Indirect calorimetry in the ICU

Critically-ill patients have unpredictable and dynamic metabolic demands that are difficult to predict and quantify. Combined with the high incidence of pre-existing or development of malnutrition in the ICU, these metabolic demands have deleterious effects on outcomes when patients are provided with inadequate or inappropriate nutrition support. Providing adequate nutritional support that meets these varying metabolic demands is a long-standing challenge in the intensive care unit (ICU). Indirect calorimetry (ICal) is a tool that allows ICU practitioners to accurately assess energy expenditure (EE) in critically-ill patients with unpredictable metabolic demands to optimize nutrition support. ICal provides clinicians with a patient’s measured EE (MEE), a quantification of cellular metabolism, and respiratory quotient (RQ), a reflection of which substrates are primarily being utilized for fuel. Study results help clinicians target optimal nutritional goals and prevent adverse effects associated with both under- and overfeeding patients. Recent studies have suggested avoiding caloric deficits and providing tight caloric control may improve morbidity and mortality outcomes in critically-ill patients, though more studies are needed to verify this potential benefit. Currently, there are no specific guideline recommendations to help clinicians utilize ICal in the ICU. Although ICal is considered to be the gold standard for determining EE in critically-ill patients, its use remains limited by availability, cost, and the need for trained personnel for correct use.