Nutrition and respiratory disease.

Correlations between nutritional status and respiratory function, effects of nutritional substrates on respiration, and optimal nutritional support during respiratory failure are reviewed. Somatic protein depletion is common in patients with either acute respiratory failure or chronic obstructive pulmonary disease. The etiology of the malnutrition includes decreased nutrient intake, increased work of breathing, and increased metabolic rate caused by infections. Excessive administration of glucose or protein can have detrimental effects on respiratory status. Weaning patients from ventilators may be prolonged or even impossible secondary to increased carbon dioxide production in patients receiving high caloric loads of glucose. Excessive protein administration stimulates ventilatory drive and can be detrimental in patients who cannot increase their minute ventilation. Fat is the preferred substrate for energy in selected mechanically ventilated patients requiring total parenteral nutrition because it is oxidized at a lower respiratory quotient than glucose. Measurements of respiratory quotient, oxygen consumption, and carbon dioxide production can be useful in providing optimal nutritional support to the patient with respiratory compromise.