Tissue protein synthesis rates in critically ill patients

Objectives: The aims of this study were to simultaneously determine the in vivo rates of protein synthesis in skeletal muscle, peripheral blood lymphocytes, and serum albumin in critically ill patients; to establish whether a relationship between the responses of these tissues could be observed; and to demonstrate if a protein synthesis pattern characteristic of critical illness exists. Design: Descriptive study. Setting: Intensive care unit of a 1000-bed university hospital. Patients: Fifteen patients treated in the intensive care unit. Interventions: None. Measurements and Main Results: Rates of tissue protein syn thesis were determined in vivo once during the course of critical illness, using the flooding method with L-(H-2(5))phenylalanine. Protein synthesis in muscle was 1.49 +/- 0.16%/day; in circulating lymphocytes (i.e., mononuclear cells), protein synthesis was 11.10 +/- 1.82%/day. Albumin synthesis was 12.81 +/- 1.23%/day when expressed as the fractional rate, and was 184 +/- 19 mg/kg/day when expressed as the absolute rate. Conclusions: The individual tissues responded differently to trauma, and showed a wide range of values. The responses were not significantly correlated with each other and no pattern of tissue protein synthesis characteristic of critical illness was observed. However, both muscle protein and albumin synthesis rates correlated with metabolic status and clinical indices of the severity of illness.