Nutrition in chronic critical illness.

Nutritional management of patients with respiratory failure can be a model of nutritional management in chronically critically ill patients. This model requires recognition of the differing metabolic states of starvation and hypermetabolism. Starvation can result in malnutrition, with adverse effect on respiratory muscle strength, ventilatory drive, and immune defense mechanisms. General nutritional goals include preservation of lean body mass by providing adequate energy and positive nitrogen balance. General nutritional prescriptions for both states include a substrate mix of 20% protein, 60% to 70% carbohydrates, and 20% to 30% fat. Positive nitrogen balance is difficult to attain in hypermetabolic patients and energy requirements are increased compared with starved patients. Enteral nutrition should be the mode of initial nutrient delivery unless the gastrointestinal tract is nonfunctional. Monitoring of nutritional support is essential. Complications of nutritional support are multiple. Nutritional hypercapnia is an important complication in a chronically critically ill patient. Outcomes of selected long-term acute patients are poor, with only 8% of patients fully functional 1 year after discharge. Appropriate nutritional therapy is one aspect of management of these patients that has the possibility of optimizing function and survival.