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Although continuous renal replacement therapy (CRRT) is widely used for the treatment of acute kidney injury in intensive care units, controversy in the clinical application of this therapy continues. Results of two recently published randomized controlled trials—the ATN study and the RENAL trial—have now provided an unparalleled quantity of information to guide clinicians. Here, Prowle and Bellomo discuss the results of these trials, explain the controversies that still exist regarding the use of CRRT, and describe the questions that remain to be answered.

2012 saw the publication of four important trials investigating the choice of fluid therapy in patients suffering from critical illness or undergoing major surgery. These studies pave the way for more evidence-based administration of fluid in such patients.

The past decade has seen developments in several aspects of acute kidney injury (AKI), including the discovery of an array of biomarkers, assessment of the optimal dose intensity for renal replacement therapy, and the impact of fluid administration. Furthermore, AKI has emerged as an important risk factor for chronic kidney disease.

The consequences of fluid administration and the maintenance of fluid balance, despite their ubiquity in critical care, remain a topic of much debate among clinicians. Emerging evidence suggests that fluid administration and a positive fluid balance can be harmful in a number of conditions, including acute kidney injury.

Fluid therapy is essential to maintain renal oxygen delivery and glomerular filtration in patients who are at risk of acute kidney injury (AKI). However, patients with AKI are also at risk of fluid overload. This Review discusses the optimal fluid management strategy for patients with AKI, and the need to balance adequate shock resuscitation with the harmful effects of fluid overload.

Intravenous fluids are widely administered to patients who have, or are at risk of, acute kidney injury (AKI), but deleterious consequences of overzealous fluid therapy are increasingly being recognized. This Review describes the problems of fluid management in acquired AKI, and discusses the need to balance the competing needs of adequate fluid resuscitation, the avoidance of progressively positive fluid balances (which can lead to extracellular volume expansion and organ edema), and the possibility of overzealous fluid removal (which can lead to hypovolemic AKI).

Two recent randomized trials provide evidence to guide the management of sepsis. The CLASSIC trial reports that restrictive fluid therapy has no mortality benefit compared to a standard regimen in patients with septic shock, whereas the LOVIT trial reports that high-dose intravenous vitamin C might be harmful in patients with severe sepsis.

Cardiac surgery-associated acute kidney injury (CSA-AKI) is the most common complication in adult patients undergoing open heart surgery. In this Review, the authors discuss the definition, epidemiology, pathophysiology and risk factors of CSA-AKI. The authors also explore the use of novel biomarkers of AKI and their potential utility in preventing or treating CSA-AKI.

Acute kidney injury (AKI) and chronic kidney disease are increasingly recognized as interconnected entities and the term acute kidney disease (AKD) has been proposed to define ongoing pathophysiologic processes following an episode of AKI. In this Consensus statement, the Acute Disease Quality Initiative 16 Workgroup propose definitions and staging criteria for AKD, and strategies for the management of affected patients. They also make recommendations for areas of future research with the aims of improving understanding of the underlying processes and improving outcomes.

Several factors complicate the identification of effective interventions that can improve the outcomes of patients with acute kidney injury (AKI). Here, the authors discuss key design considerations for clinical trials in hospitalized patients with AKI, including the selection of adequate patient cohorts and study end points.

The concepts of kidney damage and dysfunction, including subclinical damage and loss of renal functional reserve, are relevant to the detection of acute kidney injury (AKI). Here, the authors examine these concepts, as well as AKI duration and relapse, and discuss potential changes to AKI classification criteria.

Sepsis-associated acute kidney injury (SA-AKI) is linked with poor outcomes in critically ill patients. This Consensus Statement from the Acute Disease Quality Initiative discusses the definition, epidemiology and pathophysiology of SA-AKI, fluid, resuscitation and extracorporeal therapies, and the role of biomarkers in risk stratification and diagnosis.

Here, the authors describe the mechanisms of ultrafiltration during kidney replacement therapy, the effects of ultrafiltration on cardiovascular physiology and the principles of volume management in critically ill patients. They also discuss potential mechanisms that could underlie the association between ultrafiltration rate and organ dysfunction.

This Review updates the evidence base for the administration of intravenous fluids to critically ill patients. Finfer and colleagues also discuss unresolved questions, such as whether buffered solutions are better than normal saline, and the benefits and harms of restrictive approaches to fluid administration.

Pickering et al. report that unchanging plasma creatinine levels after resuscitated cardiac arrest can indicate substantial acute kidney injury (AKI) as confirmed by increased levels of AKI biomarkers and increased mortality. This finding illustrates the limitations of plasma-creatinine-based diagnosis of AKI in early critical illness.