Fluid overload in AKI: epiphenomenon or putative effect on mortality?

PURPOSE OF REVIEW: The incidence of acute kidney injury (AKI) is increasing dramatically, and despite advances in dialytic therapy and critical care, there has been little improvement in associated morbidity and mortality. Recently, several articles have suggested that fluid overload in patients with AKI is associated with an increased risk of death. RECENT
FINDINGS: Observational studies have demonstrated an association between fluid overload and poor outcomes (including death) in patients with AKI; however, whether this association is causal or due to residual confounding is unknown. A recent study testing the impact of fluid overload and diuretics on outcomes in the context of a randomized controlled trial suggests that the beneficial impact of diuretics in those with AKI is mediated by reducing fluid overload. Finally, potential mechanisms by which fluid overload may contribute to death include failure to recognize AKI due to creatinine dilution, direct tissue edema leading to decreased renal perfusion, and an increased risk of other complications such as sepsis.
SUMMARY: On the basis of the current literature, the relative contributions of the direct effects of fluid overload versus the association of fluid overload with other patient characteristics associated with adverse outcome (e.g. sepsis) remain unknown. Additional human studies, including randomized controlled trials, are warranted to further clarify these issues.