Fluid composition and acute kidney injury

Purpose of review To describe recent advances in the understanding of the role of fluid composition in renal outcomes in critically ill patients. Recent findings The debate on fluid composition is now focused in a pragmatic discussion on fluid electrolyte composition. The resurgence of this debate was propelled by several observational studies that suggested that balanced (i.e., low chloride) solutions were associated with less acute kidney injury in critically ill patients. Nevertheless, a cluster randomized trial failed to show any benefit of balanced solutions. This trial, however, may have failed to detect an effect because of low global illness severity and little fluid infused. If balanced solutions are to be associated with less acute kidney injury, it will probably be in high risk, aggressively resuscitated patients. Additionally, the causal loop involving unbalanced solution infusion, induction of hyperchloremia and acute kidney injury is yet to be closed. Other factors, such as buffer type, speed of infusion and temperature, among others, may also be important. Summary Recent evidence suggests that crystalloid fluid composition matters and can influence renal outcomes in critically ill patients. Further studies should assess the impact and cost-efficiency of balanced solutions in the context of high-risk scenarios.