is almost three times that of the healthy adult. In premature infants, a minimum protein allotment of 2.8 g/kg/d is required to maintain in utero growth rates.10 Together, the increased metabolic demand and limited nutrient reserves of the infant mandate early nutritional support in times of traumatic injury and critical illness.

Micronutrients are also important for normal growth and development. Vitamins and trace elements are needed for vital enzymatic reactions, and if not available in the child's regular diet, they should be supplemented to meet the recommended daily reference intake (Table 13.3). However, because these micronutrients are not consumed by the biochemical reactions for which they are required, providing excessive amounts in times of physiologic stress is not necessary and, in fact, may lead to toxicity.

The Nutritional Management of the Critically Ill Child

Children undergo profound yet predictable changes in metabolism with the onset and continuation of critical illness. The turnover rates of all nutrients increase substantially, and net protein breakdown is greatly accelerated. Despite a modest increase in protein synthesis, net protein balance (the difference between protein synthesis and protein degradation) is considerably negative. Muscle protein is broken down, and amino acids are sent to the liver for conversion into acutely needed inflammatory mediators and acute phase reactants. The remaining amino acids are used to manufacture glucose through the process of gluconeogenesis to supply a diverse array of tissues. Although these changes represent excellent short-term adaptations in the child, the metabolic stress response can become injurious if left unrestrained, as it depletes body protein stores, dampens growth, and may contribute to multiple organ failure.

Protein Metabolism

At baseline, infants are known to have higher rates of protein turnover than adults, and even greater rates of protein turnover have been measured in premature and low birth weight infants.11 Extremely low birth weight infants receiving no dietary protein can lose in excess of 1.2 g/kg/d of endogenous protein.12 Although the healthy adult can subsist with a neutral protein balance, infants must maintain a positive protein balance to attain adequate growth and development.

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