluid compartment. Impairment of other organ systems further complicates the ability to deliver therapy. Careful monitoring and individually tailored solution will provide adequate caloric fluid and electrolyte therapy during parenteral nutrition in children.

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.

Adjunctive therapy for nutritional support in hospitalized patients

It would be unrealistic to expect that a single adjuvant modality may be applicable to all patients receiving nutritional support, either IV or enterally. Further characterization of the optimal application of each adjuvant modality may establish the precise role of adjuvant anabolic stimulation throughout the clinical course. Better definition of IV formulas with addition of stable glutamine dipeptides may be of benefit in patients at high risk for sepsis and significant skeletal muscle wasting, while use of met-hGH may improve nitrogen retention and whole-body net protein accrual under these circumstances. Chronic, low- to moderate-intensity exercise may be applicable in a select group of patients, particularly patients at risk for developing complications after surgical intervention in whom aggressive nutritional support has been shown to improve operative outcome.

Nutrient interactions with total parenteral nutrition: effect of histidine and cysteine intake on urinary zinc excretion

Because cysteine and histidine, two amino acids included in total parenteral nutrition regimens, bind zinc and increase its renal ultrafilterability, my objective was to quantify the effects of infusion of amino acids, including cysteine and histidine, on urinary zinc excretion. The effect of the infusion of high amounts of cysteine and no cysteine (100 mg/kg/day vs none) and of high and low amounts of histidine (165 vs. 95 mg/kg/day) on urinary zinc excretion was determined in 14 newborn infants receiving total parenteral nutrition who had similar zinc intakes (approximately 7 mumol/kg/day). After a 72-hour adaptation period, each infant's urine was collected for two 48-hour periods. Urinary zinc excretion during the high-dose histidine and cysteine infusion periods was significantly elevated compared with that during the no-cysteine and low-dose histidine periods. Therefore concurrent intakes of specific amino acids may have to be considered when zinc dosages are calculated.

Rate of weight loss during underfeeding: relation to level of physical activity

The kinetics and bioenergetic-metabolic determinants of weight loss were examined in obese women ingesting 900 kcal/d for 5 weeks. The patients were assigned either to a sedentary group (n = 5) or to an exercise group (n = 6) in which the participants expended an additional (X +/- SD) 346 +/- 61 kcal/d in aerobic physical activity. The percentage weight loss and the fractional rates (K1 = fast component; K2 = slow component) of weight loss were almost identical between the two groups. The failure of added exercise to increase the velocity of weight loss could not be explained by differences between the groups in any of the following: gastrointestinal energy and nitrogen (N) absorption; fractional rates of urinary urea N and total N loss; or the thermic effect of the formula diet. The cumulative and fractional rates of protein (ie N) loss were also similar between the groups. The exercise group lost more fat (5.3 +/- 1.0 kg) than the non-exercise group (4.4 +/- 1.6 kg, P less than .001) as measured by underwater weighing. The maximum between-group difference in the rate of fat loss, as determined by energy-N balance, occurred during early underfeeding. With continuation of the 900 kcal/d diet, the between-group differences in the rate of fat loss diminished. The exercise subjects significantly lowered their resting heat losses relative to the non-exercise subjects (P less than .025). This in turn reduced the degree of negative energy balance in the more energy-deficient exercise group.(ABSTRACT TRUNCATED AT 250 WORDS)

Ethanol: relative fuel value and metabolic effects in vivo

A nasogastric formula infusion method was used to evaluate the steady-state fuel value of ethanol relative to that of glucose in eight chronically alcoholic men undergoing a 4- or 5-week balance experiment. Each subject received a maintenance infusion of the formula diet throughout the study. When control formula glucose (week 1) was isocalorically replaced with ethanol [week 2, 30% of kcal; week 3 or 4 (5-week experiment) 40% to 60% of kcal], the following was observed: weight loss; zero energy balance and reduced or negative balances of N, K, P, Mg, and Na; increased urinary urea N and 3-methylhistidine; lowered urinary C-peptide; no change in indirectly or directly measured thermal energy losses; and a blood level related rise in breath and urinary ethanol losses. All of these changes promptly reversed during the middle (week 3 in 5-week experiment) and final control weeks. Accounting for all diet-related energy losses (urine, breath, thermal), the fuel value of the ethanol-containing diet relative to the glucose control formula varied between 0.95 and 0.99, depending upon the blood alcohol level. Hence weight loss during short-term (seven-day) ethanol infusion is unrelated to overall negative energy balance, stems primarily from decrements in protein, minerals, and fluid, and may in part be mediated by the reduction in insulin secretion that accompanies switching from dietary glucose to ethanol.

Effect of starvation and total parenteral nutrition on electrolyte homeostasis in normal man

Elemental balances, and skeletal muscle membrane potential (Em) and biopsy were utilized to evaluate electrolyte homeostasis and body composition in 11 healthy adult volunteers after 10 days of starvation. This controlled, acute malnutrition was followed by refeeding for 10 days with two different, commonly used, total parenteral nutrition (TPN) solutions. Six subjects were refed with crystalline amino acids and dextrose (dextrose group), while five subjects received amino acids, dextrose, and lipid (lipid group). During starvation, negative balances for potassium, phosphorous, magnesium, and nitrogen were observed in both groups. When compared to starvation, total parenteral nutrition produced statistically significant (p less than 0.05) equilibrium or positive electrolyte and nitrogen balances for both, the dextrose and lipid groups. During TPN, there was a significantly (p less than 0.001) positive chloride balance in the lipid group when compared to the dextrose group. At the conclusion of the 10-day period of TPN, there was a decrease (p less than 0.05) in skeletal muscle Em. This change, in concert with the electrolyte balance data obtained during parenteral repletion, lead us to postulate that restoration of lean tissue protein and cellular function does not occur at a rate which might be inferred from the positive nitrogen balance observed in this model. A persistent defect in cellular function which was evident after starvation, suggests that a brief period of TPN is insufficient to restore skeletal muscle integrity.

Free amino acid formula: nitrogen utilization and metabolic effects in normal subjects

A previous study indicated increased urea production and low nitrogen (N) retention on a free amino acid elemental formula (FAA; Vivonex-HN). The limitations of this earlier study were: irregular nitrogen absorption in the malabsorption patients, high nitrogen intake, and failure to match FAA to control formula (hydrolyzed casein; CAS; Criticare-HN) with respect to kcal/nitrogen. A more critical test of FAA quality was sought in the current study. Four healthy males received the minimal daily nitrogen requirements (0.6 g protein/kg) from either FAA or CAS in a 10-day balance study; a second balance on the alternate formula followed. Maintenance energy, minerals, and vitamins were supplied in each period. The results indicated a higher apparent nitrogen absorption (p less than 0.05) from FAA relative to CAS in the first 5 days of the balance, although these differences were no longer present in the remaining 5 days of the period. Urinary total nitrogen increased on FAA, most of which could be accounted for by urea nitrogen; urinary creatinine nitrogen, ammonia nitrogen, and uric acid nitrogen were nearly identical between formulas. The unmeasured fraction of urinary nitrogen was markedly diminished on FAA while the urea nitrogen to total nitrogen ratio was significantly increased (p less than 0.05) compared to CAS. During the initial 5 days of study nitrogen balance was lower on FAA than on CAS and this difference became significant during the last 5 days of the period (mean +/- SD for FAA = -0.42 +/- 0.59 g/D vs CAS = 0.98 +/- 0.30 g/day, p less than 0.001). Hyperglycinemia was consistently present during FAA infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Uses and limitations of the balance technique

Classical balance techniques are a powerful, sensitive, and usually accurate technique for assessing the nutritional or metabolic response to changes in nutritional intake or to metabolic or physiological perturbations. Balances are particularly sensitive for examining transient or short-term responses to nutritional or metabolic stimuli. A major factor responsible for the precision and sensitivity of this technique is the precise control of the activities and environment of an individual during a classical metabolic balance study (eg, the carefully defined dietary intake, degree of exercise, and environmental temperature to prevent sweating); these same factors may enhance the precision and sensitivity of other metabolic or nutritional investigations that may be carried out concurrently with a balance study. Finally, for nitrogen balance studies, the measurement of nitrogen (eg, by the Kjeldahl technique) can be very accurate and sensitive. Despite these advantages, there are important limitations and errors that are inherent in the balance technique. The errors tend to overestimate intake and underestimate output, thereby leading to erroneously positive balances. These errors include losses of food on cooking and eating utensils and dishware, losses of feces or urine on toilet paper or in collection containers, and losses through sweat, exfoliated skin, hair and nail growth, saliva, menses, blood sampling, toothbrushing, semen, and, for nitrogen, from flatus and respiration. Cumulative balance measurements are particularly likely to be falsely positive. The magnitude of unmeasured losses vary among healthy individuals, with the magnitude of the nitrogen intake (for nitrogen), in altered environmental conditions (eg, with sweating), and possibly in disease states. Balance studies are also expensive and time consuming.(ABSTRACT TRUNCATED AT 250 WORDS)

Bioenergetic and metabolic response to continuous v intermittent nasoenteric feeding

Resting thermal energy losses and metabolic balances of N, K, P, Ca, Na, and Mg were compared during continuous and intermittent nasoenteric formula infusion in four healthy men. Each feeding protocol lasted 1 week in a 4-week double crossover experiment. The initial feeding schedule was established randomly. Continuous nasoenteric formula infusion produced no increase in thermal energy losses above the fasting level; energy expenditure fell with sleep to the same extent as with intermittent feeding. Thermal losses were similar during intermittent feeding with the exception of the thermic effect of food that produced an additional average energy loss of 115.7 kcal/d. The total resting and sleeping 24-hour energy expenditure was significantly lower (P less than .01) during continuous formula infusion (means +/- SD for n = 8 balance periods, 1344 +/- 119 kcal) compared to intermittent feeding (1457 +/- 179 kcal). No significant differences in nutrient absorption or balances of N, Na, Ca, and Mg were detected between the two feeding protocols. In contrast, continuous infusion of formula was accompanied by negative balances of K and the cytosolic portion of P; weight balance was slightly negative. Weight, K, and cytosolic P balances were all positive during intermittent feeding (P = NS, less than 0.01, and P less than .05 compared to respective continuous infusion periods). Hence, 1 week of continuous nasogastric formula infusion is associated with similar nutrient absorption, a significant reduction in thermal energy losses, and equivalent protein (N) balance relative to intermittent feeding. Differences in weight balance between the two feeding protocols can be ascribed largely to fluid and mineral shifts. These results suggest that energy requirements are lower during continuous formula infusion by about 100 kcal/d compared to regular meal ingestion.

Potassium homeostasis and hypokalemia

Potassium, largely an intracellular cation, contributes to the regulation of cellular volume, to tissue growth and metabolic synthesis of proteins and nucleic acids, and to the integrity of electrical properties of excitable tissues as well as nonexcitable, transporting epithelia. Potassium balance is closely regulated by a variety of nonrenal and renal mechanisms. When potassium losses are sufficient to induce hypokalemia, either through nonrenal or renal causes, profound adverse effects on neuromuscular, cardiac, vascular, and renal tissues may ensue. The diagnostic approach is straightforward, and therapy must be directed to replenish losses without inducing a rapid, excessive, and potentially fatal increase in the potassium concentration of the serum.

Value of nutritional support in adult cancer patients

Both the presence of cancer and oncologic therapy cause metabolic alterations that may decrease the ability of the host to maintain anabolism. Nutritional support, properly administered, will replenish lean body mass, visceral proteins, and immunocompetence in human beings and experimental animals with small to modest tumor burdens. To date, stimulation of tumor growth by intravenous hyperalimentation in malnourished patients has not been documented scientifically. The exact role of intravenous hyperalimentation, in combination with chemotherapy or radiation therapy, is controversial, whereas the role of nutritional support for the malnourished surgical patient is more firmly established.

Protein metabolism in inflammatory bowel disease

Major loss of body protein mass in inflammatory bowel disease is much less common than weight loss, which is often attributable to losses of other body, particularly water and fat. It does occur, however, in a few patients, especially in those with compromised food intake. It is due principally to the combined effects of diminished intake and excessive intestinal losses of amino nitrogen. Nitrogen metabolism is influenced not only by protein nutritional state and net nitrogen intake but also by disease activity. There is some evidence for abnormally low secretion of growth hormone in adolescents with inflammatory bowel disease and growth failure. Low serum albumin concentrations are not necessarily related to protein undernutrition and are the combined result of relatively reduced albumin synthesis, increased intestinal losses, and maldistribution between intravascular and extravascular spaces. Concentrations in the plasma of IgG and acute phase reactants may be raised despite increased losses into the bowel lumen. The prevention of total body protein depletion is achieved principally by maintaining adequate and often not supranormal intakes of a balanced source of amino nitrogen in a balanced diet given orally, enterally, or parenterally, combined with a medical or surgical approach to reduce disease activity: supranormal energy intakes are not beneficial.

Extremity amino acid metabolism during starvation and intravenous refeeding in humans

This study was designed to evaluate peripheral tissue amino acid metabolism in normal subjects who underwent starvation followed by intravenous administration of a nutritional repletion regimen with varying nonprotein caloric sources. Extremity amino acid (AA), arteriovenous differences, and blood flow were measured across forearm and/or leg of 12 healthy male subjects. Plasma AA flux [(arterial concentration - venous concentration) X flow X (1 - hematocrit); ml X min-1 X 100 ml tissue-1] was determined postabsorptively (PA), after 10 days of starvation (ST) and on the 10th day of intravenous feeding (IVF). There was a significant (P less than 0.05) decrease in efflux of total amino acids during the starvation study (-345 +/- 74) compared with the PA study (-1,463 +/- 263). Peripheral tissue AA uptake increased significantly (P less than 0.05) after 10 days of IVF (+276 +/- 79) compared with both PA and ST studies. There were no significant differences in extremity AA flux between those subjects who received 100% dextrose and those receiving 50% dextrose-50% lipid as a nonprotein caloric source. Linear relationships of AA infusion rate (IR) to AA flux (r = 0.845, P less than 0.001) and AA IR to [AA]art IVF (r = 0.842, p less than 0.001) were observed during IVF. Results of this study suggest that extremity flux determinations during IVF cannot be interpreted without correction for AA availability as reflected by AA infusion rate.

Main nitrogen balance determinants in malnourished patients

Factors influencing nitrogen balance during total parenteral nutrition have been investigated in 38 malnourished patients studied for a cumulative period of 280 days. According to multiple regression analysis, nitrogen intake (0.213 +/- 0.004 g kg-1 day-1, mean +/- SD) proved to be the major determinant of a positive nitrogen balance (0.018 +/- 0.004 g kg-1 day-1), followed by non-protein energy intake (43.3 +/- 0.5 kcal kg-1 day-1). Total calorie intake to predicted basal energy expenditure and non protein calorie to nitrogen ratios appeared to have little significance on nitrogen balance, when corrected for the two former variables.

Effects of varying protein and energy intakes on growth and metabolic response in low birth weight infants

Growth (weight, length, head circumference, and skinfold thickness), retention of major nutrients (nitrogen, sodium, potassium, chloride, calcium, and phosphorus), and chemical indices of protein adequacy (plasma albumin and transthyretin concentrations) and excess (blood urea nitrogen concentration and acid-base status; plasma amino acid concentrations) were determined serially from the time desired intake was tolerated until discharge weight (2200 gm) was reached in low birth weight infants (birth weight 900 to 1750 gm) fed one of three formulas, which provided protein and energy intakes, respectively, of 2.24 gm/kg/day and 115 kcal/kg/day (group 1), 3.6 gm/kg/day and 115 kcal/kg/day (group 2), and 3.5 gm/kg/day and 149 kcal/kg/day (group 3). Weight gain and rate of increase in length and head circumference were less in group 1 than in groups 2 and 3. Retention of most major nutrients also was less in group 1, as was blood urea nitrogen concentration, plasma albumin and transthyretin concentrations, and plasma concentrations of several amino acids. The rate of weight gain was not significantly greater in group 3 than in group 2, but the rate of increase in skinfold thickness was greater in this group. Neither nutrient retention nor metabolic indices differed between groups 2 and 3. These results suggest that a protein intake of 2.24 gm/kg/day is inadequate for the type of LBW infants studied, that the higher protein intakes are well tolerated, and that an energy intake of 149 vs 115 kcal/kg/day does not enhance utilization of the higher protein intakes studied.

Effect of total parenteral nutrition on the zinc, copper, and manganese status of patients with catabolic disease

The zinc, copper, and manganese concentrations in liver and muscle and the serum zinc were measured in 24 malnourished patients before and after 10-12 days' parenteral nutrition with 3 different alimentation programs. The nutrition programs contained similar trace element substitutions. Malnutrition caused by different catabolic diseases resulted in an increase of zinc and copper contents in the liver and a rise of serum zinc in many patients and in a decrease of muscle zinc concentration in certain patients. Parenteral nutrition of any kind resulted in a decrease of liver zinc and copper content and of serum zinc, yielding subnormal zinc values in 25-58% of the patients in spite of a daily substitution of 1.9 mg zinc. There was no significant change in the manganese status because of malnutrition or parenteral alimentation. It is concluded that the serum zinc concentration does not show the real zinc status of the body in the patients with catabolism, that in certain catabolic diseases zinc and copper are redistributed to the liver, that certain catabolic diseases cause a zinc depletion of the muscle, that parenteral nutrition results in a fall of zinc and copper in the liver and in a decrease of serum zinc, which may be harmful from the healing point of view, and that the daily substitution of zinc used in this study, 1.9 mg/day, is not sufficient during parenteral nutrition of catabolic patients.

Reduction of total parenteral nutrition-induced urinary calcium loss by increasing the phosphorus in the total parenteral nutrition prescription

Hypercalciuria and negative calcium balance are potential complications of total parenteral nutrition (TPN). Dietary phosphorus has been observed to have an hypocalciuretic effect. The present study evaluates the effects of administration of increasing intravenous phosphorus (P) loads on urinary calcium excretion in TPN patients. Urinary calcium exceeded daily calcium intake by 50 mg/d when 700 mg/d P was administered, was equal to intake at 1000 mg/d P, and was 30 mg/d less than calcium intake when 1300 mg/d P was given. These findings suggest that TPN-induced hypercalciuria can be attenuated in the short-term by intravenous phosphate. Reevaluation of the phosphorus requirement in patients receiving long-term TPN should be considered.

Tube feeding of cancer patients treated with chemotherapy

As many chemotherapeutic agents affect the alimentary tract the use of hyperalimentation with tube feeding during and after chemotherapy has been limited. However, patients do tolerate tube feeding well despite chemotherapy. The feeding has to be administered as continuous drip infusion and in case of bone marrow depression sterile feeding is necessary. Enteral nutrition is more physiologic, safer, easier and less expensive than parenteral nutrition. With enteral hyperalimentation the nutritional needs can be fulfilled to a large extent. Much research will be necessary to investigate the effect of enteral (hyper)alimentation on tumor metabolism and clinical effect of chemotherapy.

Estimating the composition of tissue gained or lost from measurements of elementary body composition

Studies of relationships between changes in body constituents resulting from disease or treatment can, in principle, give information about the composition of the tissues gained or lost. Frequently, however, the random errors of measurement are of similar magnitude to the changes measured, so that standard statistical methods such as linear regression analysis give biased estimates of the parameters in the relationships. Possible ways of obtaining better estimates are discussed and models suitable for two types of experiment are described. In the first, patients are measured before and after the changes; in the second, patients are measured only after the changes have occurred and their results compared with those for a group of control subjects assumed to be representative of the patients before they became ill. The models have been used to analyse losses of total body nitrogen and potassium as a result of surgery and of disease. The results suggest that patients who underwent surgical operation lost 1.7 mmol K per g N. Those who suffered from disease lost 2.0 mmol K per g N, but also lost, on average, 234 mmol K independently of N. Conventional linear regression analysis would have led to very different conclusions, emphasising the importance of applying appropriate models to the analysis of such data.