Partition of energy metabolism in the surgical newborn

Personalized metabolic whole-body models for newborns and infants predict growth and biomarkers of inherited metabolic diseases

Comprehensive whole-body models (WBMs) accounting for organ-specific dynamics have been developed to simulate adult metabolism, but such models do not exist for infants. Here, we present a resource of 360 organ-resolved, sex-specific models of newborn and infant metabolism (infant-WBMs) spanning the first 180 days of life. These infant-WBMs were parameterized to represent the distinct metabolic characteristics of newborns and infants, including nutrition, energy requirements, and thermoregulation. We demonstrate that the predicted infant growth was consistent with the recommendation by the World Health Organization. We assessed the infant-WBMs' reliability and capabilities for personalization by simulating 10,000 newborns based on their blood metabolome and birth weight. Furthermore, the infant-WBMs accurately predicted changes in known biomarkers over time and metabolic responses to treatment strategies for inherited metabolic diseases. The infant-WBM resource holds promise for personalized medicine, as the infant-WBMs could be a first step to digital metabolic twins for newborn and infant metabolism.

Evolution of Resting Energy Expenditure, Respiratory Quotient, and Adiposity in Infants Recovering from Corrective Surgery of Major Congenital Gastrointestinal Tract Anomalies: A Cohort Study

This cohort study describes the evolution of resting energy expenditure (REE), respiratory quotient (RQ), and adiposity in infants recovering from corrective surgery of major congenital gastrointestinal tract anomalies. Energy and macronutrient intakes were assessed. The REE and RQ were assessed by indirect calorimetry, and fat mass index (FMI) was assessed by air displacement plethysmography. Longitudinal variations over time are described. Explanatory models for REE, RQ, and adiposity were obtained by multiple linear regression analysis. Twenty-nine infants were included, 15 born preterm and 14 at term, with median gestational age of 35.3 and 38.1 weeks and birth weight of 2304 g and 2935 g, respectively. In preterm infants, median REE varied between 55.7 and 67.4 Kcal/kg/d and median RQ increased from 0.70 to 0.86–0.92. In term infants, median REE varied between 57.3 and 67.9 Kcal/kg/d and median RQ increased from 0.63 to 0.84–0.88. Weight gain velocity was slower in term than preterm infants. FMI, assessed in a subset of 15 infants, varied between a median of 1.7 and 1.8 kg/m² at term age. This low adiposity may be related to poor energy balance, low fat intakes, and low RQ¸ that were frequently recorded in several follow-up periods.

Predicting growth of the healthy infant using a genome scale metabolic model

An estimated 165 million children globally have stunted growth, and extensive growth data are available. Genome scale metabolic models allow the simulation of molecular flux over each metabolic enzyme, and are well adapted to analyze biological systems. We used a human genome scale metabolic model to simulate the mechanisms of growth and integrate data about breast-milk intake and composition with the infant's biomass and energy expenditure of major organs. The model predicted daily metabolic fluxes from birth to age 6 months, and accurately reproduced standard growth curves and changes in body composition. The model corroborates the finding that essential amino and fatty acids do not limit growth, but that energy is the main growth limiting factor. Disruptions to the supply and demand of energy markedly affected the predicted growth, indicating that elevated energy expenditure may be detrimental. The model was used to simulate the metabolic effect of mineral deficiencies, and showed the greatest growth reduction for deficiencies in copper, iron, and magnesium ions which affect energy production through oxidative phosphorylation. The model and simulation method were integrated to a platform and shared with the research community. The growth model constitutes another step towards the complete representation of human metabolism, and may further help improve the understanding of the mechanisms underlying stunting.

Is Energy Expenditure of Infants Predictable After Surgery?

Infants undergoing surgery have unique metabolic demands. The stress of an operation and recovery combined with expectations for growth and development imply elevations in energy expenditure beyond that of healthy, free-living infants. In contrast, surgery may trigger a diversion of energy utilization from tissue accumulation and growth toward the catabolic stress response and cytokine production. Predictive equations are commonly used in clinical settings to estimate basal or resting energy expenditure because measurement techniques such as indirect calorimetry may not be feasible or available. Investigations of measured energy expenditure in surgical infants have portrayed mixed results, however, and estimation equations may not consistently lead to accurate assessment of actual energy needs. Studies are limited in number and quality and often involve a heterogeneous, small population. Grouped outcomes may conceal the wide variability frequently observed in these studies. Measurement of energy expenditure is therefore preferable to the use of predictive equations to customize nutrition intervention for individual infants undergoing surgery.

Metabolism and nutrition in the surgical neonate

Considerable improvements have been achieved in pediatric surgery during the last two decades: the mortality rate of neonates undergoing major operations has declined to less than 10%, and the morbidity of major operations has become negligible. This considerable improvement can be partly ascribed to a better understanding of the physiological changes that occur after an operation and to more appropriate management and nutrition of the critically ill and "stressed" neonates and children. The metabolic response to an operation is different in neonates from adults: there is a small increase in oxygen consumption and resting energy expenditure immediately after surgery with return to normal by 12-24 hours. The increase in resting energy expenditure is significantly greater in infants having a major operation than in those having a minor procedure. The limited increase in energy expenditure may be due to diversion of energy from growth to tissue repair. During parenteral nutrition, it is not advisable to administer more than 18 g/kg/day of carbohydrate because this intake will be associated with lipogenesis, increased CO(2) production, and increased free radical-mediated lipid peroxide formation. Glutamine intake is potentially beneficial during total parenteral nutrition, although a large, randomized, controlled trial in surgical neonates requiring parenteral nutrition is needed to provide evidence for its benefit.

Energy expenditure and caloric and protein intake in infants following the Norwood procedure

OBJECTIVES

Cardiopulmonary bypass in infants results in a hypermetabolic response. Energy requirements of these patients have not been well studied. We assessed energy expenditure and caloric and protein intake during the first 3 days following the Norwood procedure.

DESIGN

Clinical investigation.

SETTING

Children's hospital.

PATIENTS

Seventeen infants (15 boys, age 4-92 days, median 7 days).

INTERVENTIONS

VO2 and VCO2 were continuously measured using respiratory mass spectrometry in 17 infants for the first 72 hrs following the Norwood procedure. The respiratory quotient was determined as VCO2/VO2. Energy expenditure was calculated using the modified Weir equation. Measurements were collected at 2- to 4-hr intervals. The mean values in the first 8 hrs, hours 8-32, hours 32-56, and the last 16 hrs were used as representative values for postoperative days 0, 1, 2, and 3. Total caloric and protein intakes were recorded for each day.

MEASUREMENTS AND MAIN RESULTS

Energy expenditure, VO2, and VCO2 were initially high; declined rapidly during the first 8 hrs; and were maintained relatively stable in the following hours (p < .0001). Respiratory quotient showed a significant linear increase over the 72 hrs (p = .002). Energy expenditure on days 0, 1, 2, and 3 was 43 +/- 11, 39 +/- 8, 39 +/- 8, and 41 +/- 6 kcal/kg/day, respectively. Total caloric intake was 3 +/- 1, 14 +/- 5, 31 +/- 16, and 51 +/- 16 kcal/kg/day. Protein intake was 0, 0.2 +/- 0.2, 0.6 +/- 0.5, and 0.9 +/- 0.5 g/kg/day on days 0, 1, 2, and 3, respectively.

CONCLUSIONS

Infants exhibit a hypermetabolic response immediately following the Norwood procedure. Caloric and protein intake was inadequate to meet energy expenditure during the first 2 days after surgery. Further studies are warranted to examine the effects of caloric and protein supplementation on postoperative outcomes in infants after cardiopulmonary bypass.

Glutamine supplementation of parenteral nutrition does not improve intestinal permeability, nitrogen balance, or outcome in newborns and infants undergoing digestive-tract surgery: results from a double-blind, randomized, controlled trial

OBJECTIVE

To assess the effect of isocaloric isonitrogenous parenteral glutamine supplementation on intestinal permeability and nitrogen loss in newborns and infants after major digestive-tract surgery.

SUMMARY BACKGROUND DATA

Glutamine supplementation in critically ill and surgical adults may normalize intestinal permeability, attenuate nitrogen loss, improve survival, and lower the incidence of nosocomial infections. Previous studies in critically ill children were limited to very-low-birthweight infants and had equivocal results.

METHODS

Eighty newborns and infants were included in a double-blind, randomized trial comparing standard parenteral nutrition (sPN; n = 39) to glutamine-supplemented parenteral nutrition (GlnPN; glutamine target intake, 0.4 g kg day; n = 41), starting on day 2 after major digestive-tract surgery. Primary endpoints were intestinal permeability, as assessed by the urinary excretion ratio of lactulose and rhamnose (weeks 1 through 4); nitrogen balance (days 4 through 6), and urinary 3-methylhistidine excretion (day 5). Secondary endpoints were mortality, length of stay in the ICU and the hospital, number of septic episodes, and usage of antibiotics and ICU resources.

RESULTS

Glutamine intake plateaued at 90% of the target on day 4. No differences were found between patients assigned sPN and patients assigned GlnPN regarding any of the endpoints. Glutamine supplementation was not associated with adverse effects.

CONCLUSIONS

In newborns and infants after major digestive-tract surgery, we did not identify beneficial effects of isonitrogenous, isocaloric glutamine supplementation of parenteral nutrition. Glutamine supplementation in these patients therefore is not warranted until further research proves otherwise.

Normal value of resting energy expenditure in healthy neonates

OBJECTIVE

We investigated the value of resting energy expenditure (REE) in healthy neonates and evaluated the impact factors on REE.

METHODS

One hundred eighty healthy neonates (95 boys and 85 girls) with birth weights above 2500 g were measured by indirect calorimetry, and the effect of birth weight evaluated. Measured and predicted REEs were compared, and the effects of sex and delivery method on REE were examined in 154 newborn infants with birth weights of approximately 2500 to 4000 g.

RESULTS

Birth weight had a significant effect on REE. There was a negative relation between REE and birth weight (r = -0.289). The REEs of newborn infants weighing more than 4000 g were statistically lower than those of infants weighing 2500 to 4000 g (44.5 +/- 5.9 versus 48.3 +/- 6.1 kcal x kg(-1) x d(-1), P = 0.01). The measured and predicted REEs of 154 newborn infants were 48.3 +/- 6.1 and 54.1 +/- 1.1 kcal x kg(-1) x d(-1), respectively. There was a significant difference between the two values. Sex and delivery methods had no effect on REE in healthy neonates.

CONCLUSIONS

The value from the predicted equation is not suitable for neonatal energy supplementation in clinical practice. The normal REE value for healthy neonates with birth weights of 2500 to 4000 g is 48.3 +/- 6.1 kcal x kg(-1) x d(-1).

Nutrition for the pediatric surgical patient: approach in the peri-operative period

Nutrition is essential for maintenance of physiologic homeostasis and growth. Hypermetabolic states lead to a depletion of body stores, with decreased immunocompetence and increased morbidity and mortality. The purpose of this paper is to provide an update regarding the provision of appropriate nutrition for the pediatric surgical patient, emphasizing the preoperative and postoperative periods. Modern nutritional support for the surgical patient comprises numerous stages, including assessment of nutritional status, nutritional requirements, and nutritional therapy. Nutritional assessment is performed utilizing the clinical history, clinical examination, anthropometry, and biochemical evaluation. Anthropometric parameters include body weight, height, arm and head circumference, and skinfold thickness measurements. The biochemical evaluation is conducted using determinations of plasma levels of proteins, including album, pre-albumin, transferrin, and retinol-binding protein. These parameters are subject to error and are influenced by the rapid changes in body composition in the peri-operative period. Nutritional therapy includes enteral and/or parenteral nutrition. Enteral feeding is the first choice for nutritional therapy. If enteral feeding is not indicated, parenteral nutrition must be utilized. In all cases, an individualized, adequate diet (enteral formula or parenteral solution) is obligatory to decrease the occurrence of overfeeding and its undesirable consequences.

The metabolic response to intravenous medium-chain triglycerides in infants after surgery

OBJECTIVE

The aim of this study was to determine if administration of mixed medium-chain triglycerides (MCT)/long chain triglycerides (LCT) fat emulsion would increase net fat oxidation and if carbohydrate intake would influence net fat oxidation.

STUDY DESIGN

Stable infants receiving total parenteral nutrition were studied after surgery. Respiratory gas exchange was measured by indirect calorimetry and urinary nitrogen excretion by the micro-Kjeldahl method. Intravenous fat (4 g/kg/day) was given as either pure LCT fat emulsion or 50/50 MCT/LCT fat emulsion. Carbohydrate intake was either "high" (15 g/kg/day) or "low" (10 g/kg/day). Four groups of patients were studied: group 1 = LCT and high-carbohydrate; group 2 = LCT and low-carbohydrate; group 3 = MCT/LCT and high-carbohydrate; group 4 = MCT/LCT and low-carbohydrate.

RESULTS

At a carbohydrate intake of 15 g/kg/day, the calories available from glucose exceeded the measured resting energy expenditure (REE), and no differences were seen in either energy expenditure or net fat oxidation between patients receiving LCT and MCT/LCT fat emulsions. However, at a carbohydrate intake of 10 g/kg/day, when glucose calories were less than REE, net fat oxidation was significantly higher in patients receiving MCT/LCT (median, 1.94; range, 1.05-2.24 g/kg/day) compared with patients receiving LCT (median, 0.60; range, -0.09 to 1.35; P =.03).

CONCLUSION

Providing that carbohydrate calories do not exceed REE, partial replacement of LCT by MCT in intravenous fat emulsions can increase net fat oxidation in infants after surgery.

Nutritional support of the critically ill child

The pediatric metabolic response to injury and operation is proportional to the degree of stress and causes an increase in the turnover of proteins, fats, and carbohydrates. Thereby, substrates are made readily available for the immune response and wound healing. Because this process requires energy, the resting energy expenditure of ill patients increases. Whole-body protein degradation rates are elevated out of proportion to synthetic rates, and negative protein balance also ensues. Neonates and children are particularly susceptible to the loss of lean body mass and its attendant increased morbidity and mortality caused by an intrinsic lack of endogenous stores and greater baseline requirements. An appropriately designed mixed fuel system of nutritional support replete in protein does not quell this metabolic response but can result in anabolism and continued growth in ill children. In addition, the use of adequate analgesia and anesthesia is a readily available and proven means of reducing the magnitude of the catabolism associated with operation and injury. Finally, as hormonal- and cytokine-mediated metabolic alterations are better understood, therapeutic interventions may become available to directly modulate the metabolic response to illness, thus potentially further improving clinical outcome in pediatric surgical patients.

Metabolism and nutritional support in the surgical neonate

Various factors can influence the metabolism of surgical neonates. These include prematurity, operative stress, critical illness, and sepsis. The nutritional management of surgical infants with congenital or acquired intestinal abnormalities has improved after the introduction of parenteral nutrition. This article is focused on the energy and protein metabolism of surgical neonates with particular reference to the metabolic response to operative trauma and sepsis. The metabolic utilization of intravenous nutrients also is discussed. The metabolic response to operative trauma is different between neonates and adults. Infants have high rates of protein turnover and are avid retainers of nitrogen. Energy expenditure increases only transiently (4 to 6 hours) after major surgery in neonates. Protein turnover and catabolism seems not to be affected by major operative procedures in neonates. In neonates on parenteral nutrition, carbohydrate and fat have an equivalent effect on protein metabolism. The main determinants of fat utilization are carbohydrate intake and resting energy expenditure. Parenteral nutrition in surgical neonates is associated with increased production of oxygen-free radicals. This seems to be related to intravenous fat administration. Promoting fat utilization by reducing the carbohydrate to fat ratio in the intravenous diet reduces free radical activity to a similar extent as fat exclusion. Glutamine appears to be safe for use in neonates and infants and is "conditionally essential" in very-low birth weight infants and in septic neonates. Enteral glutamine supplementation in very-low birth weight infants reduces the risk of sepsis. The metabolism of surgical neonates is affected by operative trauma, critical illness, and sepsis. Nutritional support in surgical neonates has a profound impact on outcome. Exogenous glutamine can modulate immune, metabolic, and inflammatory responses. Further investigations are needed to clarify the clinical benefit of parenteral or enteral glutamine administration in surgical neonates.

Early postoperative feeding and outcome in neonates

OBJECTIVES

The results of neonatal surgery in the Western world have rapidly improved over the past three decades. Early nutrition support is thought to be one of the key factors. We used transgastric, transanastomotic feeding jejunostomy tubes in every infant undergoing upper gastrointestinal surgery when the expected period of fasting has exceeded 7 d.

METHODS

Newborns with duodenal atresia, malrotation, and jejunal atresia were treated consecutively between November 1998 and November 1999. We analyzed the outcome of such a practice. There were 17 consecutive babies recruited into the study. Ten babies had duodenal atresia, one associated with esophageal atresia and tracheo-esophageal fistula, six had malrotation, and one had jejunal atresia. The weights of the babies varied between 1.2 and 3.78 kg (mean = 2.1 kg) and they were referred between the ages of 1 and 23 d. Three babies were younger than 32 wk of gestation and weighed less than 1.5 kg; all had multiple bowel atresia, including one with associated pyloric atresia. None of these three survived. Enteral feeding was started by postoperative day 2 in 14 cases. Period of feeding varied between 3 and 20 d, with a mean of 10.4 d in the surviving babies. Three of the tubes had minor mechanical complications.

RESULTS

The weight loss or gain during the period of hospitalization was not significant (P = 0.3) Breast milk was the most common nutrient. Thirteen of the 14 babies weighing more than 1.5 kg were discharged and are being followed; the remaining baby died from neonatal septicemia. Excellent results can be obtained with aggressive enteral nutrition support in newborns undergoing upper intestinal surgery.

CONCLUSIONS

Transgastric, transanastomotic feeding jejunostomy was well tolerated by the newborns and is preferable to parenteral nutrition.

Nutrition support in a surgical patient

Nutrition has very important role to play during health and disease state in human beings. Neonates and younger children are more prone to develop nutritional deficiencies. They have very critical reserves and are rapidly growing. Any surgical insult leads to multiple nutritional problems. Careful planning of nutritional management in a surgical patient is mandatory. Nutritional support should start from the day when the child develops the surgical condition to withstand stress of disease and surgical procedure. In the postoperative period nutritional support should start as early as possible. Start with small amount and build up gradually till the normal enteral nutrition (EN) is tolerated. When EN is not tolerated parenteral nutrition (PN) should be considered. Parenteral nutrition on short term basis is very important to tide over the crisis due to postoperative complications. Parenteral nutrition on long term basis is required in short bowel syndrome resulting from resection of large part of the gut. During PN, enteral nutrition should be continued in small amounts in order to maintain the integrity of mucosal lining of the gut. Enteral nutrition is more physiological and can provide adequate amount of immunonutrients, minerals and vitamins.

Energy metabolism of infants and children with systemic inflammatory response syndrome and sepsis

OBJECTIVE

To evaluate whether critically ill children with systemic inflammatory response syndrome (SIRS) or sepsis have altered resting energy expenditure (REE) and substrate utilization.

SUMMARY BACKGROUND DATA

Studies in adults with sepsis have shown increased energy expenditure and mobilization of endogenous fat. In infants and children, energy metabolism and substrate utilization during sepsis have not been characterized.

METHODS

Metabolic studies were performed in 21 critically ill children with SIRS or sepsis. Twenty-one stable control children, matched for weight, were also studied. Seven patients required inotropic support and 17 received mechanical ventilation. Fifteen patients with SIRS had evidence of bacterial, fungal, or viral infection and were considered septic. Respiratory gas exchange was measured by computerized indirect calorimetry for 1 to 2 hours continuously.

RESULTS

The REE of patients with SIRS or sepsis was not different from that of controls. Similarly, there were no differences in carbon dioxide production and oxygen consumption. Resting energy metabolism was not different between patients with SIRS and patients with sepsis. In addition, the presence of low platelet count or inotropic support did not affect resting energy metabolism. The median respiratory quotient of patients with SIRS or sepsis was 0.88 (range 0.75-1.12), indicating mixed utilization of fat and carbohydrate; this was not significantly different from that of controls. The Pediatric Risk of Mortality Score was not significantly correlated with REE or respiratory quotient.

CONCLUSIONS

The energy requirements of children with SIRS or sepsis are not increased. Their resting metabolism is based on both carbohydrate and fat utilization. The authors speculate that these children divert the energy for growth into recovery processes.

The metabolic needs of critically ill children and neonates

The pediatric metabolic response to injury and operation is proportional to the degree of stress and causes an increase in the turnover of proteins, fats, and carbohydrates. Thereby, substrates are made readily available for the immune response and wound healing. Because this process requires energy, the resting energy expenditure of ill patients increases. Whole-body protein degradation rates are elevated out of proportion to synthetic rates, and negative protein balance also ensues. Neonates and children are particularly susceptible to the loss of lean body mass and its attendant increased morbidity and mortality caused by an intrinsic lack of endogenous stores and greater baseline requirements. An appropriately designed mixed fuel system of nutritional support replete in protein does not quell this metabolic response but can result in anabolism and continued growth in ill children. In addition, the use of adequate analgesia and anesthesia is a readily available and proven means of reducing the magnitude of the catabolism associated with operation and injury. Finally, as hormonal- and cytokine-mediated metabolic alterations are better understood, therapeutic interventions may become available to directly modulate the metabolic response to illness, thus potentially further improving clinical outcome in pediatric surgical patients.

Differential energy metabolism in conjoined twins

BACKGROUND/PURPOSE

Conjoined twins often have different body composition and growth rate before separation. This may be because of differences in energy metabolism. The aim of this study was to investigate the energy expenditure, body composition, and calorie intake of thoracopagus conjoined twins with shared hepatic circulation but separate gastrointestinal tracts.

METHODS

The twins were studied at two periods: (1) before separation (age, 73 days) and (2) after separation (age, 97 days). Calorie intake over the study periods was carefully documented. Respiratory gas exchange was measured by computerized indirect calorimetry. The postseparation weight ratio of twin A to twin B was used to approximate the preseparation weights. Body composition (total body fat) was calculated from skinfold thickness and anthropometric measurements.

RESULTS

The body composition of the twins was different: body weight and total body fat were higher in twin B. Resting energy expenditure and calorie intake were markedly different between the conjoined twins before separation. In both twins, the energy expenditure increased after separation. After separation, the resting energy expenditure of the twins was similar.

CONCLUSIONS

This study illustrates the difference in energy metabolism in a set of thoracopagus conjoined twins. The authors speculate that twin A was supplying nutrients to twin B resulting in increased energy expenditure before separation. This would explain the lower calorie intake and higher fat mass of twin B.

Metabolic response to neonatal surgery

The energy and protein metabolism of newborn infants differs from that of older individuals. Although energy expenditure and protein turnover are higher in newborn infants than in adults, the metabolic response to surgery in neonates has not been fully characterized. Preliminary studies indicate that metabolic response to operative stress is different in infants and adults: infants have an increased metabolic rate postoperatively for only 6 to 12 hours and do not have increased protein catabolism. More studies are needed in "stressed" newborn infants to further characterize substrate use and the metabolism of single organs.

Lipid peroxidation can be reduced in infants on total parenteral nutrition by promoting fat utilisation

BACKGROUND/PURPOSE

Increased oxygen-derived free radical activity has been reported during total parenteral nutrition (TPN) in infants and has been specifically linked to the fat infusion. The aim of this study was to test the hypothesis that during TPN, oxygen-derived free radical production can be reduced by increasing the utilisation of fat.

METHODS

In experiment A (17 patients) the fat infusion was kept constant (3 g/kg/d) and the carbohydrate infusion was changed from 18 g/kg/d on day 1 to 10 g/kg/d on day 2. In experiment B (six patients) the carbohydrate infusion remained constant and the fat infusion was changed from 3 g/kg/d on day 1 to 0 g/kg/d on day 2. Fat utilisation was measured by indirect calorimetry. Plasma malondialdehyde, an index of lipid peroxidation resulting from increased oxygen-derived free radical activity, was measured by a colorimetric assay.

RESULTS

In both experiments there was no significant change between the two study phases in oxygen consumption, carbon dioxide production, and resting energy expenditure demonstrating that the patients were metabolically stable. In experiment A there was a significant (P = .0005) increase in fat utilisation and a significant (P = .009) decrease in malondialdehyde (MDA) concentration between the two phases. In experiment B there was also a significant (P = .007) decrease in MDA concentration. The decrease in MDA concentration was similar between the two experiments.

CONCLUSIONS

It is not necessary to stop the infusion of fat to reduce free radical production. Promoting fat utilisation by reducing the carbohydrate-fat ratio of the TPN reduces free radical activity to a similar extent as fat exclusion. These findings have important implications for the composition of TPN.

Characteristics of protein and energy metabolism in neonates with necrotizing enterocolitis--a pilot study

BACKGROUND/PURPOSE

It is assumed that neonates with necrotizing enterocolitis (NEC) are hypermetabolic. However, the dynamics of protein and energy metabolism in neonates with NEC have not been characterized. The purpose of this study was to test the hypothesis that protein turnover and energy expenditure are increased during the acute stage of NEC and later return to normal values.

METHODS

A pilot study was performed on six neonates with proven NEC (Bell's stage II or III). Patients were studied in two phases: (1) in the acute stage of their disease and (2) when their clinical condition had stabilized. Whole-body protein turnover was calculated using an intravenous infusion of [1-13C] leucine and by measuring the isotopic enrichment of plasma [13C]alpha-ketoisocaproic acid and 13CO2. Respiratory gas exchange was measured simultaneously by computerized indirect calorimetry.

RESULTS

Median gestational age was 36 weeks (range, 28 to 40) with a median postnatal age of 21 days (range, 6 to 47). All patients recovered from the acute episode, although three patients died after recovering from the acute disease from other conditions. The patients studied showed marked variability in protein metabolism kinetics. However, there was no difference in whole-body protein flux between the acute phase (7.6 g/kg/d; range, 5.6 to 18.2) and the recovery phase (7.0 g/kg/d; range, 6.9 to 12.2; P = .89). Furthermore, there was no difference in any of the component parts of wholebody protein turnover. Resting energy expenditure did not change between the acute phase (42.8 kcal/kg/d; range, 34.4 to 52.5) and the recovery phase (51.0 kcal/kg/d; range, 34.9 to 55.3; P = .18).

CONCLUSIONS

This pilot study shows that the rates of protein and energy metabolism in neonates with NEC are comparable with reported values in stable neonates. There was no difference in protein or energy dynamics between study phases. The authors speculate that neonates with NEC may divert the products of protein synthesis from growth to tissue repair.

Effect of major abdominal operations on energy and protein metabolism in infants and children

PURPOSE

The authors attempted to test the hypothesis that infants and children increase whole-body protein flux and energy metabolism during the early postoperative period.

METHODS

Ten infants and children (age range, 2 days to 3 years; weight range, 1.5 to 14.2 kg) who had undergone a major operation were studied. Anaesthesia was standardised, and operative stress score (OSS) recorded. Patients were studied for 4 hours preoperatively and for the first 6 hours after surgery. Respiratory gas exchange was measured by computerised indirect calorimetry. The components of whole-body protein turnover were estimated by giving an intravenous infusion of [1-13C]leucine, and by measuring the isotopic enrichment of plasma [13C]alpha-ketoisocaproic acid by gas chromatograph mass spectrometry and 13CO2 enrichment by isotope ratio mass spectrometry.

RESULTS

Median duration of the operation was 73.5 minutes (range, 28 to 285 minutes) with a OSS of 8 (range, 7-17). There were no significant differences in oxygen consumption and resting energy expenditure between the two study phases. The respiratory quotient (RQ) fell from a preoperative value of 0.92 (range, 0.81 to 1.08) to 0.89 (range, 0.79 to 0.95) postoperatively (P = .04). The authors found no significant differences in the rates of whole body protein flux, protein synthesis, amino acid oxidation, and protein degradation between the study phases.

CONCLUSIONS

Infants and children do not increase their whole-body protein turnover and metabolic rate after major operations. The observed decrease in RQ reflects mobilisation of endogenous fat. We speculate that the lack of catabolism observed in children is caused by a diversion of protein synthesis from growth to tissue repair.

Energy requirements of surgical newborn infants receiving parenteral nutrition

The energy requirement for mature newborn infants receiving total parenteral nutrition is approximately 100 kcal.kg-1.d-1. There is no necessity to increase the caloric intake after an uncomplicated operation. Energy requirements are affected by the maturity of the infant, the degree of operative stress, opioid medication, and the presence or absence of sepsis. In general, glucose intake should not exceed the resting energy expenditure. Glucose administration exceeding 18 g.kg-1.d-1 is associated with lipogenesis and reduced oxygenation of exogenous lipid. Resting energy expenditure varies widely between infants, and energy intake, based on clinical and biochemical monitoring, should be adjusted for individual patients.

Early postoperative alterations in infant energy use increase the risk of overfeeding

AIM OF STUDY

Energy needs in infants are decreased after surgery because of growth inhibition (resulting from catabolic stress metabolism), decreased insensible losses, and inactivity. Using standardized formulas that account for growth, activity, and insensible losses during this stress period can lead to overfeeding in excess of 200% of the actual measured requirement. Overfeeding during this acute injury period can result in increased CO2 production from lipogenesis. This study determined the effects of a reduced rate of mixed caloric repletion on infant energy use during the early postoperative period.

METHODS

C-reactive protein (CRP), oxygen consumption (VO2), carbon dioxide production (VCO2), measured energy expenditure (MEE), and total urinary nitrogen (TUN) were measured serially in seven infants (average age, 78 days) during the first 72 hours after abdominal or thoracic surgery. Nonprotein respiratory quotient (RQnp), and values for oxidation of carbohydrate (Ce) and fat (Fe) were calculated. Injury severity was stratified based on serum CRP concentrations of > or = 6.0 mg/dL (high stress) or < 6.0 mg/dL (low stress). Recovery from acute stress was analyzed by comparing studies in which CRP had decreased to < or = 2.0 mg/dL (resolving stress group) with those in which CRP values were greater than 2.0 mg/dL (acute stress group).

RESULTS

Average total caloric intake (64.56 +/- 18.51 kcal/kg/d; approximately 50% of predicted energy requirement) exceeded average MEE (42.90 +/- 9.98 kcal/kg/d) by approximately 50%. Average TUN was 0.18 +/- 0.07 g/kg/d (high stress 0.2 +/- 0.05 versus low stress 0.16 +/- 0.09 g/kg/d). Average RQnp was 1.05 +/- 0.13 and average Ce was 37.28 +/- 16.86 kcal/kg/d. The average calculated Fe was 0.0 +/- 12.27 kcal/kg/d, reflecting approximately equal amounts of fat oxidized compared with fat generated from excess glucose (lipogenesis). When individual studies were analyzed at a CRP cutpoint of 2.0 mg/dL, overfeeding (RQ > 1.0) was significantly less likely in the resolving (2/6 studies, 33.4%) versus acute stress (9/13 studies, 69.2%, Z test P < .001) group. Five of seven (5/7) patients (9/19 individual studies) had negative Fe values (average -9.89 +/- 10.02) reflecting net lipogenesis. The RQnp for these nine studies was 1.14 +/- 0.11 versus 0.97 +/- 0.09 for the remaining 10, and this difference was significant (P < .01). A significant correlation existed between carbohydrate intake and VCO2 (Pearson r = .6951, P < .01). In addition, there was a good correlation between carbohydrate intake and VCO2 (Pearson r = .6591, P < .01). The coefficient of variation for MEE was 8.0% (low stress) versus 30.2% (high stress).

CONCLUSION

Lipogenesis with increased CO2 production is substantial, even at reduced caloric delivery rates that exceeded MEE by only 50%, during the early postoperative acute metabolic stress period in infants. These data suggest that caloric requirements during stress are likely equal to or only minimally in excess of actual MEE. Intersubject variability, especially in more severely stressed infants, underscores the importance of serial measurements of energy expenditure to enable precise caloric delivery and avoid overfeeding. In the absence of calorimetric measurement, the data suggest that PBMR (predicted basal metabolic rate) should be used to estimate caloric delivery until CRP values are < or = 2.0 mg/dL.

Protein metabolism kinetics in neonates: effect of intravenous carbohydrate and fat

The aim of this study was to determine the effect of different glucose/fat ratios on protein metabolism kinetics in newborn infants receiving total parenteral nutrition (TPN). Eighteen studies were done on 14 infants receiving TPN (weight 3.15 +/- 0.22 kg [mean +/- SEM]; gestational age 37.8 +/- 0.9 weeks; postnatal age 14.0 +/- 3.7 days). There were two study groups. Group A infants (n = 9) received 10.0 g/kg/d of dextrose and 4.0 g/kg/d of fat; group B infants (n = 9) received 19.0 g/kg/d of dextrose and 0.5 g/kg/d of fat. Caloric intake (86 kcal/kg/d) and amino-acid intake (2.5 g/kg/d) were the same in the two groups. There was no difference between the groups with regard to weight, gestational age, and postnatal age. Intravenous diet was constant during the 3-day study period. Timed urinary nitrogen excretion was determined. On day 3 of the study, each infant received a priming dose of 15 mumol/kg of [13C]leucine followed by a 6-hour infusion at 6 mumol/kg/h. Plasma and breath samples were taken at hourly intervals, and CO2 production was measured by indirect calorimetry. Plateau levels of plasma [13C]-alpha Ketoisocaproic acid (KIC) enrichment and expired 13CO2 enrichment were determined by gas chromatograph mass spectrometry. Protein metabolism kinetics were calculated. Results were: nitrogen balance 0.27 +/- 0.01 g/kg/d, total protein flux 10.38 +/- 0.34 g/kg/d, total protein synthesis 9.64 +/- 0.31 g/kg/d, total protein breakdown 7.86 +/- 0.38 g/kg/d, and total protein oxidation/excretion 0.92 +/- 0.04 g/kg/d.(ABSTRACT TRUNCATED AT 250 WORDS)

A new equation to predict the resting energy expenditure of surgical infants

It is essential that adequate calories are provided to newborns to cover their energy expenditure. This is difficult to measure and varies significantly between individuals. The aim of this study was to develop an equation to predict the basal energy requirements of stable surgical infants, using easily measurable parameters. Resting energy expenditure (REE) was measured using computerized open-circuit indirect calorimetry. One hundred twenty-two measurements were made on different days in 46 stable nonventilated infants. The measured REE was 34.41 +/- 0.46 cal/kg/min; (mean +/- SEM). Three body-size measurements correlated significantly with REE (cal/min): weight in kilograms (r = .87; P < .00001), body surface area in square meters (r = .86; P < .00001), and lean body mass in kilograms (r = .81; P < .00001). Five other independent variables correlated significantly with REE (cal/kg/min): heart rate in beats per minute (r = .60; P < .00001), postnatal age in days (r = .49; P < .00001) caloric intake in cal/kg/min (r = .44; P < .00001), gestational age in weeks (r = .43; P < .00001), and rectal temperature in degrees Celsius (r = .19; P = .04). Weight, heart rate, age, gestational age, and temperature were regarded as independent predictor variables of REE for the multiple stepwise regression analysis. Three variables entered this highly significant equation: REE (cal/min) = -74.436 + (34.661 x weight in kg) + (0.496 x heart rate in beats/min) + (0.178 x age in days) (r = .92; F = 230.07; significance, F < .00001).(ABSTRACT TRUNCATED AT 250 WORDS)

Postoperative changes in resting energy expenditure and interleukin 6 level in infants

The relationship was determined between resting energy expenditure (REE) and interleukin (IL)6 level following surgery in infants. Sixteen infants of mean(s.e.m.) weight 3.2(0.2) kg undergoing uncomplicated surgery were studied. The operative stress score was recorded and plasma IL-6 levels were measured before and 4, 8, 12 and 24 h after surgery. Respiratory gas exchange was measured by indirect calorimetry before and at 2, 4, 6, 8, 10, 12, 24 and 48 h. Urinary nitrogen excretion was measured and calculated. IL-6 levels increased significantly after surgery (P = 0.006) and were maximal at 12 h. There was a linear correlation between the increase in IL-6 level and operative severity score (r = 0.61, P = 0.012). REE increased significantly after operation (P < 0.001), peaking at 2-4 h, and returned to baseline levels by 12 h. The changes in REE preceded those in IL-6. IL-6 is a marker of the stress response in infants and may play a role in the subsequent modulation of this response.

The metabolic response to operative stress in infants

The aim of this study was to characterize energy metabolism and substrate utilization in infants following an operation. Nineteen infants (weight 3.2 +/- 0.2 kg) who had an operation were studied. Anesthesia was standardized and operative stress score (OSS) was recorded. Five infants had a minor operation (OSS < 7), and 14 infants had a major operation (OSS > or = 7). Energy and nitrogen intake were constant during the 48-hour study period. Respiratory gas exchange was measured by indirect calorimetry preoperatively, and postoperatively for the first 12 hours continuously and at 24 hours, 48 hours, and 5 days. Urinary nitrogen excretion rate was measured for the first 48 hours following the operation. Physical activity was scored. Resting energy expenditure (REE) and nonprotein respiratory quotient (NPRQ) were calculated. REE increased postoperatively, peaking at 2 to 4 hours, and returned to baseline levels by 12 to 24 hours. Peak REE was significantly higher than baseline REE (P < .001). Substrate utilization was not altered by operation. The increase in REE was significantly greater in infants having a major operation than in infants having a minor operation (P < .05). Among infants having a major operation, the increase in REE was significantly greater in those infants more than 48 hours old, than in those infants less than 48 hours old (P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Glucose utilization in the surgical newborn infant receiving total parenteral nutrition

Glucose is the main source of nonprotein calories in total parenteral nutrition (TPN). However, its use has been associated with various nutritional, metabolic, and respiratory complications. The aim of this study was to determine, in the stable surgical newborn infant, the characteristics of carbohydrate metabolism, in particular the maximum oxidative threshold for intravenous glucose and the thermogenic effect of glucose. Twenty-one studies were done on 11 infants (weight 2.82 +/- 0.19 kg) receiving TPN containing constant amounts of amino acids (2.5 g/kg/d) and fat (3.0 g/kg/d), and different amounts of glucose (range, 10 to 25 g/kg/d). Oxygen consumption (VO2), carbon-dioxide production (VCO2), and resting energy expenditure (REE) were measured by indirect calorimetry. Urinary nitrogen excretion rate was measured and substrate utilization calculated from the nonprotein respiratory quotient (NPRQ). There was a positive correlation between the predictor variable glucose intake and the dependent variables VO2 (r = .55; P < .05), VCO2 (r = .83; P < .0001), REE (r = .65; P < .005), NPRQ (r = .94; P < .0001), respiratory rate (r = .46; P = .06), and plasma triglycerides level (r = .67; P < .01). When glucose intake exceeded 18 g/kg/d the NPRQ was greater than 1.0, indicating glucose conversion to fat. Above this level of intake, the gradient of the correlation between the predictor variable glucose intake and the dependent variables VCO2 and REE increased. From this study we conclude that: (1) Glucose intake is the principal determinant of glucose utilization and exerts an influence on the metabolism of exogenous fat.(ABSTRACT TRUNCATED AT 250 WORDS)

A method for urine collection in infants

A simple, inexpensive, non-invasive method for urine collection was used in 28 consecutive infants for periods of 48 hours (n = 10) and 72 hours (n = 18). The incidence of urine collector detachment was low on the first and second days (< 4%) and increased significantly on the third day (28%). Volume of urine leaked was < 4% of the total volume collected daily. This method is applicable to both sexes and is reliable for up to 48 hours.

Absence of hypermetabolism after operation in the newborn infant

This study was designed to assess the effect of operative stress on resting energy expenditure (REE) in the newborn infant. In 13 neonates who had an uncomplicated abdominal, thoracic, or spinal operation, REE was measured both preoperatively and on the third postoperative day. The mean preoperative REE of 43.19 +/- 7.95 kcal/kg per day was not significantly different from the mean postoperative REE of 41.70 +/- 7.94 kcal/kg per day. Sixteen neonates had REE measured on the first, second, and seventh postoperative days. The mean postoperative REE values of 43.12 +/- 6.92, 42.41 +/- 7.58, and 46.33 +/- 6.89 kcal/kg per day at 1, 2, and 7 days, respectively, were not significantly different from the preoperative REE. There was no significant difference in oxygen consumption, carbon dioxide production, and respiratory quotient between the preoperative and postoperative groups. In this study, an uncomplicated operation did not increase REE in the neonate.