Acute kidney injury (AKI) is a very common and especially formidable clinical problem in the ICU, where mortality rates approach 25% and soar to 50 to 60% when severe enough to require renal replacement therapy [1]. These statistics have not significantly improved over the past 50 years, though patients today are generally older and have more comorbidities [1]. The most common cause of AKI in hospitalized patients is sepsis [2], and AKI occurs with regularity even in non-severe sepsis where clinically evident hemodynamic changes are not readily apparent [3]. The combination of sepsis and AKI portends a dire clinical situation that is associated with a hospital mortality rate as high as 70% [4]. However, the basic pathophysiologic mechanisms undergirding the association between sepsis and the clinical manifestations of AKI are not completely understood.
In this review, we will first summarize the findings of published human studies that support the concept that the pathogenesis of septic AKI in humans should not be exclusively viewed in the context of distributive shock-associated ischemia, but rather also within the context of a dysregulated and ill-defined inflammatory response to septic stimuli. We then discuss why previous attempts at modulating the inflammatory response in septic AKI may have failed, and highlight more recent trials and therapies aimed at targeted treatment based on where patients lie along the immunologic spectrum. We also discuss the role Toll-like receptors (TLRs) have been shown to play in endotoxemic models of AKI, and again focus on why agents used to block TLR-related pathways may have failed to show significant clinical benefit. Finally, we review the data supporting and refuting a central role for apoptosis in septic AKI, and argue that much of the clinical manifestations in septic AKI occur prior to significant cell death secondary to apoptosis or necrosis.