title: Sodium balance, not fluid balance, is associated with respiratory dysfunction in mechanically ventilated patients: a prospective, multicentre study.
abstract: BACKGROUND
  Large positive sodium balances, independent of fluid balance, may lead to expanded extracellular fluid volumes and adverse clinical outcomes in the critically ill, including impaired oxygenation.
  
  
  OBJECTIVE
  To estimate sodium and fluid balances in critically ill patients needing invasive mechanical ventilation (MV) for more than 48 hours and to evaluate the relationship between fluid balance, sodium balance and respiratory function (PaO2/FiO2 ratio and length of MV).
  
  
  METHODS
  A prospective, observational study of 50 patients on MV in four tertiary intensive care units.
  
  
  METHODS
  Daily sodium and fluid input and output, biochemistry, haemodynamic variables, oxygenation (PaO2/FiO2) and steroid and vasopressor administration were recorded for 3 days after study enrolment. Outcome data included the duration of invasive MV, ICU and hospital mortality and ICU and hospital lengths of stay.
  
  
  RESULTS
  Fifty patients (33 men [66%]) with a mean age of 62.8 years (standard deviation, 14.6 years) and a median admission Acute Physiology and Chronic Health Evaluation III score of 82 (interquartile range [IQR], 61-99) were studied. By Day 3 after enrolment, the median cumulative fluid balance was 2668 mL (IQR, 875-3507 mL) and the cumulative sodium balance was +717 mmol (IQR, +422 to +958 mmol). Intravenous steroids and the presence of shock led to a lower daily sodium excretion (P=0.004 and P=0.01, respectively). A positive sodium balance was associated with a reduction in the next day's PaO2/FiO2 ratio (ρ=-0.36, P=0.001) and an increased length of MV (linear regression analysis, P<0.01). The cumulative fluid balance was not associated with either parameter.
  
  
  CONCLUSIONS
  The cumulative positive sodium balance, not the cumulative positive fluid balance, is associated with respiratory dysfunction and an increased length of MV.
authors.affiliation: Department of Critical Care Medicine, Flinders University, Adelaide, SA, Australia. biharishailesh@gmail.com.
authors.forename: Shailesh
authors.initials: S
authors.lastname: Bihari
authors.affiliation: School of Medicine, University of Adelaide, Adelaide, SA, Australia.
authors.forename: Sandra L
authors.initials: SL
authors.lastname: Peake
authors.affiliation: Department of Critical Care Medicine, Flinders Medical Centre, Adelaide, SA, Australia.
authors.forename: Shivesh
authors.initials: S
authors.lastname: Prakash
authors.affiliation: Critical Care and Trauma Division, The George Institute for Global Health, Sydney, NSW, Australia.
authors.forename: Manoj
authors.initials: M
authors.lastname: Saxena
authors.affiliation: Intensive Care Unit, Nambour General Hospital, Nambour, QLD, Australia.
authors.forename: Victoria
authors.initials: V
authors.lastname: Campbell
authors.affiliation: Department of Critical Care Medicine, Flinders University, Adelaide, SA, Australia.
authors.forename: Andrew
authors.initials: A
authors.lastname: Bersten
mesh_terms: D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012121:Respiration, Artificial / Q000009:adverse effects*; D012131:Respiratory Insufficiency / Q000209:etiology*; D012964:Sodium / Q000378:metabolism*; D014882:Water-Electrolyte Balance / Q000502:physiology*
chemical_list: D012964:Sodium