title: The consequences of sudden fluid shifts on body composition in critically ill patients.
abstract: BACKGROUND
  Estimation of body composition as fat-free mass (FFM) is subjected to many variations caused by injury and stress conditions in the intensive care unit (ICU). Body cell mass (BCM), the metabolically active part of FFM, is reported to be more specifically correlated to changes in nutritional status. Bedside estimation of BCM could help to provide more valuable markers of nutritional status and may promote understanding of metabolic consequences of energy deficit in the ICU patients. We aimed to quantify BCM, water compartments and FFM by methods usable at the bedside for evaluating the impact of sudden and massive fluid shifts on body composition in ICU patients.
  
  
  METHODS
  We conducted a prospective experimental study over an 6 month-period in a 18-bed ICU. Body composition of 31 consecutive hemodynamically stable patients requiring acute renal replacement therapy for fluid overload (ultrafiltration ≥5% body weight) was investigated before and after the hemodialysis session. Intra-(ICW) and extracellular (ECW) water volumes were calculated from the raw values of the low- and high-frequency resistances measured by multi-frequency bioelectrical impedance. BCM was assessed by a calculated method recently developed for ICU patients. FFM was derived from BCM and ECW.
  
  
  RESULTS
  Intradialytic weight loss was 3.8 ± 0.8 kg. Percentage changes of ECW (-7.99 ± 4.60%) and of ICW (-7.63 ± 5.11%) were similar, resulting ECW/ICW ratio constant (1.26 ± 0.20). The fall of FFM (-2.24 ± 1.56 kg, -4.43 ± 2.65%) was less pronounced than the decrease of ECW (P < 0.001) or ICW (P < 0.001). Intradialytic variation of BCM was clinically negligible (-0.38 ± 0.93 kg, -1.56 ± 3.94%) and was significantly less than FFM (P < 0.001).
  
  
  CONCLUSIONS
  BCM estimation is less driven by sudden massive fluid shifts than FMM. Assessment of BCM should be preferred to FFM when severe hydration disturbances are present in ICU patients.
authors.forename: Sophie
authors.initials: S
authors.lastname: Ismael
authors.forename: Magali
authors.initials: M
authors.lastname: Savalle
authors.forename: Claire
authors.initials: C
authors.lastname: Trivin
authors.forename: Florence
authors.initials: F
authors.lastname: Gillaizeau
authors.forename: Christian
authors.initials: C
authors.lastname: D'Auzac
authors.forename: Christophe
authors.initials: C
authors.lastname: Faisy
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001823:Body Composition / Q000502:physiology*; D016638:Critical Illness / Q000628:therapy*; D005260:Female; D018495:Fluid Shifts / Q000502:physiology*; D006801:Humans; D007362:Intensive Care Units / Q000639:trends*; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D006435:Renal Dialysis / Q000009:adverse effects / Q000639:trends*