Nutritional and metabolic support: converging concepts

The response to injury and infection can be viewed as a mobilization of body protein, fat, and carbohydrate stores to ensure normal or above-normal circulating levels of substrate in the absence of dietary intake. The situation does not readily yield to nutritional manipulation, and inappropriate nutritional support can cause additional stress. Artificial nutrition is mainly a form of nutrient administration and not nutrient utilization. Modulation of neurohumoral and wound responses to trauma due to starvation and refeeding has not been delineated. The provision of adequate substrates alone does not necessarily guarantee their efficient use in metabolism. With a clear knowledge of the role of cellular mediators in the pathophysiology of disease, it may be possible to develop more rational therapeutic approaches during critical illness. Determination of appropriate and optimal substrate support through parenteral and enteral nutrition remains of great clinical importance. The clinical application of branched-chain amino acids, dispensable amino acids, acetylated amino acids, dipeptides or tripeptides, cysteine, glutamine, and arginine has been explored in recent years. The idea that lipids are deleterious in sepsis and organ failure should be revised and documented, and recent studies suggest that fish oils as a lipid source may also favorably affect immune responses. Under stressful conditions, total parenteral nutrition can require large amounts of energy at a time when there are marked disturbances in glucose utilization. In this area, the use of nonglucose carbohydrates or oligosaccharides can be appropriate, despite the lack of broad acceptance. Existing conventional substrates should be studied beyond mere provision of energy and metabolic pathway support.(ABSTRACT TRUNCATED AT 250 WORDS)