Metabolic consequences of intrauterine growth retardation in very low birthweight infants

By the combination of energy and macronutrient balances, continuous open circuit computerized indirect calorimetry, and anthropometry, we have compared small for gestational age (SGA) and appropriate for gestational age (AGA) very low birthweight infants with respect to metabolizable energy intake (mean +/- SE: 125.9 +/- 2.5 versus 130.4 +/- 3.5 kcal/kg X day), energy expenditure (67.4 +/- 1.3 versus 62.6 +/- 0.9 kcal/kg X day), storage of energy and macronutrients and growth. Fourteen studies in six SGA infants (gestational age, 33.1 +/- 0.3 weeks; birthweight, 1120 +/- 30 g) and 22 studies in 13 AGA infants (gestational age, 29.3 +/- 0.4 weeks; birthweight, 1155 +/- 40 g) were performed. The SGA infants had a lower absorption of fat (68.7 +/- 3.2 versus 79.7 +/- 1.7%) and protein (69.1 +/- 3.2 versus 83.4 +/- 1.5%) and hence increased (P less than 0.001) energy loss in excreta (29.9 +/- 2.8 versus 18.2 +/- 1.5 kcal/kg X day). The significant hypermetabolism of SGA infants by 4.8 kcal/kg X day was associated with an increased fat oxidation. Despite lower energy storage, SGA infants were gaining weight (19.4 +/- 0.9 g/kg X day), length (1.25 +/- 0.14 cm/week), and head circumference (1.16 +/- 0.9 cm/week) at higher rates than the AGA group. The energy storage per g weight gain was lower (P less than 0.001) in the SGA group (3.0 +/- 0.14 versus 4.26 +/- 0.26 kcal) reflecting higher water, lower fat (22.2 +/- 1.8 versus 33.8 +/- 2.5%; P less than 0.001) and lower protein (7.7 +/- 0.5 versus 12.5 +/- 0.8%; P less than 0.001) contents of weight gain in the SGA group.     

Energy expenditure and deposition of breast-fed and formula-fed infants during early infancy

The energy intake, expenditure, and deposition of 40 breast-fed and formula-fed infants were investigated at 1 and 4 mo of age to explore possible differences in energy utilization between feeding groups. Energy intake was calculated from 5-d test-weighing records or pre- and postweighing of formula bottles, in combination with bomb calorimetry of the milks. Total daily energy expenditure (TDEE) was determined by the doubly labeled water method. Sleeping metabolic rate (SMR) and minimal observable energy expenditure were measured by indirect calorimetry. Activity was estimated as the difference between TDEE and SMR. Energy deposition was estimated from dietary intake and TDEE. Energy intakes were significantly higher for the formula-fed than breast-fed infants at 1 mo (118 +/- 17 versus 101 +/- 16 kcal/kg/d) and 4 mo (87 +/- 11 versus 72 +/- 9 kcal/kg/d) (p less than 0.001). TDEE averaged 67 +/- 8 and 64 +/- 7 kcal/kg/d at 1 mo and 73 +/- 9 and 64 +/- 8 kcal/kg/d at 4 mo for the formula-fed and breast-fed infants, respectively, and differed between feeding groups (p less than 0.04). SMR and minimal observable energy expenditure (kcal/min) were higher among the formula-fed infants at 1 and 4 mo (p less than 0.005). The energy available for activity and the thermic effect of feeding did not differ between feeding groups. Rates of weight gain (g/d) and energy deposition (kcal/kg/d) tended to be greater among the formula-fed infants at 1 and 4 mo (p less than 0.006).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of intermittent versus continuous enteral feeding on energy expenditure in premature infants

The purpose of this study was to examine whether premature infants have higher rates of energy expenditure and diet-induced thermogenesis during intermittent feeding compared with continuous feeding. Using open-circuit respiratory calorimetry, we measured energy expenditure in 11 premature newborn infants on 2 successive days for 5 to 7 hours during and after either intermittent or continuous feeding. Infants were fed the same quantity of formula each day, either for 5 minutes or by continuous drip for 2 to 3 hours. The order of feeding type was randomized. No response of diet-induced thermogenesis to continuous feeding was found, whereas a peak increase of 15% over baseline was observed after intermittent feeding. Overall energy expenditure during the study period was significantly greater after intermittent compared with continuous feeding (2.18 +/- 0.07 kcal/kg per hour vs 2.09 +/- 0.05 kcal/kg per hour; p less than 0.05). Thus there was a mean 4% difference (range up to 17%) in energy expenditure between the two feeding modes. These results are similar to those obtained with adults and support the concept of the increased energy efficiency of continuous feeding. Further study will be necessary to document whether the increased energy efficiency provided by continuous feeding may be clinically significant.     

Supplementation of pooled human milk with casein hydrolysate: energy and nitrogen balance and weight gain composition in very low birth weight infants

Growth and nitrogen and energy balances were studied with a combined technique of nutrient balance and indirect calorimetry measurement in two groups of eight very low birth weight infants fed pooled pasteurized human milk (HM) or cow's milk casein hydrolysate supplemented HM (HM-Pr). There was no difference in the amount of energy absorbed (91 +/- 17 kcal/kg/day with HM-Pr versus 95 +/- 8 with HM-P) or in the growth rate. The infants fed HM-Pr had a higher nitrogen intake (602 +/- 80 versus 395 +/- 64 mg/kg/day; p less than 0.001), urinary nitrogen excretion (160 +/- 64 versus 78 +/- 16 mg/kg/day; p less than 0.005) and nitrogen retention (326 +/- 32 versus 252 +/- 48 mg/kg/day; p less than 0.01). They also had increased plasma concentrations of essential amino acids, urea nitrogen, and total protein without metabolic imbalance. Energy expenditure was higher (58 versus 49 kcal/kg/day; p less than 0.005) and energy storage lower (33 versus 47 kcal/kg/day; p less than 0.05) with HM-Pr. In percent of weight gain, protein and fat accretion represented 12 and 14% in HM-Pr group versus 10 and 27% in HM group. Very low birth weight infants fed casein hydrolysate supplemented pooled HM achieved a growth rate and a weight gain composition similar to the fetus.     

Total but not resting energy expenditure is increased in infants with ventricular septal defects

OBJECTIVE: The purpose of this study was to determine the effect of left-to-right shunting on the resting energy expenditure (REE), total energy expenditure (TEE), and energy intake in a group of 3- to 5-month-old infants with moderate to large unrepaired ventricular septal defects (VSDs) compared with age-matched, healthy infants. METHODS: Eight infants with VSDs and 10 healthy controls between 3 to 5 months of age participated in the study. Indirect calorimetry was used to measure REE and the doubly-labeled water method was used to measure TEE and energy intake. An echocardiogram and anthropometric measurements were performed on all study participants. Daily urine samples were collected at home for 7 days. Samples were analyzed by isotope ratio mass spectrometry. Data were compared using analysis of variance. RESULTS: No significant differences were found in REE (VSD, 42.2 +/- 8.7 kcal/kg/d; control, 43.9 +/- 14.1 kcal/kg/d) or energy intake (VSD, 90.8 +/- 19.9 kcal/kg/d; control, 87.1 +/- 11.7 kcal/kg/d) between the groups. The percent total body water was significantly higher in the VSD infants and the percent fat mass was significantly lower. TEE was 40% higher in the VSD group (VSD, 87.6 +/- 10.8 kcal/kg/d; control, 61.9 +/- 10.3 kcal/kg/d). The difference between TEE and REE, reflecting the energy of activity, was 2.5 times greater in the VSD group. CONCLUSIONS: REE and energy intake are virtually identical between the two groups. Despite this, infants with VSDs have substantially higher TEE than age-matched healthy infants. The large difference between TEE and REE in VSD infants suggests a substantially elevated energy cost of physical activity in these infants. These results demonstrate that, although infants with VSDs may match the energy intake of healthy infants, they are unable to meet their increased energy demands, resulting in growth retardation.     

Energy expenditure, lipolysis, and glucose production in preterm infants treated with theophylline.

Theophylline is administered to preterm infants with pulmonary disease to improve pulmonary function and reduce apneic episodes. Because it potentially mediates both alpha- and beta-receptor-effector mechanisms, we tested the hypothesis that it increases lipolysis, gluconeogenesis from glycerol, and energy expenditure in 16 preterm infants, eight of whom were treated therapeutically with theophylline for apnea of prematurity (T) and eight of whom were controls (C). Mean +/- SD postnatal ages were 4.8 +/- 1.9 wk (T) and 2.4 +/- 0.9 wk (C) (p < 0.01). Corrected gestational ages were 35 +/- 1.6 wk (T) and 34 +/- 0.5 wk (C) (p = NS). Body weights were 1.69 +/- 0.13 kg (T) and 1.70 +/- 0.23 kg (C) (p = NS). All infants were clinically stable, breathing room air, fed enterally, and receiving no diuretics, steroids, or antibiotics. Lipolysis, hepatic glucose production, and gluconeogenesis from glycerol were measured using [2-13C]glycerol and [6,6-3H2] glucose tracers. Body water and energy expenditure were measured by the 2H2(18)O method. Body water volumes were 68.5 +/- 3.4% body weight (T) and 70.2 +/- 3.4% (C) (p = NS), suggesting fat was 10-13% of body weight in both groups. Mean daily energy expenditure was 65 +/- 22 kcal/kg body weight/d (T) versus 59 +/- 5 kcal/kg body weight/d (C) (p = NS). Between 4 and 6 h after a feeding, glucose production rates were 40.5 +/- 4.3 mumol/kg/min (T) and 37.6 +/- 4.8 mumol/kg/min (C) (p = NS).(ABSTRACT TRUNCATED AT 250 WORDS)     

Energy expenditure and energy intake during dexamethasone therapy for chronic lung disease.

Dexamethasone is commonly administered to ventilator-dependent preterm infants with chronic lung disease. Infants receiving dexamethasone therapy frequently exhibit decreased rates of weight gain. The purpose of this investigation was to determine whether decreased growth in infants receiving dexamethasone therapy is caused by increased energy expenditure. Twelve infants were studied: 6 received dexamethasone treatment at 2 wk of age and crossed over to receive placebo treatment at 4 wk; the treatment order was reversed in the other 6 infants. The doubly labeled water method was used to determine energy expenditure for a 1-wk period during each treatment phase. The rate of weight gain during dexamethasone treatment was 6.5+/-10.6 and 20.0+/-5.7 g/kg/d during placebo treatment. Energy expenditure was 93.1+/-34.6 kcal/kg/d during dexamethasone treatment and 88.3+/-37.1 kcal/kg/d during placebo treatment. Energy intake was 119.2+/-29.0 kcal/kg/d during dexamethasone treatment and 113.8+/-23.7 kcal/kg/d during placebo treatment. The difference between intake and expenditure, or the energy available for growth, was 26.2+/-36.8 kcal/kg/d during dexamethasone treatment and 25.5+/-37.4 kcal/kg/d during placebo treatment. No significant differences were found in energy expenditure or energy intake between the treatment phases. The reduced growth seen in infants receiving dexamethasone treatment cannot be explained by increased energy expenditure or decreased energy intake, but may be due to differences in the composition of newly accreted tissue.     

Energy balance in low birth weight infants fed formula of high or low medium-chain triglyceride content

We tested the effect on energy balance of the partial substitution of medium-chain for long-chain triglycerides in the diet of growing low birth weight infants. Fifteen infants were studied in a randomized double-blind crossover clinical trial in which each infant was fed each of two formulas, which were of equal gross energy and protein content but differed in fat composition. The high medium-chain triglyceride (MCT) formula contained medium- and long-chain triglycerides in a weight/weight ratio of 46:54; in the low MCT formula the ratio was 4:96. The hypothesis tested was that under conditions of equal gross energy intake the two diets would differ in their digestible and metabolizable energy contents and would produce differences in the infants' rates of energy expenditure and energy storage. Gross energy intakes averaged 562 and 555 kJ/kg/day (134 and 133 kcal/kg/day) with the high and low MCT formulas, respectively. With each diet, coefficients of energy digestibility (0.93) and metabolizability (0.91) were identical; the rates of energy expenditure were 262 (high MCT) and 265 (low MCT) kJ/kg/day (63 kcal/kg/day for both diets), and of energy storage were 246 (high MCT) and 239 (low MCT) kJ/kg/day (59 and 57 kcal/day). These differences were not significant. There were also no significant differences between the two diets in coefficients of nitrogen retention (mean 0.70) or in rate of weight gain (mean 21.5 gm/kg/day). The use of high MCT content in infant formula neither provided a nutritional advantage in energy digestibility or metabolizability nor resulted in an increased rate of energy expenditure or of energy storage.     

Energy expenditure in human milk- versus formula-fed preterm infants

OBJECTIVE: We compared energy expenditure (EE) of preterm infants fed their mother's milk versus preterm infant formula.Study design A prospective, randomized crossover study of 13 healthy, appropriate weight for gestational age, gavage-fed, preterm infants. Before the study and according to our feeding protocol, infants uniformly received alternate feeds of human milk and formula. Each infant was randomly assigned to 24 hours of formula feeding followed by 24 hours of breast milk or the reverse. Infants were studied asleep, at the end of each 24-hour period. EE was measured by indirect calorimetry 1 hour before feeding, 20 minutes during feeding, and 1 hour after feeding in a servo-controlled convective incubator. Energy content of human milk was analyzed by bomb calorimetry. RESULTS: EE was significantly lower in breast milk-fed infants during prefeeding (52+/-6 vs 57+/-10 kcal/kg per 24 hours) (P<.05), per feeding (55+/-6 vs 60+/-10 kcal/kg per 24 hours) (P<.05), and at the postfeeding measurement (60+/-7 vs 65+/-7 kcal/kg per 24 hours) (P=.059). After correction of the results for the actual measured energy intake, all statistical differences reached the <.05 level. CONCLUSIONS: Preterm infants have lower EE when they are fed breast milk than when they are fed preterm infant formula.     

Increased energy expenditure and fecal fat excretion do not impair weight gain in small-for-gestational-age preterm infants.

In order to optimize the nutrition of high-risk premature infants beyond the early postnatal period, a more precise knowledge of individual nutritional requirements is needed. We therefore studied the influence of intrauterine growth retardation on energy expenditure and nutrient utilization determined by indirect calorimetry and fecal fat excretion (steatocrit) in nineteen premature infants who were appropriate-for-gestational-age (AGA; mean gestational age 29.9+/-0.3 weeks, mean birth weight 1.30+/-0.05 kg) and thirteen small-for-gestational-age (SGA) premature infants [mean gestational age 32.4+/-0.5 weeks, mean birth weight 1.024+/-0.07 kg (i.e., below the 10th percentile)] during the first and second month of life. All infants were clinically stable during the study period. In nine SGA infants we observed a significantly higher steatocrit compared to twelve AGA infants (29+/-1 vs. 17+/-1% p = 0.0001). SGA infants (n = 12) also showed a slightly (albeit statistically not significantly) higher energy expenditure than AGA infants (n = 15) (58.7+/-1.9 vs. 53.6+/-1.5 kcal/kg per day, p = 0.054). Despite the increased fat excretion and higher energy expenditure, SGA infants gained weight more rapidly during the study period than AGA infants (20+/-1 vs. 17+/-1 g/kg per day, p = 0.026). We conclude that influences of intrauterine growth retardation on energy expenditure and nutrient utilization persist during the first weeks of extrauterine life. However, these metabolic changes do not impair the capability of SGA infants for extrauterine catch-up growth if adequate nutrition is provided.     

New equations for calculating the components of energy expenditure in infants

OBJECTIVES: To derive new equations for 24-hour energy expenditure (24-h EE; kcal/d) and resting (RMR; kcal/d) and sleeping metabolic rates (SMR; kcal/d) in young infants by using the Enhanced Metabolic Testing Activity Chamber (EMTAC). METHODS: Data from 50 (25 male/25 female) healthy normally growing infants (4.9 +/- 1.6 months, 7.1 +/- 1.4 kg, 65 +/- 5 cm) who had 24-h EE, RMR, and SMR extrapolated from 4- to 6-hour metabolic measurements in the EMTAC were used to derive new equations for 24-h EE, RMR, and SMR. Equations were derived by means of multiple regression analysis (SPSS 8.0), with weight alone or with length and weight entered as independent variables. Similar data from 10 additional test infants (4 male/6 female, 5.1 +/- 0.6 months, 7.5 +/- 1.0 kg, 65 +/- 5 cm) were used to cross-validate the new equations. RESULTS: Twenty-four-hour EE, RMR, and SMR were 79.6 +/- 19.2, 66.8 +/- 15.1, and 62.3 +/- 10.3 kcal/kg per day, respectively. No differences existed in RMR (kcal/kg per day) from the 10 test infants between the weight (68.6 +/- 1.9) and height-weight based equations (68.4 +/- 6.1) or that measured by the EMTAC (67.6 +/- 10.2). Weight was the major predictor of 24-h EE, RMR, and SMR. The WHO, Schofield-weight and weight-height equations underestimated (P <.05) by 19%, whereas the new equations were within 4% of RMR obtained from the EMTAC. CONCLUSIONS: The new equations for assessing energy requirements in healthy infants are more accurate than those previously published that underestimated 24-h EE by 15 kcal/kg per day.     

Validation of a [13C]bicarbonate tracer technique to measure neonatal energy expenditure

The use of a stable isotope-labeled [13C]bicarbonate infusion to measure energy expenditure is advantageous, as a complete collection of expired air is not required. This technique allows for facile measurements of energy expenditure in intubated neonates. The aim of the present study was to determine the accuracy of energy expenditure estimates in postsurgical neonates by using the [13C]bicarbonate method compared with the current standard, indirect calorimetry. Eight neonates who were receiving total parenteral nutrition [98 +/- 21 (SD) kcal x kg(-1) x d(-1); 3.1 +/- 0.7 (SD) protein g x kg(-1) x d(-1)] were studied on postoperative d 15.5 +/- 11.9. A primed continuous 3-h intravenous infusion of NaH13CO3 and indirect calorimetry were performed simultaneously. Energy expenditure was calculated separately from the Weir equation and from the dilution of 13CO2 in the breath in combination with the individual energy equivalents of CO2 from the diet. The rate of CO2 appearance and energy expenditure calculated from the bicarbonate method (0.725 +/- 0.021 mol x kg(-1) x d(-1); 89.5 +/- 2.5 kcal x kg(-1) x d(-1)) highly correlated (r = 0.94 and 0.98, respectively) with the CO2 excretion and energy expenditure determined by indirect calorimetry (0.489 +/- 0.016 mol x kg(-1) x d(-1); 60.2 +/- 2.0 kcal x kg(-1) x d(-1)) when analyzed nonproportionately to weight. Bland-Altman analysis demonstrated the 95% confidence interval to be +/- 8.2 kcal x kg(-1) x d(-1). Linear regression analysis revealed a highly statistically significant equation relating the two energy expenditures: Indircal (kcal/d) = -9.341 + [0.705 x Bicarb (dcal/d)]; p < 0.001, r2 = 96.4%. We conclude that energy expenditure in neonates can be accurately determined using the [13C]bicarbonate method and a regression equation. Therefore, the bicarbonate method may be useful for determining energy expenditure in neonates not readily accessible to indirect calorimetry, such as those being mechanically ventilated or on extracorporeal life support.     

Formula intake of 1- and 4-month-old infants

This study was designed to estimate energy intake in exclusively formula-fed infants. Formula intake of twenty-four 1- and 4-month-old infants was studied for 5 consecutive days; six boys and six girls were in each age group. Intake was estimated by laboratory-determined weights of formula consumed, spilled, and regurgitated. Two additional methods were used to estimate intake in the first nine infants during the 1st day of observation: test-weighing the infant at each feeding and mother's weighing of formula consumed, regurgitated, and spilled at each feeding. No consistent differences were detected among methods, but test-weighing appeared to have the greatest feed-to-feed variability. Intake was estimated to be 747 +/- 100 g or 125.5 +/- 17 kcal/kg, and 958 +/- 131 g or 94.0 +/- 13 kcal/kg for 1- and 4-month-old infants, respectively. The day-to-day variability (expressed as the coefficient of variation) was 13 and 15% (CV, g/kg) for 1- and 4-month-old infants, respectively. Between-infant variability of intake was approximately 8% (CV, g/kg) for both age groups. Energy intakes of 1-month-old formula-fed infants were similar to published values of breast-fed infants of similar age, but the energy intakes of 4-month-old formula-fed infants were significantly higher than values published for 4-month-old breast-fed infants.     

Whole body protein synthesis and energy expenditure in very low birth weight infants

The aim of the present work was to study whole body protein synthesis and breakdown, as well as energy metabolism, in very low birth weight premature infants (less than 1500 g) during their rapid growth phase. Ten very low birth weight infants were studied during their first and second months of life. They received a mean energy intake of 114 kcal/kg X day and 3 g protein/kg X day as breast milk or milk formula. The average weight gain was 15 g/kg X day. The apparent energy digestibility was 88%, i.e. 99 kcal/kg X day. Their resting postprandial energy expenditure was 58 kcal/kg X day, indicating that 41 kcal/kg X day was retained. The apparent protein digestibility was 89%, i.e. 2.65 g/kg X day. Their rate of protein oxidation was 0.88 g/kg X day so that protein retention was 1.76 g/kg X day. There was a linear relationship between N retention and N intake (r = 0.78, p less than 0.001). The slope of the regression line indicates a net efficiency of N utilization of 67%. Estimates of body composition from the energy balance, coupled with N balance method, showed that 25% of the gain was fat and 75% was lean tissue. Whole body protein synthesis and breakdown were determined using repeated oral administration of 15N glycine for 60-72 h, and 15N enrichment in urinary urea was measured. Protein synthesis averaged 11.2 g/kg X day and protein breakdown 9.4 g/kg X day. Muscular protein breakdown, as estimated by 3-methylhistidine excretion, contributed to 12% of the total protein breakdown.(ABSTRACT TRUNCATED AT 250 WORDS)     

In vitro validation and clinical testing of an indirect calorimetry system for ventilated preterm infants that is unaffected by endotracheal tube leaks and can be used during nasal continuous positive airway pressure

Energy expenditure measurements in ventilated preterm infants are difficult because indirect calorimetry underestimates energy expenditure during gas leaks around uncuffed endotracheal tubes routinely used in preterm infants or during nasal continuous positive airway pressure (CPAP). We, therefore, developed a breath collector that simultaneously sampled expired air expelled at the ventilator outlet and escaping via the tube leak from the infant's mouth and nose. Our breath collector was combined with a proprietary calorimeter (Deltatrac II). In vitro validation was done by methanol burning (VO(2), 13.8 mL/min; VCO(2), 9.2 mL/min) during intermittent positive pressure ventilation (IPPV) with two commonly used ventilators (Sechrist IV-100B and Infant Star). Measurement error was determined at different ventilator flows, peak inspiratory pressures of 12-24 cm H(2)O, and during a complete tube leak. The mean measurement error with both ventilators was low (VO(2) +/- 3 %, VCO(2) +/- 2 %) even during a complete tube leak and did not increase with peak inspiratory pressure. The system response time was 2 min. In vivo measurements at the bedside were performed in 25 preterm infants (body weight, 537-1402 g). Energy expenditure during IPPV was 40 +/- 9 kcal/kg per day and 46 +/- 15 kcal/kg per day during nasal CPAP. The tube leak in the preterm infants studied during IPPV was 0 to 47 %, and during nasal CPAP 84 to 97 %. In conclusion, indirect calorimetry performed with our breath collector was accurate during IPPV and nasal CPAP and was unaffected by tube leaks.     

Validation of doubly labeled water for assessing energy expenditure in infants

Previous studies show that the doubly labeled water method is accurate for measuring energy expenditure in the adult human. To validate this method in infants, carbon dioxide production rate and energy expenditure were measured for 5 to 6 days by doubly labeled water (DLW) and periodic open circuit respiratory gas exchange (RGE) in 10 blinded studies in nine infants following abdominal surgery. Infants were maintained on consistent oral or parenteral nutrition prior to and during study. This avoided diet-related changes in baseline isotopic enrichment of body water which could theoretically contribute to significant errors in calculation of carbon dioxide production rate. For DLW, insensible water loss was assumed to be proportional to respiratory volume and body surface area, where the former was predicted from carbon dioxide production rate. Insensible water loss thus calculated averaged 18% of water turnover. Rates of carbon dioxide production measured by DLW were not significantly different from that of RGE (10.4 +/- 1.1 and 10.5 +/- 0.9 l/kg/day, mean +/- SD, respectively). Energy expenditure was calculated using respiratory quotients from dietary intake (DLW:DIET) and RGE (DLW:RGE) data. There was no significant difference between energy expenditure determined by DLW (DLW:DIET and DLW:RGE) and that measured by RGE (58.5 +/- 6.1, 56.8 +/- 6.1, and 57.3 +/- 5.1 kcal/kg/day, mean +/- SD, respectively). Rate of carbon dioxide production, DLW:diet, and DLW:RGE calculated by DLW differed from corresponding RGE values by -0.9 +/- 6.2, -1.1 +/- 6.1, and 1.6 +/- 6.2%, mean +/- SD, respectively. These findings demonstrate the validity of the doubly labeled water method for determining energy expenditure in infants without concurrent water balance studies.     

Daily metabolic rate in healthy infants

BACKGROUND: Previous estimates of daily metabolic rate in infants were based on short-term unstandardized measurements of energy expenditure (EE). OBJECTIVE: Determine 24-hour metabolic profiles in infants. METHODS: Energy expenditure (kcal/min by indirect calorimetry) and physical activity (oscillations in weight/min/kg body weight) were measured in 10 healthy infants (5.0+/-0.8 months, 68+/-3 cm, 7.3+/-0.8 kg) for 24 hours in the Enhanced Metabolic Testing Activity Chamber while allowing parental interaction. Energy intake, 24-hour EE, resting metabolic rate (RMR), and sleeping metabolic rate (SMR) (kcal/kg/day) were determined. In addition, extrapolated 24-hour EE, RMR, and SMR from the first 4 and 6 hours of data were compared with 24-hour measurements. RESULTS: Twenty-four-hour energy intake, EE, RMR, and SMR (mean+/-SD) were 78.2+/-17.6, 74.7+/-3.8, 65.1+/-3.5, and 60.3+/-3.9, respectively. EE and physical activity showed a decrease at 11:30 pm and a return to daytime levels by 5:30 am, suggesting a metabolic circadian rhythm. Extrapolated 24-hour EE, RMR, and SMR from the first 4 hours (72.2+/-6.6, 65.9+/-8.7, and 64.9+/-6.4) and 6 hours (74.8+/-6.7, 65.8+/-6.6, and 64.8+/-5.6) were similar to 24-hour measurements. CONCLUSIONS: An apparent circadian rhythm in metabolic rate and physical activity was detected by 24-hour measurements. Furthermore, shorter-term measurements of the variables were comparable with 24-hour values.     

A new model for predicting energy requirements of children during catch-up growth developed using doubly labeled water

Energy partitioned to maintenance plus activity, tissue synthesis, and storage was measured in 41 children in early recovery [W/L (wt/length) less than 5th percentile] from severe protein-energy malnutrition and in late recovery (W/L = 25th percentile) to determine energy requirements during catch-up growth. Metabolizable energy intake was measured by bomb calorimetry and metabolic collections. Energy expended (means +/- SD) for maintenance and activity estimated by the doubly labeled water method was 97 +/- 12 kcal/kg FFM (fat-free mass) in early recovery and 98 +/- 12 kcal/kg FFM in late recovery (p greater than 0.5). Energy stored was 5-6 kcal/g of wt gain. Tissue synthesis increased energy expenditure by 1 +/- 0.7 kcal/g gain in both early and late recovery. From these data a mathematical model was developed to predict energy requirements for children during catch-up growth as a function of initial body composition and rate and composition of wt gain. The model for predicting metabolizable energy requirements is [(98 x FFM + A (11.1 B + 2.2 C)], kcal/kg.d, where FFM is fat-free mass expressed as a percentage of body wt, A is wt gain (g/kg.d), B and C are percentage of wt gain/100 as fat and FFM, respectively. The model was tested retrospectively in separate studies of malnourished children.     

Whole body protein turnover measured with 13C-leucine and energy expenditure in preterm infants

Our study was undertaken in preterm infants to examine the relationship of whole body protein kinetics with protein intake and energy expenditure. Leucine kinetics were determined in seven low birth wt preterm infants fed human milk or human milk enriched with protein (2.5 to 4.3 g protein/kg.d). The infants received a short (4-h) constant infusion of L-[1-13C]leucine and leucine turnover and oxidation were calculated from 13C-plasma leucine and expired 13CO2 enrichments measured by mass spectrometry. Energy expenditure was measured by indirect calorimetry. Nonoxidative leucine disposal (an estimate of protein synthesis) and leucine derived from protein (an estimate of protein breakdown) were, respectively, 2.98 +/- 0.82 and 2.06 +/- 0.74 mumol/kg.min. Whole body protein turnover and deposition, derived from leucine kinetics, were 8.22 +/- 2.31 and 2.17 +/- 0.50 g/kg.d, whereas energy expenditure was 56.3 kcal/kg.day. Protein turnover was correlated with protein intake but not with protein deposition. Energy expenditure was correlated with protein turnover, synthesis, and breakdown but not with protein deposition. These data are in agreement with the fact that protein deposition depends upon protein intake, but they also suggest that an elevated protein deposition is not necessarily the result of a rapid protein turnover or associated with an elevated energy expenditure.     

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.