Energy Reserves and Requirements
Posted by Surgery on Aug 8, 2008
The neonate and child differ significantly from the adult patient in the proportion of available metabolic reserves. Table 8-1 outlines the macronutrient reserves of the neonate, child, and adult in percentage of total body weight (14,15,16). Carbohydrate stores are limited in all age groups and afford only acute provisions when necessary. Lipid reserves, an important and efficient source of energy, are reduced in the neonate as compared with the adult and gradually increase with age. The most striking difference between the adult and pediatric patient is the quantity of stored protein. The protein reserve of the adult is nearly twice that of the neonate.
Along with lower metabolic reserves, neonates and children share much higher baseline energy requirements. Studies have consistently demonstrated that the resting energy expenditure for neonates is two to three times that of adults when standardized for body weight (17,18,19). Clearly, the child’s rapid growth and cellular differentiation heavily influence the magnitude of the corresponding energy metabolism. In addition, the relationship between increased energy expenditure and decreased body weight is conserved throughout mammalian species. This may be related to the increased body surface area and possibly a higher brain-to-body mass ratio.Basic protein and energy requirements for the neonate, child, and adult based on recommendations by the National Academy of Sciences are compared in Table 8-2 (20). The protein needs of the neonate are almost three times that of the healthy adult. In premature infants, a minimum protein allotment of 2.8 g per kg per day is required to maintain in utero growth rates (21). Thus, with both increased metabolic demand and limited substrate reserve, the child has the significant potential for profound nutritional deficiency in settings of critical illness and injury.
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