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Metabolic rate and energy balance in infants with bronchopulmonary dysplasia
Metabolic rate and energy balance in infants with bronchopulmonary dysplasia T. F. Yeh, MD, D. A. M c C l e n a n , MD, O. A. Ajayi, MD, a n d R. S. Pildes, MD From the Division of Neonatology, Cook County Children's Hospital and Department of Pediatrics, College of Medicine, University of Illinois, Chicago
To determine energy use and growth of infants with bronchopulmonary dysplasia (BPD), we studied metabolic rate and energy b a l a n c e in five infants with stage lit.IV BPD (birth weight '1309 _ 530 gm, gestational a g e 32 _ 3 weeks, postnatal a g e 5 9 . 8 _ 14.2 days) and in five control infants (birth weight 1540 + 243 gm, gestational a g e 33 +- 2 weeks, postnatal a g e 42.0 +_ 4.2 days). Infants with BPD had significantly lower energy Intake but higher energy expenditure than did control infants. Weight gain and energy cost of growth were significantly less In BPD infants than in control infants, as were urine output and output/intake ratio. We conclude that infants with BPD (4) absorbed caloric intake as well as did normal control infants, (2) had low energy intake and high energy expenditure, resulting in poor weight gain, and (3) had low energy cost of growth, suggesting an alteration in composition of tissue gain, with relatively high water content. (J PEDIATR1989;114:448-51)
Growth failure is a major problem in infants with bronchopulmonary dysplasia, but the cause is unknown. One of the explanations is that these infants have increased energy expenditure because of their mechanical breathing work is at a high level. 1,2 Other causes of growth failure could be chronic hypoxia, emotional deprivation, poor nutritional intake, and poor gastrointestinal absorption2 .4 Infants with BPD often cannot tolerate a large amount of oral feeding because of respiratory distress. These infants are often given restricted amounts of fluid but concentrated formula in an attempt to maintain appropriate caloric intake without fluid overloading. On the basis of this practice, we conducted a study to evaluate the metabolic rate and energy balance in five infants with stage III-IV BPD and to determine their energy use and growth. METHODS Five consecutive infants with stage III-IV BPD and five control infants were studied (Table I). The diagnosis of
Submitted for publication July 5, 1988; accepted Oct. 5, 1988. Reprint requests: T. F. Yeh, MD, Cook County Children's Hospital, 700 South Wood St., Chicago, IL 60612.
448
stage III-IV BPD was based on the criteria of Northway et a12 The five control infants were born prematurely (birth weight and gestational age matched) and had mild, transient respiratory distress shortly after birth but did not require mechanical ventilation. At the time of study, all control infants were more than 5 weeks postnatal age, and none of them had respiratory distress, they were held in the hospital primarily for gaining weight or for social reasons. All BPD infants had moderate to severe respiratory distress shortly after birth and required mechanical ventiBPD Fio2 Vco2 VO~
Bronchopulmonary dysplasia Fraction of inspired oxygen Carbon dioxide production Oxygen consumption
lation for 15 to 120 days. At the time of study, all infants had had their endotracheal tubes removed but still required 02 therapy (FIo2 ranged from 0.35 to 0.60) because of respiratory distress. None of the infants had a patent ductus arteriosus at the time of study. Medications for BPD were withheld for at least 1 week before the start of the study, which was approved by the Cook County Hospital Scientific Committee. Consent for study was obtained in each case.
Volume 114 Number 3
All infants were fed through a nasogastric tube, as tolerated, with whatever they had been fed before the study (Enfamil regular formula, 20 kcai/oz or 24 kcal/oz, in the majority of BPD infants). Daily fluid intake was given through a volumetric infusion pump (Micro FloGrad model 8500, Travenol Labs, Inc., Medical Products Division, Deerfield, Ill.) and was precisely measured. Body weight was measured daily with a scale (Digitron Scale System model 550, International Medical Corp.) that was sensitive to +__l gm of weight chang e. Urine was collected every 8 hours with a U-Bag (Hollister Inc., Libertyville, Ill.) attached to the perineum. During the study, the infant was placed inside a double-walled incubator, and the skin temperature was maintained by servo control at 36.5 ~ C. None of the infants had evidence of infection o r were receiving any medication, including bronchodiiators or furosemide, during the study. Energy balance was studied during the last 2 days of a period of 5 days of static caloric and fluid intake; the daily energy values were obtained by an arithmetic average of the values for the 2 days. Forced feeding to achieve appropriate Caloric requirement Was not done. Instead, the fluid and caloric intakes in BPD infants were prescribed individuallY by the attending physicians, taking into consideration the amount of stomach residue and the respiratory status of the infant. Energy expenditures was determined by indirect calorimetry. The method for continuous measurement of O5 consumption and COs production was based on an opensystem flow-through technique described previously from our nursery. 6,7 The infant's head was placed in a plastic hood through which flowed a constant stream of O2mixture gas (for BPD infant) or air (for normal control subject). This allowed continuous entry of gas into the system while expired gas diluted with air or O2-mixture gas was removed. The mixed expired gas was then sampled, and 02 and CO2 concentration was determined (oxygen analyzer model OM 11 and gas analyzer model LB-2, Beckman Instruments Inc., Schiller Park, Ill.) and continuously recorded (Omni Scribe model B-5000, Houston Instrument, Austin, Texas): To avoid the variability of FI02 of the inspired gas for BPD infants, the 02 mixture gas was first connected to a large reservoir (approximately 60 L) from which a constant flow was drawn to the plastic hood. The total V02 and Vco2 over a given period was determined from the area under the 02 and COs concentration-time curve (AUC) of the mixed expired gas. The AUC was measured by a planimeter (Compensating Polar planimeter, Keuffel & Esser cO., Morristown, N.J.). In this study, V02 and Vc02 were continuously measured for 6 hours, during which the infants received their ongoing nursing care. The total daily V02 and Vco2 values were then extrapolated from those of the 6-hour study period.
M e t a b o l i c rate and energy balance in B P D
Table
449
I. Clinical and biochemical characteristics BPD (n = 5 )
Control
1309 • 530
1540 _ 213
32 +__2
33 _+ 2
(n
= 5)
Birth weight (gin) Gestational age (wk) Postnatal age (days) Weight at time of study (gm) Male/female subjects Respiratory status RDS score
59.8 • 14.2
42.0 • 4.2
2080 • 256
2417 + 297*
2/3
3/2
4.5 • 1.0
Fioz P02 (mm Hg) PCo~ (mm Hg) pH Hematocrit
0.43 50.0 51.4 7.34 37.4
No respiratory distress Room air --
• 0.13 + 8.2 • 4.3 +__0.01 • 6.4
-33.6 • 5.8
Values"aremean +--SD. RDS, Respiratorydistresssyndrome. *p < 0.05.
The total daily energy expenditure was then calculated from daily VO2 and respiratory quotient, assuming the protein metabolism was at 15% of the total caloric values. 8 During calorimetry, the activity of the infant was monitored minute by minute for 5 minutes every 30 minutes by using th e scale developed by Bruck et al. 9 and simplified by Freymond et al) ~ This simplified activity scale monitored movement of the arms, legs, face, and total body regardless of whether the eyes were closed or open. All these activity assessments were performed by the same investigator (D.A.M,). The rate of activity may change from minute to minute, So the highest score of activity observed over the observation period was recorded. The activity score was then expressed as an arithmetic average over the 6-hour study period. Gross energy intake and energy excreted in feces were determined by bomb calorimetry (Parr Instrument Co., Moline, II11).A n aliquot of milk formula and 24-hour stool specimens were collected for heat combustion in a caloric bomb. The digestible energy was calculated from the difference between gross energy intake and energy excreted in feces. Energy storage was calculated from the difference between the digestible energy and the energy expenditure. The energy cost of growth was calculated from the.energy storage and the body weight gain. The amount Of energy excreted in urine was small and was ignored.
450
Yeh et al.
The Journal of Pediatrics March 1989
T a b l e II. Data of energy balance in individual infant
No. of infants BPD 1 2 4 5 Mean _+ SD Control 1 2 3 4 5 Mean _+ SD
Gross energy intake (kcal/ kg/day)
Energy excreted in feces kcal/ kg/day
(%)
106.2 98.2 81.5 96.5 102.8 97.0 -+ 9.5"~
9.4 4.9 10.3 4.3 4.3 6.6_+ 2.6
(8.9) (5.0) (12.3) (4.5) (4.2) (7.0 _+ 3.5)
111.5 107.5 145.5 114.5 149.1 125.6 _+ 19.9
5.6 10.5 11.0 5.3 6.4 7.8 _+ 2.8
(5.0) (10.0) (7.5) (4.6) (4.3) (6.3 _+ 2.4)
Digestible energy (%)
Activity scale
Energy expenditure (kca!/ kg/day)
(91.0) (95.0) (87.7) (94,5) (95.8) (92.8_+3.0)
1.25 0.51 1.20 0.40 0.82 0.85 + 0.34
95.6 68.6 70.0 68.6 69.9 76.0 -+ ll.7t
(95.0) (90.0) (92.5) (95.4) (95.7) (93.7 -+ 2.2)
0.70 0.58 0:80 0.20 0.62. 0.62 -+ 0.22
47.1 62.7 65.7 61.0 56.0 58.5 -+ 7.2
kcal/kg/ day 96.8 93.3 7 1.2 92.2 98.5 90.4 ___9.7"~ 105.9 97.0 134.5 109.2 142.7 117.9 _-_ 17.5
*p < 0.05 (comparisonbetween BPD and controlinfants). ~'p< 0.01.
All data were compared between the BPD and the control infants by means of an independent Student t test. Unless otherwise indicated, the data were expressed as mean z 1 SD.
kg/day, and 0.32 _+ 0.04, respectively). During the study, none of the infants showed deterioration in blood gas values and acid-base balance. DISCUSSION
RESULTS Infants with BPD apparently received significantly (p < 0.01) fewer calories than the control infants (Table II). There was,'however, no significant difference between the groups in energy excretion in feces, in either the absolute'values or in proportion to the gross energy intake. The activity score was comparable between the two groups of infants (0~85 _+ 0.34 vs 0.62 _~ 0.22). As expected. infants with BPD had Significantly (p < 0.01) higher total energy expenditure than cootrol infants (Table II). The average V02 was l 1.0 + 1.9 m l / k g / m i n for BPD patients and 8.3 • 1.0 m g / k g / m i n for control infants (p < 0.01). Energy storage, calculated from digestible energy and energy expenditurel was significantly (p < 0.01) lower in infants with BPD than in control infants. Both groups of infants gained some weight during the study, but the BPD infants gained significantly (p < 0.05) less than the control infants. The energy cost of growth, calculated from energy storage and weight gained, was significantly (p < 0.05) lower in infants with BPD than in the control infants (Table II). Infants with BPD received significantly (p < 0.05) less fluid intake (118.7 • 7.6 ml/kg/day) and had significantly (p < 0.01) lower urine output (26 • 10.8 m l / k g / d a y ) and lower output/intake ratio (0.23 • 0.08) than the control infants (160 • 12.7 ml/kg/day, 51.8 ___ 8.3 ml/
Our study indicated that under the current practice of fluid restrictionl infants with BPD were barely in a state of positive energy balance because of low energy intake and high energy expenditure. Infants with BPD may gain some weight, but the quality of this weight gain may differ from that of normal infants, with relatively higher water content in tissue gained. The Vo2 values in both the control and the BPD infants were higher than those previously reported by others ~," but close to the ,(alues reported by Kurzner et al. 2 The Voz in this study was measured continuously for 6 hours, during which time the infants wer e receiving routine nursing and medical care and their activities were not restricted. The average Vo2 values could therefore be higher than those previously reported,i, 11which measured Vo2 during resting or quiet sleep and for a short period. In our study, measurement was n o t done continuously for 24 hours because a 6-hour period of measurement is sufficient to reflect total daily Vo2) 2 The primary reasons for the growth failure in BPD infants were inadequate caloric intake and excessive energy expenditure. Vohr et al? speculated that infants with BPD might have poor digestion of oral feeding because these infants were often undernourished or receiving prolonged intravenous feeding. The results of our study did not support this speculation; infants with BPD
Volume 114 Number 3
M e t a b o l i c rate and energy balance in B P D
Energy storage (kcal/ kg/day)
Weight gained (gm/kg/ day)
Energy cost of growth (kcal/ 100 gm)
1.2 24.7 1.2 23.6 28.5 14.5 _+ 12.3I"
6.5 8.1 0.6 10.0 10.9 8.8 _+ 1.9"
18 304 201 236 262 205 +_ 128"
58.8 34.3 68.8 48:2 87.7 59.6 ___20.3
13.8 11.0 17.7 14.7 11.1 13.7 + 2.8
426 312 388 328 790 449 • 196
absorbed energy as well as normal infants did. Inadequate caloric intake is a common problem in BPD infants, whose fluid intake is usually restricted because of respiratory distress. The amount of fluid intake in this study was determined by an individual physician on the basis of frequent examinations of the cardiopulmonary status and measurements of both stomach residue and abdominal girth. With this approach, gross energy intake of two infants with BPD'barely met their energy expenditure. Whether an increase of energy intake by other means (e.g., through the parenteral route) or modification of formula composition would affect the energy balance in these infants remains tO be determined. The cause for the increased V02 in infants with BPD is not completely understood but has not been postulated to be related to an increase in the work of breathingJ ~ However, Kao et al. 11showed that an' increase in the work of breathing may contribute only a small proportion of increased V02 in BPD infants. We also monitored activity because it has been our clinical impression that these infants are often very irritable. We did not see any significantlY higher activity score during the 6-hour study period in comparison with the control Scores. In spite of low energy storage, all infants gained some weight during the study. The energy storage per kilogram of weight gain was much lower in BPD infants than in normal infants, suggesting an alteration in the composition of weight gain, with relatively low fat deposition and high fluid content. We also found that the BPD infants had low urine output and low output/intake ratio, suggesting relatively more fluid content in tissue gained. We speculate that the low energy cost of weight gain seen in BPD infants
451
may be merely a reflection of more fluid retention in the tissue gained. Using body weight gain to assess the nutritional status of these infants can thus be misleading. In conclusion, we found that with current feeding practice, infants with stage Ill-IV BPD were barely in a state of positive energy balance, mainly because of their low energy intake and high energy expenditure. S o m e infants with BPD may gai n weight, but the composition Of growing tissue may differ from that of normal infants, with relatively less fat ~tnd more fluid content. Whether parenteral nutritional therapy or modification of feeding formula.would affect the energy storage and tissue composition remains to' be studied. We thank the nursing staff in the special care nursery of their assistance and tolerance. REFERENCES
1. Weinstein MR, Oh W. Oxygen consumption in infants with bronchopulmonary dysplasia. J PEDIATR1981;99:958~61. 2. Kurzner SI, Garg M, Bautista B, Sargen CW, Bowman CM, Keens TGI Growth failure in bronchopulmonary dysplasia: elevated metabolic rates and pulmonary mechanics. J PEDIAIR 1988;112:73-80. 3. Yu VYH, Orgill AA, Lim SB, Bajuk B, Astbury J Growth and development of very low birth weight infants recovering from bronchoptilmonary dysplasia. Arch Dis Child 1983; 58:791-4. 4. Wohr BR, Bell EF, Oh W. Infants with bronchopulmonary dysplasia: growth pattern and neurologic and developmental outcome. Am J Dis Child 1982;136:443~7. 5. Northway WH, Rosan RC, Porter DY. Pulmonary disease following respiratory therapy of hyaline membrane disease: bronchopulmonarydysplasia. N Engl J Med 1967;276:35460. 6. Yeh TF, Lilien LD, Leu ST, Pildes RS. Increased 02 consumption and energy loss in premature infants following medical care procedures. Biol Neonate 1984;46:157-62. 7. Yeh TF. Admani M, Leu ST, Tan M; Pildes RS. Simple daily techniques to calcualte total and interim changes of daily 02 consumption and CO: production m premature infants. Crit Care Med 1982;10:534-8. 8. Karlberg P. Determination of standard energy metabolism (basal metabolism) in normal infants. Acta Pediatr (Stockh) 1952;41:11-21. 9. Bruck K, Parmelee AH, Bruck M. Neutral temperature range and range of "thermal comfort" in premature infants. Biol Neonate 1962:4:32-51. 10. Freymond D, Schultz Y, Decombaz J, Micheli JL, Jequier E. Energy balance, physical activity, and thermogenic effect of feeding in premature infants. Pediatr Res 1986:20:638-45. 11. Kao LC. Durand DJ, Nickerson BG. Improving pulmonary function does not decrease oxygen consumption in infants with bronchopulrnonarydysplas~. J PEDIATR1988;112:61621. 12. Bell DF. Rios GR. Wilmoth PK. Estimation of 24-hour energy expenditure from shorter measurement periods m premature infants. Pediatr Res 1986;20:646-9.
To determine energy use and growth of infants with bronchopulmonary dysplasia (BPD), we studied metabolic rate and energy b a l a n c e in five infants with stage lit.IV BPD (birth weight '1309 _ 530 gm, gestational a g e 32 _ 3 weeks, postnatal a g e 5 9 . 8 _ 14.2 days) and in five control infants (birth weight 1540 + 243 gm, gestational a g e 33 +- 2 weeks, postnatal a g e 42.0 +_ 4.2 days). Infants with BPD had significantly lower energy Intake but higher energy expenditure than did control infants. Weight gain and energy cost of growth were significantly less In BPD infants than in control infants, as were urine output and output/intake ratio. We conclude that infants with BPD (4) absorbed caloric intake as well as did normal control infants, (2) had low energy intake and high energy expenditure, resulting in poor weight gain, and (3) had low energy cost of growth, suggesting an alteration in composition of tissue gain, with relatively high water content. (J PEDIATR1989;114:448-51)
Growth failure is a major problem in infants with bronchopulmonary dysplasia, but the cause is unknown. One of the explanations is that these infants have increased energy expenditure because of their mechanical breathing work is at a high level. 1,2 Other causes of growth failure could be chronic hypoxia, emotional deprivation, poor nutritional intake, and poor gastrointestinal absorption2 .4 Infants with BPD often cannot tolerate a large amount of oral feeding because of respiratory distress. These infants are often given restricted amounts of fluid but concentrated formula in an attempt to maintain appropriate caloric intake without fluid overloading. On the basis of this practice, we conducted a study to evaluate the metabolic rate and energy balance in five infants with stage III-IV BPD and to determine their energy use and growth. METHODS Five consecutive infants with stage III-IV BPD and five control infants were studied (Table I). The diagnosis of
Submitted for publication July 5, 1988; accepted Oct. 5, 1988. Reprint requests: T. F. Yeh, MD, Cook County Children's Hospital, 700 South Wood St., Chicago, IL 60612.
448
stage III-IV BPD was based on the criteria of Northway et a12 The five control infants were born prematurely (birth weight and gestational age matched) and had mild, transient respiratory distress shortly after birth but did not require mechanical ventilation. At the time of study, all control infants were more than 5 weeks postnatal age, and none of them had respiratory distress, they were held in the hospital primarily for gaining weight or for social reasons. All BPD infants had moderate to severe respiratory distress shortly after birth and required mechanical ventiBPD Fio2 Vco2 VO~
Bronchopulmonary dysplasia Fraction of inspired oxygen Carbon dioxide production Oxygen consumption
lation for 15 to 120 days. At the time of study, all infants had had their endotracheal tubes removed but still required 02 therapy (FIo2 ranged from 0.35 to 0.60) because of respiratory distress. None of the infants had a patent ductus arteriosus at the time of study. Medications for BPD were withheld for at least 1 week before the start of the study, which was approved by the Cook County Hospital Scientific Committee. Consent for study was obtained in each case.
Volume 114 Number 3
All infants were fed through a nasogastric tube, as tolerated, with whatever they had been fed before the study (Enfamil regular formula, 20 kcai/oz or 24 kcal/oz, in the majority of BPD infants). Daily fluid intake was given through a volumetric infusion pump (Micro FloGrad model 8500, Travenol Labs, Inc., Medical Products Division, Deerfield, Ill.) and was precisely measured. Body weight was measured daily with a scale (Digitron Scale System model 550, International Medical Corp.) that was sensitive to +__l gm of weight chang e. Urine was collected every 8 hours with a U-Bag (Hollister Inc., Libertyville, Ill.) attached to the perineum. During the study, the infant was placed inside a double-walled incubator, and the skin temperature was maintained by servo control at 36.5 ~ C. None of the infants had evidence of infection o r were receiving any medication, including bronchodiiators or furosemide, during the study. Energy balance was studied during the last 2 days of a period of 5 days of static caloric and fluid intake; the daily energy values were obtained by an arithmetic average of the values for the 2 days. Forced feeding to achieve appropriate Caloric requirement Was not done. Instead, the fluid and caloric intakes in BPD infants were prescribed individuallY by the attending physicians, taking into consideration the amount of stomach residue and the respiratory status of the infant. Energy expenditures was determined by indirect calorimetry. The method for continuous measurement of O5 consumption and COs production was based on an opensystem flow-through technique described previously from our nursery. 6,7 The infant's head was placed in a plastic hood through which flowed a constant stream of O2mixture gas (for BPD infant) or air (for normal control subject). This allowed continuous entry of gas into the system while expired gas diluted with air or O2-mixture gas was removed. The mixed expired gas was then sampled, and 02 and CO2 concentration was determined (oxygen analyzer model OM 11 and gas analyzer model LB-2, Beckman Instruments Inc., Schiller Park, Ill.) and continuously recorded (Omni Scribe model B-5000, Houston Instrument, Austin, Texas): To avoid the variability of FI02 of the inspired gas for BPD infants, the 02 mixture gas was first connected to a large reservoir (approximately 60 L) from which a constant flow was drawn to the plastic hood. The total V02 and Vco2 over a given period was determined from the area under the 02 and COs concentration-time curve (AUC) of the mixed expired gas. The AUC was measured by a planimeter (Compensating Polar planimeter, Keuffel & Esser cO., Morristown, N.J.). In this study, V02 and Vc02 were continuously measured for 6 hours, during which the infants received their ongoing nursing care. The total daily V02 and Vco2 values were then extrapolated from those of the 6-hour study period.
M e t a b o l i c rate and energy balance in B P D
Table
449
I. Clinical and biochemical characteristics BPD (n = 5 )
Control
1309 • 530
1540 _ 213
32 +__2
33 _+ 2
(n
= 5)
Birth weight (gin) Gestational age (wk) Postnatal age (days) Weight at time of study (gm) Male/female subjects Respiratory status RDS score
59.8 • 14.2
42.0 • 4.2
2080 • 256
2417 + 297*
2/3
3/2
4.5 • 1.0
Fioz P02 (mm Hg) PCo~ (mm Hg) pH Hematocrit
0.43 50.0 51.4 7.34 37.4
No respiratory distress Room air --
• 0.13 + 8.2 • 4.3 +__0.01 • 6.4
-33.6 • 5.8
Values"aremean +--SD. RDS, Respiratorydistresssyndrome. *p < 0.05.
The total daily energy expenditure was then calculated from daily VO2 and respiratory quotient, assuming the protein metabolism was at 15% of the total caloric values. 8 During calorimetry, the activity of the infant was monitored minute by minute for 5 minutes every 30 minutes by using th e scale developed by Bruck et al. 9 and simplified by Freymond et al) ~ This simplified activity scale monitored movement of the arms, legs, face, and total body regardless of whether the eyes were closed or open. All these activity assessments were performed by the same investigator (D.A.M,). The rate of activity may change from minute to minute, So the highest score of activity observed over the observation period was recorded. The activity score was then expressed as an arithmetic average over the 6-hour study period. Gross energy intake and energy excreted in feces were determined by bomb calorimetry (Parr Instrument Co., Moline, II11).A n aliquot of milk formula and 24-hour stool specimens were collected for heat combustion in a caloric bomb. The digestible energy was calculated from the difference between gross energy intake and energy excreted in feces. Energy storage was calculated from the difference between the digestible energy and the energy expenditure. The energy cost of growth was calculated from the.energy storage and the body weight gain. The amount Of energy excreted in urine was small and was ignored.
450
Yeh et al.
The Journal of Pediatrics March 1989
T a b l e II. Data of energy balance in individual infant
No. of infants BPD 1 2 4 5 Mean _+ SD Control 1 2 3 4 5 Mean _+ SD
Gross energy intake (kcal/ kg/day)
Energy excreted in feces kcal/ kg/day
(%)
106.2 98.2 81.5 96.5 102.8 97.0 -+ 9.5"~
9.4 4.9 10.3 4.3 4.3 6.6_+ 2.6
(8.9) (5.0) (12.3) (4.5) (4.2) (7.0 _+ 3.5)
111.5 107.5 145.5 114.5 149.1 125.6 _+ 19.9
5.6 10.5 11.0 5.3 6.4 7.8 _+ 2.8
(5.0) (10.0) (7.5) (4.6) (4.3) (6.3 _+ 2.4)
Digestible energy (%)
Activity scale
Energy expenditure (kca!/ kg/day)
(91.0) (95.0) (87.7) (94,5) (95.8) (92.8_+3.0)
1.25 0.51 1.20 0.40 0.82 0.85 + 0.34
95.6 68.6 70.0 68.6 69.9 76.0 -+ ll.7t
(95.0) (90.0) (92.5) (95.4) (95.7) (93.7 -+ 2.2)
0.70 0.58 0:80 0.20 0.62. 0.62 -+ 0.22
47.1 62.7 65.7 61.0 56.0 58.5 -+ 7.2
kcal/kg/ day 96.8 93.3 7 1.2 92.2 98.5 90.4 ___9.7"~ 105.9 97.0 134.5 109.2 142.7 117.9 _-_ 17.5
*p < 0.05 (comparisonbetween BPD and controlinfants). ~'p< 0.01.
All data were compared between the BPD and the control infants by means of an independent Student t test. Unless otherwise indicated, the data were expressed as mean z 1 SD.
kg/day, and 0.32 _+ 0.04, respectively). During the study, none of the infants showed deterioration in blood gas values and acid-base balance. DISCUSSION
RESULTS Infants with BPD apparently received significantly (p < 0.01) fewer calories than the control infants (Table II). There was,'however, no significant difference between the groups in energy excretion in feces, in either the absolute'values or in proportion to the gross energy intake. The activity score was comparable between the two groups of infants (0~85 _+ 0.34 vs 0.62 _~ 0.22). As expected. infants with BPD had Significantly (p < 0.01) higher total energy expenditure than cootrol infants (Table II). The average V02 was l 1.0 + 1.9 m l / k g / m i n for BPD patients and 8.3 • 1.0 m g / k g / m i n for control infants (p < 0.01). Energy storage, calculated from digestible energy and energy expenditurel was significantly (p < 0.01) lower in infants with BPD than in control infants. Both groups of infants gained some weight during the study, but the BPD infants gained significantly (p < 0.05) less than the control infants. The energy cost of growth, calculated from energy storage and weight gained, was significantly (p < 0.05) lower in infants with BPD than in the control infants (Table II). Infants with BPD received significantly (p < 0.05) less fluid intake (118.7 • 7.6 ml/kg/day) and had significantly (p < 0.01) lower urine output (26 • 10.8 m l / k g / d a y ) and lower output/intake ratio (0.23 • 0.08) than the control infants (160 • 12.7 ml/kg/day, 51.8 ___ 8.3 ml/
Our study indicated that under the current practice of fluid restrictionl infants with BPD were barely in a state of positive energy balance because of low energy intake and high energy expenditure. Infants with BPD may gain some weight, but the quality of this weight gain may differ from that of normal infants, with relatively higher water content in tissue gained. The Vo2 values in both the control and the BPD infants were higher than those previously reported by others ~," but close to the ,(alues reported by Kurzner et al. 2 The Voz in this study was measured continuously for 6 hours, during which time the infants wer e receiving routine nursing and medical care and their activities were not restricted. The average Vo2 values could therefore be higher than those previously reported,i, 11which measured Vo2 during resting or quiet sleep and for a short period. In our study, measurement was n o t done continuously for 24 hours because a 6-hour period of measurement is sufficient to reflect total daily Vo2) 2 The primary reasons for the growth failure in BPD infants were inadequate caloric intake and excessive energy expenditure. Vohr et al? speculated that infants with BPD might have poor digestion of oral feeding because these infants were often undernourished or receiving prolonged intravenous feeding. The results of our study did not support this speculation; infants with BPD
Volume 114 Number 3
M e t a b o l i c rate and energy balance in B P D
Energy storage (kcal/ kg/day)
Weight gained (gm/kg/ day)
Energy cost of growth (kcal/ 100 gm)
1.2 24.7 1.2 23.6 28.5 14.5 _+ 12.3I"
6.5 8.1 0.6 10.0 10.9 8.8 _+ 1.9"
18 304 201 236 262 205 +_ 128"
58.8 34.3 68.8 48:2 87.7 59.6 ___20.3
13.8 11.0 17.7 14.7 11.1 13.7 + 2.8
426 312 388 328 790 449 • 196
absorbed energy as well as normal infants did. Inadequate caloric intake is a common problem in BPD infants, whose fluid intake is usually restricted because of respiratory distress. The amount of fluid intake in this study was determined by an individual physician on the basis of frequent examinations of the cardiopulmonary status and measurements of both stomach residue and abdominal girth. With this approach, gross energy intake of two infants with BPD'barely met their energy expenditure. Whether an increase of energy intake by other means (e.g., through the parenteral route) or modification of formula composition would affect the energy balance in these infants remains tO be determined. The cause for the increased V02 in infants with BPD is not completely understood but has not been postulated to be related to an increase in the work of breathingJ ~ However, Kao et al. 11showed that an' increase in the work of breathing may contribute only a small proportion of increased V02 in BPD infants. We also monitored activity because it has been our clinical impression that these infants are often very irritable. We did not see any significantlY higher activity score during the 6-hour study period in comparison with the control Scores. In spite of low energy storage, all infants gained some weight during the study. The energy storage per kilogram of weight gain was much lower in BPD infants than in normal infants, suggesting an alteration in the composition of weight gain, with relatively low fat deposition and high fluid content. We also found that the BPD infants had low urine output and low output/intake ratio, suggesting relatively more fluid content in tissue gained. We speculate that the low energy cost of weight gain seen in BPD infants
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may be merely a reflection of more fluid retention in the tissue gained. Using body weight gain to assess the nutritional status of these infants can thus be misleading. In conclusion, we found that with current feeding practice, infants with stage Ill-IV BPD were barely in a state of positive energy balance, mainly because of their low energy intake and high energy expenditure. S o m e infants with BPD may gai n weight, but the composition Of growing tissue may differ from that of normal infants, with relatively less fat ~tnd more fluid content. Whether parenteral nutritional therapy or modification of feeding formula.would affect the energy storage and tissue composition remains to' be studied. We thank the nursing staff in the special care nursery of their assistance and tolerance. REFERENCES
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