Protein metabolism is a dynamic process in which protein is synthesized and degraded continuously from exogenous and endogenous amino acids. Although expensive in terms of amino acids and energy, this system permits rapid shifts from one protein pool to another at appropriate times so that the vast array of functions performed by proteins can be carried out by a pool of finite size. High priority proteins essential for survival are maintained or expanded at the expense of low priority reservoirs, permitting survival during periods of starvation or stress. When the demand for expansion of certain protein pools is excessive (severe trauma), when endogenous amino acid reservoirs are depleted (prolonged starvation), or when regulatory mechanisms for efficient utilization are disordered (as in sepsis), those proteins essential for survival become depleted and death ensues. The goal of nutritional support is to provide exogenous nutrients to prevent this downward spiral. Greater understanding of specific alterations in protein metabolism may permit more effective tailoring of amino acid profiles for specific diseases states (as branch chain amino acids in sepsis). These are discussed in detail in appropriate articles, but the underlying principle of nutritional support to preserve essential high priority proteins is the unifying concept of nutritional support of the surgical patients.
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