Metabolic Measurements in the Critically Ill

Critical illness is associated with major abnormalities in metabolism. The “metabolic response to stress” characterized by changes in metabolic rate, altered substrate utilization and catabolism, provides a challenge when designing nutritional support regimens. This has increased interest in measuring the metabolic rate and substrate utilization to provide a better understanding of how, when, and what to feed critically ill patients. In critically ill patients metabolic rate can be determined from measurements of oxygen consumption and carbon dioxide production. Mechanical ventilation, with its elevated oxygen concentrations and airway pressures and abnormal respiratory patterns, presents a challenging environment in which to make these measurements.