Impact of Early Parenteral Nutrition on Muscle and Adipose Tissue Compartments During Critical Illness

Objective: The goal of enhanced nutrition in critically ill patients is to improve outcome by reducing lean tissue wasting. However, such effect has not been proven. This study aimed to assess the effect of early administration of parenteral nutrition on muscle volume and composition by repeated quantitative CT. Design: A preplanned substudy of a randomized controlled trial (Early Parenteral Nutrition Completing Enteral Nutrition in Adult Critically Ill Patients [EPaNIC]), which compared early initiation of parenteral nutrition when enteral nutrition was insufficient (early parenteral nutrition) with tolerating a pronounced nutritional deficit for 1 week in ICU (late parenteral nutrition). Late parenteral nutrition prevented infections and accelerated recovery. Setting: University hospital. Patients: Fifteen EPaNIC study neurosurgical patients requiring prescheduled repeated follow-up CT scans and six healthy volunteers matched for age, gender, and body mass index. Intervention: Repeated abdominal and femoral quantitative CT images were obtained in a standardized manner on median ICU day 2 (interquartile range, 2-3) and day 9 (interquartile range, 8-10). Intramuscular, subcutaneous, and visceral fat compartments were delineated manually. Muscle and adipose tissue volume and composition were quantified using standard Hounsfield Unit ranges. Measurements and Main Results: Critical illness evoked substantial loss of femoral muscle volume in 1 week's time, irrespective of the nutritional regimen. Early parenteral nutrition reduced the quality of the muscle tissue, as reflected by the attenuation, revealing increased intramuscular water/lipid content. Early parenteral nutrition also increased the volume of adipose tissue islets within the femoral muscle compartment. These changes in skeletal muscle quality correlated with caloric intake. In the abdominal muscle compartments, changes were similar, albeit smaller. Femoral and abdominal subcutaneous adipose tissue compartments were unaffected by disease and nutritional strategy. Conclusions: Early parenteral nutrition did not prevent the pronounced wasting of skeletal muscle observed over the first week of critical illness. Furthermore, early parenteral nutrition increased the amount of adipose tissue within the muscle compartments.