Conditionspecific Nutritionals Hypermetabolic Stress or Trauma

Severe injury causes abrupt changes in metabolism. Critically ill patients experience a metabolic response to injury that is divided into what is known as an ebb phase and a flow phase (9). During the ebb phase, blood pressure, cardiac output, body temperature, and oxygen consumption are reduced, usually in conjunction with hemorrhage. This depression in metabolic rate may be a protective mechanism during this period of hemodynamic instability.

As blood volume stabilizes, the ebb phase is replaced by the flow phase. The acute response is a hypermetabolic state characterized by increased cardiac output and urinary nitrogen losses, altered glucose metabolism, and accelerated catabolism. Levels of the catabolic stress hormones, glucocorticoids (10,11), glucagon (12-14), and catecholamines (15-16) are increased. These hormonal conditions favor the breakdown of muscle tissue to provide amino acids for gluconeogenesis and hepatic protein synthesis. The physiologic consequence is a rapid loss of nitrogen and lean body tissue after severe injury. The levels of catabolic hormones decrease gradually during the adaptive flow phase. Recovery continues throughout this response, which is associated with the predominance of anabolic processes such as wound healing.

Historically, parenteral nutrition predominated in the care of critically ill patients because of the routine availability of central venous access and standardized techniques. Health care professionals preferred parenteral nutrition because it bypassed the GI tract, which they assumed to be totally dysfunctional in the critically ill. However, evidence indicates that enteral nutrition support confers benefits not seen with parenteral nutrition such as reduced incidence of infection and maintenance of gut structure and function. As a result, clinicians are increasingly advocating tube feeding for critically ill patients, whenever possible.

Recent nutrition research has focused on the clinical benefits of enterally feeding hypermetabolic patients. Several trials have reported significant decreases in infections and/or wound healing complications (17-20), hospital length of stay (17,20,21), and multiple organ failure (19) in patients fed specialized enteral formulas compared with patients fed standard enteral formulas. These specialized enteral formulas contain ingredients shown to enhance the immune response, improve wound healing, reduce free radical formation, and alter the inflammatory response. Included are the amino acids arginine (22) and glutamine (23) as conditionally essential nutrients during trauma, omega-3 fatty acids (24), and antioxidants (25-27).

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