Sepsis-associated acute kidney injury (SA-AKI) is common in critically ill patients and is strongly associated with adverse outcomes, including an increased risk of chronic kidney disease, cardiovascular events and death. The pathophysiology of SA-AKI remains elusive, although microcirculatory dysfunction, cellular metabolic reprogramming and dysregulated inflammatory responses have been implicated in preclinical studies. SA-AKI is best defined as the occurrence of AKI within 7 days of sepsis onset (diagnosed according to Kidney Disease Improving Global Outcome criteria and Sepsis 3 criteria, respectively). Improving outcomes in SA-AKI is challenging, as patients can present with either clinical or subclinical AKI. Early identification of patients at risk of AKI, or at risk of progressing to severe and/or persistent AKI, is crucial to the timely initiation of adequate supportive measures, including limiting further insults to the kidney. Accordingly, the discovery of biomarkers associated with AKI that can aid in early diagnosis is an area of intensive investigation. Additionally, high-quality evidence on best-practice care of patients with AKI, sepsis and SA-AKI has continued to accrue. Although specific therapeutic options are limited, several clinical trials have evaluated the use of care bundles and extracorporeal techniques as potential therapeutic approaches.
Definition and epidemiology of SA-AKI
Definition of SA-AKI and sepsis-induced AKICurrently, no universally accepted definition of SA-AKI exists 15 . To support clinical guidelines, quality improvement initiatives, and future research, we propose that the presence of both sepsis (as currently defined in adults by the Sepsis-3 criteria) and AKI (as presently defined by the Kidney Disease: Improving Global Outcomes (KDIGO) criteria) should define SA-AKI 1,16 (Box 1). SA-AKI is a heterogeneous syndrome that occurs as the consequence of either direct mechanisms related to infection or the host response to infection, or indirect mechanisms driven by unwanted sequelae of sepsis or sepsis therapies 17 . As such, the term SA-AKI operationally unifies the presence of AKI (according to clinical, biochemical and functional criteria) in the context of sepsis as a specific disease phenotype that is characterized by a specific trajectory and outcome 18,19 .Sepsis-induced AKI (SI-AKI) can be considered to be a subphenotype of SA-AKI, in which sepsis-induced mechanisms drive kidney damage directly. Thus, by definition, SI-AKI excludes injury that primarily develops as the indirect consequence of sepsis or sepsis therapies (for example, AKI caused by antimicrobial agent-induced nephrotoxicity or abdominal compartment syndrome) 20,21 . Importantly, mechanisms that underlie cellular and organ injury in ischaemic AKI or nephrotoxic AKI, such as microcirculation failure, inflammation and mitochondrial injury, might also contribute to SI-AKI. The limited availability of clinical tools such as biomarkers that can aid early identification complicate Many aspects of SA-AKI rema...