Lipolytic response to metabolic stress in critically ill patients

Objective: To measure whole-body lipolysis and fatty acid re-esterification in critically ill patients. Design: The rates of appearance of glycerol and palmitic acid in blood plasma were measured by infusing stable isotope tracers [²H₅]glycerol and [1-¹³C]palmitic acid, respectively. Energy expenditure was measured by indirect calorimetry. Setting: Medical ICU of The University of Texas Medical Branch Hospital, a university-based referral center. Patients: Five uninjured critically ill patients. Four patients were hospitalized because of respiratory insufficiency and one because of myocardial infarction. Three patients died during their hospitalization. Interventions: Metabolic studies were performed in each patient after an overnight (12-hr) fast. Measurements and Main Results: Mean ± SE glycerol and fatty acid rates of appearance were 4.5 ± 1.0 and 11.5 ± 0.8 μmol/kg·min, respectively. The ratio of fatty acid to glycerol rate of appearance was 2.9 ± 0.5. Resting energy expenditure was 132 ± 6% of predicted. Conclusions: An accelerated rate of lipolysis is part of the metabolic response to severe stress, regardless of its etiology. Because the rate of fatty acid release far exceeded energy requirements, fatty acids that were not oxidized as fuel were re-esterified to triglyceride, presumably in the liver.