Abstract
Extract: It seemed desirable and interesting to study the total energy expended during a period of several hours under conditions most commonly encountered under different infant care practices.
The investigations were carried out on a total of 23 premature infants with a birth weight ranging from 1100 to 2120 g and aged from 2 to 31 days. Oxygen consumption was measured by an open circuit method using the Kipp diaferometer. Using three thermal conditions, measurements were started when four hours had elapsed after the last feed. Physical activity was observed and recorded continuously by an arbitrary method. The basal metabolic rate and the metabolic response to cold subtracted from the total metabolism measured under different experimental conditions gave the combined number of calories produced by specific dynamic action and physical activity. The information obtained from a previous study on specific dynamic action made it possible to approximate the calorigenic effect of food in the four series of examinations reported.
Details of the studies carried out on premature infants while receiving human milk and kept in incubators with temperature maintained between 33–36° are shown in table I. In addition to the basal metabolic rate, total heat production observed throughout the observational period, calculated total daily heat production, and the percentage distribution of times spent in sleep and in physical activity with various intensity are also listed. The average total heat production observed exceeds the minimal metabolic rate by 9.8 kcal/kg/24 h per subject. If allowance is made for the specific dynamic action expected from the average daily intake of human milk (1.1 g protein/ml) 3.0 kcal/kg/24 h can be attributed to muscular activity. The magnitude of this component of the total energy expenditure is consistent with the markedly reduced physical activity exhibited by premature infants maintained in a thermally neutral environment.
The results obtained on premature infants receiving an artificial formula containing 3.43% protein are listed in table II and shown diagrammatically in figure 1. The total daily caloric output averages 55.0 kcal/kg/24 h, a value roughly 39% above the basal rate, in contrast to the average increase of 25% observed in breast milk-fed infants. This difference in the combined quota of specific dynamic action and physical activity (8.8 and 15.3 kcal/kg/24 h, respectively) is due partly to the higher protein and caloric intake, and partly to the lesser proportion of time spent in deep sleep.
Table III summarizes the results of studies of the energy exchange of five swaddled premature infants kept at a room temperature of 20–22°. It can be seen that the total daily heat production averages 58.3 kcal/kg/24 h, which is not appreciably greater than that observed in Adapta-fed infants maintained at neutral temperature. The extra calories above the basal amount to 18.6 kcal/kg/24 h, representing a 47 % rise above the minimal rate. This amount of heat includes not only the specific dynamic action and the activity quota, but also thermoregulatory heat production. The metabolic response to cold amounts roughly to 10 kcal/kg/24 h. The remaining extra calories above those required for basal heat production are partitioned between specific dynamic action and physical activity; this distribution is consistent with the proportion of times spent sleeping and with activity of various intensity. It is also consistent with the observation that the calorigenic effect of food manifests itself as an additional amount of heat in a heat-losing environment.
Table IV presents the observations made on six premature infants kept unclothed at 28–29°. The total daily energy expenditure, almost 100% above that of basal heat production, averaged 80 kcal/kg: 41.3 for basal metabolism; 15.3 for chemical heat regulation without gross, visible muscular activity; 7.3 for specific dynamic action; and 16.1 for activity. The relative proportion of these components is shown in figure 3. The magnitude of the activity quota is readily explained by the percentage of time spent awake while displaying periodically increasing struggling and restless crying.
Speculation: The results obtained have much bearing on the feeding of premature infants. It appears important to reevaluate the caloric needs for maintenance at neutral temperatures, since it has become increasingly accepted that the majority of small premature infants should be cared for under neutral thermal conditions. The observations suggest, in addition to the caloric need for maintenance, that the total caloric requirements are considerably lower than the widely employed figures used to approximate the caloric need of premature infants. Hence, the desirability of extending such studies to include the total caloric requirement is quite obvious. It would be most interesting to complete our knowledge concerning the adequacy and physiological basis of the caloric feeding of premature infants cared for under different thermal conditions.
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Mestyán, J., Járai, I. & Fekete, M. The Total Energy Expenditure and its Components in Premature Infants Maintained under Different Nursing and Environmental Conditions. Pediatr Res 2, 161–171 (1968). https://doi.org/10.1203/00006450-196805000-00002
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DOI: https://doi.org/10.1203/00006450-196805000-00002
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