title: Bioelectrical impedance vector analysis in critically ill patients: a prospective, clinician-blinded investigation.
abstract: BACKGROUND
  Assessment of fluid status in critically ill patients is challenging. We aimed to assess the feasibility and validity of bioelectrical impedance vector analysis (BIVA) as a measure of hydration in critically ill patients.
  
  
  METHODS
  We performed twice-daily BIVA measurements and fluid balance calculations and recorded physiological variables in mechanically ventilated patients within 24 h of intensive care unit (ICU) admission for up to 5 days. Treating clinicians were blinded to BIVA results.
  
  
  RESULTS
  We performed 344 BIVA measurements in 61 patients. According to BIVA, 14 patients (23%) were dehydrated, 22 (36%) were normally hydrated and 25 (41%) were overhydrated upon ICU admission. Patients with normal BIVA hydration were less sick, had fewer comorbidities and had less deranged physiology than patients found to be dehydrated or overhydrated with BIVA. Cumulative fluid balance increased in patients found to be dehydrated with BIVA by a mean of 3.4±2.2 L, whereas in patients found to be overhydrated with BIVA, it decreased by a mean of 4.5±6.9 L. In patients found to be normally hydrated with BIVA, fluid balance remained unchanged. BIVA-defined hydration increased with 1 L (median change 1.5%, P =0.09) or 2 L (median change 0.7%, P =0.09) of calculated fluid gains. BIVA-defined hydration decreased (median change -0.8%, P =0.02) with a negative cumulative fluid balance of >2 L. BIVA-defined hydration between first and last measurement correlated with the corresponding change in fluid balance (ρ =0.25, P =0.05).
  
  
  CONCLUSIONS
  BIVA is feasible in critically ill patients. Its validity is supported by the observed characteristics of patients with different degrees of BIVA hydration upon admission and by different fluid management of such patients by blinded clinicians. The sensitivity of repeated BIVA hydration measurements to detect fluid accumulation or fluid balance changes <2 L was low, however. These contradictory findings provide the rational basis for studies of BIVA-assisted fluid management in ICU patients.
authors.affiliation: Department of Intensive Care, Austin Hospital, Austin Health, Heidelberg, Melbourne, VIC, 3084, Australia. sarahjones21@doctors.org.uk.
authors.forename: Sarah L
authors.initials: SL
authors.lastname: Jones
authors.affiliation: Department of Intensive Care, Austin Hospital, Austin Health, Heidelberg, Melbourne, VIC, 3084, Australia. aiko.tanaka@austin.org.au.
authors.forename: Aiko
authors.initials: A
authors.lastname: Tanaka
authors.affiliation: Department of Intensive Care, Austin Hospital, Austin Health, Heidelberg, Melbourne, VIC, 3084, Australia. glenn.eastwood@austin.org.au.|Australian and New Zealand Intensive Care Research Centre, School of Preventive Medicine and Public Health, Monash University, Melbourne, VIC, Australia. glenn.eastwood@austin.org.au.
authors.forename: Glenn M
authors.initials: GM
authors.lastname: Eastwood
authors.affiliation: Department of Intensive Care, Austin Hospital, Austin Health, Heidelberg, Melbourne, VIC, 3084, Australia. helen.young@austin.org.au.
authors.forename: Helen
authors.initials: H
authors.lastname: Young
authors.affiliation: Department of Intensive Care, Austin Hospital, Austin Health, Heidelberg, Melbourne, VIC, 3084, Australia. leah.peck@austin.org.au.
authors.forename: Leah
authors.initials: L
authors.lastname: Peck
authors.affiliation: Department of Intensive Care, Austin Hospital, Austin Health, Heidelberg, Melbourne, VIC, 3084, Australia. rinaldo.bellomo@austin.org.au.|Australian and New Zealand Intensive Care Research Centre, School of Preventive Medicine and Public Health, Monash University, Melbourne, VIC, Australia. rinaldo.bellomo@austin.org.au.
authors.forename: Rinaldo
authors.initials: R
authors.lastname: Bellomo
authors.affiliation: Department of Intensive Care, Austin Hospital, Austin Health, Heidelberg, Melbourne, VIC, 3084, Australia. johan.martensson@austin.org.au.|Section of Anaesthesia and Intensive Care Medicine, Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden. johan.martensson@austin.org.au.
authors.forename: Johan
authors.initials: J
authors.lastname: Mårtensson
mesh_terms: D000328:Adult; D000368:Aged; D016638:Critical Illness; D003681:Dehydration / Q000175:diagnosis*; D017097:Electric Impedance; D005240:Feasibility Studies; D005260:Female; D005440:Fluid Therapy; D006801:Humans; D007362:Intensive Care Units; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012121:Respiration, Artificial; D016037:Single-Blind Method; D014882:Water-Electrolyte Balance