A positive fluid balance is associated with poor lung and
kidney function,1,2 delayed return of gastrointestinal function
after surgery3 and increased mortality.4 The association
of a positive fluid balance with adverse outcomes is
believed to be due to extracellular compartment expansion,
as water distributes to both intracellular and extracellular
spaces. However, sodium only distributes into the
extracellular space, which may have differential effects on
extracellular volumes, cause cellular dehydration and
exacerbate interstitial oedema in the systemic and pulmonary
circulations.