title: Whole body protein kinetics during hypocaloric and normocaloric feeding in critically ill patients.
abstract: BACKGROUND
  Optimal feeding of critically ill patients in the ICU is controversial. Existing guidelines rest on rather weak evidence. Whole body protein kinetics may be an attractive technique for assessing optimal protein intake. In this study, critically ill patients were investigated during hypocaloric and normocaloric IV nutrition.
  
  
  METHODS
  Neurosurgical patients on mechanical ventilation (n = 16) were studied during a 48-hour period. In random order 50% and 100% of measured energy expenditure was given as IV nutrition during 24 hours, corresponding to hypocaloric and normocaloric nutrition, respectively. At the end of each period, whole body protein turnover was measured using d5-phenylalanine and 13C-leucine tracers.
  
  
  RESULTS
  The phenylalanine tracer indicated that whole-body protein synthesis was lower during hypocaloric feeding, while whole-body protein degradation and amino acid oxidation were unaltered, which resulted in a more negative protein balance, namely -1.9 ± 2.1 versus -0.7 ± 1.3 mg phenylalanine/kg/h (P = 0.014). The leucine tracer indicated that whole body protein synthesis and degradation and amino acid oxidation were unaltered, but the protein balance was negative during hypocaloric feeding, namely -0.3 ± 0.5 versus 0.6 ± 0.5 mg leucine/kg/h (P < 0.001).
  
  
  CONCLUSIONS
  In the patient group studied, hypocaloric feeding was associated with a more negative protein balance, but the amino acid oxidation was not different. The protein kinetics measurements and the study's investigational protocol were useful for assessing the efficacy of nutrition support on protein metabolism in critically ill patients.
authors.forename: Agneta
authors.initials: A
authors.lastname: Berg
authors.forename: Olav
authors.initials: O
authors.lastname: Rooyackers
authors.forename: Bo-Michael
authors.initials: BM
authors.lastname: Bellander
authors.forename: Jan
authors.initials: J
authors.lastname: Wernerman
mesh_terms: D000328:Adult; D016638:Critical Illness / Q000628:therapy*; D002149:Energy Intake / Q000502:physiology*; D004734:Energy Metabolism / Q000502:physiology*; D005260:Female; D006801:Humans; D007700:Kinetics; D008297:Male; D008875:Middle Aged; D009752:Nutritional Status / Q000502:physiology; D010288:Parenteral Nutrition / Q000379:methods*; D010649:Phenylalanine / Q000008:administration & dosage / Q000097:blood*; D010865:Pilot Projects; D011506:Proteins / Q000008:administration & dosage / Q000378:metabolism; D012121:Respiration, Artificial / Q000379:methods
chemical_list: D011506:Proteins; D010649:Phenylalanine