Factors affecting the measurement of energy expenditure during energy balance studies in preterm infants

The indirect calorimetry in very low birth weight preterm infants: An easier and reliable procedure

OBJECTIVES

Preterm infants are at increased risk of developing extrauterine growth restriction, which is associated with worse health outcomes. The energy needs are not well known, as the measurement of resting energy expenditure (REE) using indirect calorimetry has critical issues when applied to infants. One of the main issues is the time required to obtain reliable data owing to the difficulty in keeping infants quiet during the entire examination. Thus, the aim of this study was to define the minimum duration of calorimetry to obtain reliable data.

METHODS

The volume of oxygen consumption (VO₂) and the volume of carbon dioxide production (VCO₂) were recorded for a mean duration of 90 consecutive minutes. REE was calculated using a neonatal prototype calculator. We extracted data regarding VO₂, VCO₂, and REE at 10(T1), 20(T2), 30(T3), 40(T4), and 50(T5) minutes of steady state and compared these data to those of entire steady state period.

RESULTS

Twenty-six very low birth weight preterm infants were evaluated at 36.58 ± 0.99 wk corrected age. Infants were appropriate for gestational age and clinically stable without comorbidities. There were no significant differences between mean VO₂ and REE at T1 (8.26 ± 1.45 mL/kg to 57.80 ± 10.51 kcal/kg), T2 (8.15 ± 1.41 mL/kg to 56.87 ± 10.05 kcal/kg), T3 (8.04 ± 1.41 mL/kg to 56.32 ± 9.73 kcal/kg), T4 (8.05 ± 1.41 mL/kg to 56.07 ± 10.28 kcal/kg), and T5 (8.06 ± 1.55 mL/kg to 57.17 ± 11.62 kcal/kg), respectively, compared to steady state (8.13 ± 1.33 mL/kg to 56.77 ± 9.34 kcal/kg). The median values of VCO₂ were significantly different only when T1 data were compared with other time slots (7.02 ± 1.02 mL/kg at steady state; 7.26 ± 1.23 mL/kg at T1; 7.13 ± 1.20 mL/kg at T2; 7.02 ± 1.19 mL/kg at T3; 6.85 ± 1.16 mL/kg at T4; 6.91 ± 1.24 mL/kg at T5).

CONCLUSION

Twenty consecutive minutes in steady state condition are sufficient to obtain reliable data on REE in stable, very low birth weight infants.

Exploration of the Contribution of Biobehavioral Variables to the Energy Expenditure of Preterm Infants

Variation in energy expended by preterm infants may be due to infant maturity and history of resolved acute lung disease (respiratory distress syndrome [RDS]) as well as growth, caloric intake, and activity. Indirect calorimetry was used in this exploratory, short-term longitudinal study to estimate energy expenditure (EE) from measures of inspired and expired O2 and CO2 .The sample included 35 assessments for 10 preterm infants (5 with and 5 without RDS history). Lung disease history (resolved RDS, no RDS diagnosis), weight gain (g/d) from the day on which birth weight had been regained to the study day, mean activity level, the number of the assessment (1 6), and the interaction of lung disease history and time were included in a linear mixed model for repeated measures. Time was an index of postconceptional and postnatal age; all 3 were highly correlated. Because of high correlation with weight gain, caloric intake was not included in the analytic model. Lung disease history, mean activity level, and time were significant contributors to EE. A more precise measure of medical status than absence or presence of lung disease history, evenly spaced repetitions of EE assessment, and exploration of contexts in which the infants exhibit a higher activity level are needed in a replication study with a larger sample.

Relationship between energy expenditure and stress behaviors of preterm infants in the neonatal intensive care unit

PURPOSE

This research evaluated the relationship between behaviors and energy expenditure in preterm infants receiving nursing interventions.

DESIGN AND METHODS

This study was an explorative secondary data analysis from a previous study. The current study investigated energy expenditure calculated using heart rate-based energy expenditure-estimate across 500 repeated measures for 37 infants.

RESULTS

Research results indicate that preterm infants expend more energy when they show the following seven behaviors: grimace, sucking, diffusion squirm, fist, gape face, salute, and sneezing.

PRACTICE IMPLICATIONS

The interventions for preterm infants should be flexible, according to the infant's stress behaviors and conditions of energy expenditure.

Circadian variation on oxygen consumption in preterm infants

OBJECTIVE

We investigated the diurnal variation in oxygen consumption to determine the optimal time periods of calorimetry in preterm infants.

METHODS

Oxygen consumption (VO(2)) was measured continuously for 24 h using indirect calorimetry. Twenty-two premature infants with gestational age of 27-31 (31+/-1.7) weeks were enrolled in the study. Heart rate, respiratory rate, oxygen saturation, skin and rectal temperature and physical activity were monitored continuously.

RESULTS

The averaged values of VO(2) showed a significant pattern (P<0.0001) of circadian rhythm with a peak in the afternoon and a nadir during the night with significantly differences between the mean VO(2) values. A circadian variation of VO(2) was found in more than 80% of preterm infants and was unrelated to gestational age, physical activity or environmental stress. The infants spent 90.4% of their time sleeping.

CONCLUSIONS

These findings indicate the possible existence of an endogenous circadian rhythm of VO(2) in preterm infants beginning shortly after birth. Day-night variations of VO(2) should be considered when VO(2) values are extrapolated from short measurement periods to prevent overestimation of values.

Determining the least time required for measuring energy expenditure in premature neonates

OBJECTIVE

To compare O2 consumption, CO2 production, respiratory quotient and resting metabolic rate in premature neonates measured for 5 and 10 min steady-state periods and 15 and 20 min non-steady-state periods versus a 2-h measurement period.

METHODS

A prospective study with neonates evaluated by indirect calorimetry. The measurements from the 5, 10, 15, and 20 min periods were taken based on the printout data from the IC monitor at an interval of 1 h before the beginning feeding and were contained in the 2-h measurement. The 5- and 10-min measurements followed the steady-state criterion.

RESULTS

We evaluated 35 premature neonates appropriate for gestational age (born at 28-34 weeks' gestation). Mean age was 20 days+/-9 (median 14 days) and mean weight was 1530+/-270 g (median 1510 g). There was no statistically significant difference between mean VO2, VCO2, respiratory quotient and energy expenditure at 5, 10, 15, and 20 min and 2 h.

CONCLUSIONS

The 5 and 10 min steady-state measurements or a measurement of more than 15 min without reaching steady state produce results similar to those of 2 h measurements.

Longitudinal study of energy expenditure in preterm neonates <30 weeks' gestation during the first three postnatal weeks

OBJECTIVES

The objective of this study was to measure energy expenditure (EE) in a contemporary population of preterm neonates <30 weeks' gestation.

STUDY DESIGN

Prospective longitudinal cohort study in 26 consecutive preterm neonates (gestational age, 27 weeks [23-29] [median, range]; birth weight, 980 g [554-1592]). EE was measured by indirect calorimetry on postnatal days 1, 3, 5, 10, and 21. Data on body weight, energy intake, and medical therapy were prospectively collected.

RESULTS

EE increased from 121 +/- 25 kJ/kg per day (29 +/- 6 kcal/kg per day) (mean +/- SD) on day 1 to 222 +/- 25 kJ/kg per day (53 +/- 6 kcal/kg per day) on day 21. An energy deficit occurred only on day 1. EE was closely related to energy intake: For each additional kJ given, EE increased by 0.3 kJ (r = 0.789, P <.0001). Neonates with a birth weight <1000 g did not have a more pronounced energy deficit than the heavier neonates. EE during nasal continuous positive airway pressure in the first postnatal week was 25% lower than during spontaneous respiration.

CONCLUSIONS

EE could be predicted from energy intake with acceptable accuracy in preterm neonates <30 weeks' gestation during the first 3 postnatal weeks. There was no prolonged energy deficit.

Longitudinal evaluation of energy expenditure in preterm infants with birth weight less than 1000 g

The aim of the present study was to obtain serial values of O2 consumption (VO2), CO2 production (VCO2) and energy expenditure (EE) in healthy but extremely-low-birth-weight infants (birth weight <1000 g), during the first 5 weeks after birth. A total of seventeen spontaneously breathing and appropriate-for-gestational-age (birth weight and body length above the 10th and below the 90th percentile) preterm infants with gestational age 25-28 weeks and birth weight 590-990 g were enrolled in the study. Calorimetry was performed using an open-circuit calorimeter on days 6, 12, 18, 24, 30 and 36 of postnatal life. During the 5 weeks of observation, VO2 increased from 4.7 (SD 0.5) to 9.1 (SD 1.0) ml/kg per min, VCO2 from 4.5 (SD 0.4) to 8.3 (SD 0.6) ml/kg per min and EE from 115 (SD 12) to 310 (SD 71) kJ/kg per d. The energy intake was always higher than EE, even at days 6 and 12. The RER decreased from 0.99 (SD 0.09) at day 12 to 0.91 (SD 0.05) at day 30. On all study days, there were highly significant positive correlations between energy intake and weight gain, EE and weight gain, and EE and energy intake (P<0.05). Multiple regression analysis showed that on most study days EE was more affected by energy intake than by weight gain. We conclude that in healthy preterm infants with birth weight <1000 g, EE increases by about 150 % in the first 5 weeks after birth, and that the EE values are related to energy intake and weight gain independent of postnatal age.