Comparison of short term indirect calorimetry and doubly labeled water method for the assessment of energy expenditure in preterm infants

The accuracy of 8-hour indirect calorimetry (IDC) as an estimate of energy expenditure was investigated in 8 healthy preterm infants (birth weight 1,270 +/- 193 g, gestational age 32 +/- 3 weeks, mean +/- SD) in comparison with an analysis over 5 days using the doubly-labeled water (2H2(18)O) method (DLW). The infants that were fed continuously by nasogastric drip with 120 kcal/kg/day of special infant formula were measured twice under thermoneutral conditions in a closed system indirect calorimeter during 8 h with a 4-day interval; simultaneously isotope decay was measured by isotope ratio mass spectrometry in urine samples collected daily during 5 days from 6 h after an oral dose of 2H2(18)O on the first day of IDC, all during the 4th postnatal week. The mean differences between carbon dioxide production rate (rCO2) measured either by single 8-hour IDC or by duplicate 8-hour IDC and the 5-day DLW method, using the two-point analysis or the multipoint analysis were not significantly different from zero. The rCO2 calculated from the DLW method using the two-point analysis differed -1.4 +/- 1.7% from that measured by the multipoint analysis. The mean differences between the metabolic rate estimated from 8 h of IDC and from the 5-day DLW method based on a measured RQ of 0.90 was -6.7 +/- 6.2% and based on the RQ of the feeding -4.5 +/- 6.0%. These differences were not significantly different from zero. We conclude that IDC over 8 h and two-point DLW measurement over 5 days, both methods that can be applied with relative ease in practice, offer an adequate average estimate of energy expenditure in continuously fed preterm infants under thermoneutral conditions.     

Measurement of carbon dioxide production rate in sick ventilated premature infants

A new method is described for measuring the rate of carbon dioxide production, and hence for estimating energy expenditure, in preterm infants receiving assisted ventilation. In a validation study, the mean error in carbon dioxide measurement was 1.9%. Measurements were made, over a 45-min period, on 11 sick, ventilated subjects and carbon dioxide production rate was 5.2 +/- 0.7 (SD) ml/min X kg body weight. We suggest that continuous monitoring of carbon dioxide output will contribute to the clinical assessment of the effects of different ventilator settings on pulmonary gas exchange and that estimated values for energy expenditure will be of value in nutritional studies on sick ventilated infants.     

Application of indirect calorimetry in monitoring feeding of low birth-weight preterm infants

BACKGROUND: We investigated the practical use of indirect calorimetry for the individual nutritional support of preterm infants in order to answer the question whether it is possible to reliably calculate energy expenditure, fat and carbohydrate oxidation in preterm infants individually by using the results of a timed 6-hour-measurement of oxygen consumption and carbon dioxide production. PATIENTS: Measurements were performed in 20 preterm infants (gestational age 30.2 +/- 0.6 weeks, birth weight 1.09 +/- 0.07; mean +/- SEM) at a mean postnatal age of 25 +/- 4 days and with a body weight of 1.35 +/- 0.06 kg. METHODS: Carbon dioxide production (24 h-VCO2), oxygen consumption (24 h-VO2) and respiratory quotient (24 h-RQ) were measured by indirect calorimetry for 24 hours using the Deltatrac II metabolic monitor (Datex, Helsinki, Finland). Additionally, 6 h-VCO2, 6 h-VO2 and 6 h-RQ were determined by measurement over 6 hours. The patients' energy expenditure, fat and carbohydrate oxidation were calculated from VCO2 and VO2 measured over a 24 hour- and 6 hour-period with or without consideration of urinary nitrogen excretion (NU). RESULTS: If NU was not included in the calculation of energy expenditure, the values differed by maximally 1.1% from the calculations including NU. The correlations between the 24 h-RQ and the calculated 24 h-fat or 24 h-carbohydrate oxidation values were statistically significant (r = -0.99; p = 0.0001 and r = 0.773; p = 0.0002 respectively). However, in individual patients, it was not possible to predict 24 h energy expenditure, fat and carbohydrate oxidation of preterm infants using values determined by 6 h indirect calorimetry. CONCLUSION: The determination of the urine-nitrogen excretion is not necessary for calculation of energy expenditure of preterm infants. It is possible to estimate fat and carbohydrate oxidation of preterm infants by the measured 24 h-RQ, but 6 h indirect calorimetry is not accurate enough for calculating the individual nutritional needs of preterm infants in clinical practice. Indirect calorimetry over 24 h may be helpful in the management of selected patients with nutritional problems.     

Effects of intravenous glucose loading on oxygen consumption, carbon dioxide production, and resting energy expenditure in infants with bronchopulmonary dysplasia

To determine the effects of intravenous glucose loading on basal oxygen consumption, resting energy expenditure, and basal carbon dioxide production in infants with bronchopulmonary dysplasia who were still oxygen dependent, we administered intravenous glucose loads of 4 and 12 mg/kg-1/min-1 on 2 consecutive days, under identical experimental conditions, to six infants with bronchopulmonary dysplasia and six healthy control subjects. Infants were not fed for 9 hours before and during the 4- to 6-hour study periods; the intravenous glucose infusion, along with an amino acid mixture (2 gm.kg-1.24 hr-1), was started at the beginning of the fasting period. Oxygen consumption and carbon dioxide production and resting energy expenditure were measured by a flow-through indirect calorimetry technique under basal conditions. Infants with oxygen-dependent bronchopulmonary dysplasia had significantly higher basal oxygen consumption and resting energy expenditure than did control infants and significantly higher basal carbon dioxide production during the high glucose infusion. With glucose loading, infants with bronchopulmonary dysplasia had a significant rise in basal oxygen consumption (7.91 +/- 0.91 ml.kg-1.min-1 to 9.65 +/- 1.35 ml.kg-1.min-1, p less than 0.05), basal carbon dioxide production (5.93 +/- 0.72 ml.kg-1.min-1 to 7.10 +/- 1.04 ml.kg-1.min-1), and resting energy expenditure (53.8 +/- 5.75 kcal.kg-1.24 hr-1 to 65.3 +/- 7.0 kcal.kg-1.24 hr-1, all p values less than 0.05). Control infants had no significant changes with intravenous glucose loading. We conclude that intravenous glucose loading in infants with bronchopulmonary dysplasia resulted in a net increase in resting energy expenditure, which should be taken into account in assessing their energy intake during nutritional management. The risk of pulmonary stress caused by an increase in basal oxygen consumption and carbon dioxide production resulting from glucose load should also be considered.     

Estimation of 24-hour energy expenditure from shorter measurement periods in premature infants

We performed continuous indirect calorimetry for 24 h on nine occasions in small premature infants. Oxygen consumption, carbon dioxide production, respiratory quotient, and energy expenditure were calculated for each 2-h period. The mean energy expenditure during the first 6 h was within 6.5% of the mean for the whole 24-h period in all but one case. The mean error in estimating total daily energy expenditure from 6-h measurements was 0.9%. Because positive and negative errors tend to offset each other, we also calculated the mean absolute error, which was 5.6%. The mean coefficient of variation in energy expenditure among the 2-h periods was 11.0%. The mean coefficients of variation in oxygen consumption, carbon dioxide production, and respiratory quotient were 12.8, 9.9, and 14.1%, respectively. Total daily energy expenditure of small premature infants can be estimated from measurements as short as 6 h with sufficient accuracy for most purposes.     

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.     

Decreased energy expenditure is caused by abnormal body composition in infants with Prader-Willi Syndrome

OBJECTIVE: Infants with Prader-Willi syndrome (PWS) are hypotonic and underweight before the onset of childhood obesity. This study evaluates body composition in the PWS infant and its relationship to energy expenditure. STUDY DESIGN: Sixteen infants and toddlers with PWS (mean age, 12.4+/-6 months; eight female subjects) underwent analysis of body composition with dual-energy x-ray absorptiometry and deuterium dilution, and energy expenditure with both doubly labeled water and indirect calorimetry. RESULTS: Percent body fat was significantly increased (male subjects, P<.001; female subjects, P<.001) and fat-free mass (FFM) was significantly decreased (male subjects, P<.001; female subjects, P=.04) in infants with PWS when compared with age-matched published data for normal infants. Meanwhile, total energy expenditure was significantly decreased (male subjects, P=.025; female subjects, P<.001) in infants with PWS when compared with published normative data. There was a normal relationship between FFM and total energy expenditure in infants with PWS. CONCLUSION: Compared with published data for infants without PWS, infants with PWS demonstrate increased percent body fat, decreased FFM, and decreased energy expenditure. Importantly, total energy expenditure per kilogram of FFM appears similar in infants with and without PWS. We conclude that lower energy expenditure in infants with PWS is caused by decreased FFM.     

An analysis of the variability in estimates of bioenergetic variables in preterm infants

Estimates of average daily energy expenditure and minimal observed oxygen consumption are commonly used to characterize the energy metabolism of neonates. Yet, the errors inherent in these estimates have not been defined. Using measurements of oxygen consumption and carbon dioxide production made in healthy growing low birth weight infants during eight consecutive 3-h interfeeding epochs, we have determined the variability in the mean oxygen consumption, carbon dioxide production, respiratory quotient, total daily energy expenditure, and the minimal observed oxygen consumption among the feeding epochs. The coefficient of variation for oxygen consumption ranged from 3.1 to 9.1%, for minimal observed oxygen consumption from 3.7 to 16.7%, for carbon dioxide production from 3.3 to 7.4%, and for total daily energy expenditure from 2.9 to 7.6%. The SDs for respiratory quotient ranged from 0.008 to 0.066. From these 24-h data we have calculated the error in predicting daily estimates of the mean values for these variables if observations are made for less than 24 h. As expected, this error decreases with increasing duration of observation. These data should prove useful in the design and interpretation of investigations of neonatal energy expenditure.     

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)     

Energy expenditure in infants with congenital heart disease,including a meta-analysis

AIM: To assess energy requirements and body composition in preoperative children with congenital heart disease (CHD). METHODS: In 11 infants with CHD (2-8 mo), total daily energy expenditure (TDEE) and total body water (TBW) were measured with doubly labelled water and compared with historic data from healthy controls. Within the patient group, energy expenditure of infants with versus those without congestive heart failure was compared. Subsequently, the data were pooled with literature data in meta-analyses. RESULTS: CHD patients showed increased TBW (mean +/- SD 66 +/- 3 vs 58 +/- 5% of body weight, p < 0.05) and energy expenditure (381 +/- 42 vs 298 +/- 36 kJ kg(-1) d(-1), p < 0.001). Meta-analyses showed that CHD infants have 35% increased TDEE (376 vs 278 kJ kg(-1) d(-1) , p < 0.00001) and 7% higher TBW (p < 0.0001). Coexistent congestive heart failure (treated with diuretics) had no influence on TDEE (mean difference 14 kJ kg(-1) d(-1) , not significant). In patients with heart failure and growth retardation, an energy balance study showed an average 12% loss of initially ingested energy due to vomiting, increased TDEE and low faecal energy loss, resulting in low energy available for growth, compared with controls (42 +/- 30 vs 96 +/- 61 kJ kg(-1) d(-1) , p < 0.05). CONCLUSION: Many infants with CHD require substantially higher energy intake (at least 100 kJ kg(-1) d(-1) extra) owing to increased TDEE, which is not explained by a higher percentage of body water. Coexistent heart failure does not appear to have an additional influence on TDEE. In infants with CHD and growth failure factors other than elevated TDEE, including vomiting, may explain the disturbed energy balance.     

Respiratory water loss and oxygen consumption in newborn infants during phototherapy

Respiratory water loss was measured together with oxygen consumption (VO2) and carbon dioxide production (VCO2) in 11 full-term and eight preterm infants (mean gestational age 34 weeks, range 31-36 weeks) before and during 1 h of phototherapy. The method for determination of respiratory water loss, VO2 and VCO2 was based on an open flow-through system with a mass spectrometer for measurement of gas concentrations. All infants were studied naked in an incubator with an ambient relative humidity of 50% and with a controlled environment with respect to temperature and air velocity. The infants were calm during the measurements. Before phototherapy, in term infants respiratory water loss was 4.4 (SD 0.7) mg/kg min and VO2 5.9 (0.9) ml/kg min and in preterm infants respiratory water loss was 4.7 (0.8) mg/kg min and VO2 6.1 (0.8) ml/kg min. No significant difference was found between values obtained during or after 1 h of phototherapy and those obtained before.     

Total parenteral nutrition in the newborn infant: energy substrates and respiratory gas exchange

The hypothesis that a high-fat parenteral regimen was beneficial for respiratory gas exchanges, in comparison with a high-glucose regimen, was tested in a paired crossover design. Ten parenterally fed newborn infants with no respiratory problems received two 5-day isoenergetic and isonitrogenous regimens that differed in their nonprotein source of energy; the level of fat intake (low fat (LF) 1 gm.kg-1.day-1; high fat (HF) 3 gm.kg-1.day-1) varied inversely with that of glucose. Continuous transcutaneous PO2 (tcPO2) and PCO2 (tcPCO2), respiratory gas exchange (indirect calorimetry), and plasma arachidonate metabolites were measured at the end of each regimen. Oxygen consumption and resting energy expenditure were not affected by modification of the source of energy. However, carbon dioxide production (VCO2) was higher during LF than during HF (6.9 +/- 0.2 vs 6.2 +/- 0.1 ml.kg-1.min-1; p less than 0.01), as was the respiratory quotient (1.08 +/- 0.02 vs 0.96 +/- 0.02; p less than 0.001). Despite the differences in VCO2, the tcPCO2 was not affected, suggesting adequate pulmonary compensation during LF, as documented by the higher minute ventilation (160 +/- 7 vs 142 +/- 5 ml.kg-1.min-1; p less than 0.01). The lower tcPO2 during the HF regimen (73.8 +/- 2.8 vs 68.8 +/- 2.6 mm Hg; p less than 0.015) indicated a disturbance at the alveolocapillary level induced by the lipid emulsion. No differences were found in circulating levels of prostaglandins and thromboxanes. The substitution of glucose for lipid did not modify fat storage (2.1 +/- 0.3 vs 2.1 +/- 0.3 gm.kg-1.day-1). We conclude that the supposed beneficial effect of a fat emulsion on respiratory gas exchange is questionable.     

Respiratory water loss in fullterm infants on their first day after birth

Measurements of water loss from the airways, oxygen consumption and carbon dioxide production were made in 12 fullterm, newborn infants on their first day after birth, using an open flow-through system. The system includes a mass spectrometer, specially equipped with a water channel, for analysis of gas concentrations. To avoid condensation of water vapour, the tubing in the flow-through system is heated. Respiratory water loss was 4.9 +/- 1.2 (SD) mg/kg min, which meant an insensible water loss from the respiratory tract of 25.4 +/- 6.9 (SD) g per infant and 24 h at rest, at an ambient temperature of 32.2 degrees C and with an ambient humidity of 50%. Oxygen consumption was 6.0 +/- 0.8 (SD) ml/kg min. An inverse relationship was found between respiratory water loss and ambient humidity, with higher losses at a low than at a high humidity. Oxygen consumption did not change very much with ambient humidity.     

Effects of intravenously administered safflower oil emulsion on respiratory gas exchange of low-birth-weight infants

Safflower oil emulsion (Liposyn 10%) was infused intravenously to supplement energy intake in five low-birth-weight infants. Respiratory gas exchange was measured before and after the addition of fat emulsion in doses of 1-2 g of fat/kg/day to an intravenous feeding regimen of dextrose and amino acids. The oxygen consumption and carbon dioxide production rates were greater during fat infusion in all infants, but the mean respiratory quotient was not different. The increase in energy intake provided by the fat emulsion exceeded the increase in energy expenditure, allowing more energy to be stored for growth.     

An indirect calorimetry system for ventilator dependent very low birthweight infants.

With neurodevelopmental outcome of very low birthweight (VLBW) infants being adversely affected by inadequate nutrition during the first few weeks of life, there is an urgent need for more specific nutritional data on the sick VLBW ventilator dependent infant. The development of a new mass spectrometry gas analysis indirect calorimetry system which is non-invasive and can operate over several hours or days is described. Technical evaluation of each of the components of the system indicates a total random error of less than 5%. Systematic error was determined using gas infusions which simulated carbon dioxide production and oxygen consumption. The relative error in the measurement of carbon dioxide production was less than or equal to 1.5% (coefficient of variation (CV) 6.0%)) with carbon dioxide infusion rates ranging from 3.86 to 13.98 ml/min. The relative error in oxygen 'consumption' was less than or equal to 4.3% (CV 2.8%) for infusions of oxygen at rates of 7.5 to 14.80 ml/min. With nitrogen infusions simulating oxygen consumptions of 2.0 and 5.5 ml/min the relative error in the calculated nitrogen infusion was 1.5% (CV 4.1%) and 1.4% (CV 5.7%) respectively. Clinical studies on 10 infants demonstrated a mean energy expenditure of 161.7 kJ/kg/day and a respiratory quotient in excess of 1.0. The energy expenditure of ventilated VLBW infants may be less than previously indicated and the energy mix and nitrogen content of parenteral nutrition regimens recommended for these infants may be inappropriate.     

Energy requirements in Chilean infants

AIM: To evaluate the energy requirements of breast fed infants. METHODS: The study was conducted in 17 healthy exclusively breast fed infants of normal birth weight (mean (SD) 3332 (280) g). Energy expenditure by the doubly labelled water method and milk intake by the dose to infant method were measured at 34 (4) days. A dose of 0. 2 g/kg deuterium oxide (99.8%) and 2.0 g/kg 10% (18)O labelled water was given to the infants, and urine samples were collected for seven consecutive days after dosing. RESULTS: The mean (SD) weight of the infants during the period of evaluation was 4617 (343) g and weight gain 34.0 (7.5) g/day. Daily milk intake was 728 (101) g and its metabolisable energy content 2.71 kJ/g. The energy expenditure of the infants was 1205 (312) kJ/day and energy required for growth was 607 (130) kJ/day. When combined this produced an energy requirement of 391 kJ/kg/day for these infants. CONCLUSION: These data agree with those from other studies in the United Kingdom and the United States and suggest that adequate growth can be achieved with 19.4% less energy than recommended by FAO/WHO/UNU.     

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)     

Day-to-day energy expenditure variability in low birth weight neonates

We estimated the metabolic rate of 13 low birth weight infants over a 9-day period, using indirect calorimetry in conjunction with serial measurements of oxygen consumption, carbon dioxide production, and total urinary nitrogen excretion. The mean percent error for oxygen consumption and carbon dioxide production measurements (determined by alcohol combustion experiments) assignable to the open-circuit system was 0.4 and 3.8%, respectively. Error in the total urinary nitrogen excretion measurement was less than 1% by the Kjeldahl technique. In the clinical setting, however, the range of deviation of measured oxygen consumption, carbon dioxide production and total urinary nitrogen excretion was +/- 12, 12, and 15% of the mean value respectively for an individual patient under standardized controlled conditions. The variability of metabolic rate between infants may be as much as 76%. Factors that had a small effect on metabolic rate were difficult to detect because of the variability inherent in the short-term measurement of metabolic rate. It was virtually impossible to control the sources of variation in the resting metabolism of low birth weight neonates over extended experimental periods. Day-to-day variations in resting energy expenditure may explain, in part, the widely different growth rates of premature infants receiving similar caloric intakes.     

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.     

Respiratory water loss and oxygen consumption in full-term infants exposed to cold air on the first day after birth

Respiratory water loss, oxygen consumption, carbon dioxide production and skin blood flow were measured continuously in nine full-term infants on the first day after birth. After at least 18 min of measurements with the infant asleep in an incubator, with an air temperature of 33°C and a relative humidity of 50%, the temperature of the incubator air was lowered to less than 27.5°C. This resulted in a significant decrease in skin temperature and peripheral skin blood flow, while the infant's core temperature remained unchanged. At the same time, mean respiratory water loss increased from 3.7 to 6.1 mg/kg-min, which can be explained partially by the decrease in ambient humidity that accompanied the decrease in air temperature. In addition, mean oxygen consumption increased from 5.3 to 7.9 ml/kg. min and mean carbon dioxide production increased from 3.8 to 5.9 ml/kg-min. There was no concomitant increase in motor activity. Thus, when the newborn infants were exposed to cool air, they reacted with an increase in respiratory water loss, oxygen consumption and carbon dioxide production before their core temperature was affected and without increasing their motor activity.