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Acute renal failure is another common type of organ failure associated with severe AP. Factors related to the development of acute kidney injury (AKI) are male sex, sepsis and septic shock, respiratory failure, age, development of abdominal compartment syndrome, and comorbidities according to a propensity score‐matched analysis [34]. In a study trying to develop a prediction rule for mortality in patients with AP in ICU and at least one organ failure [35], the presence of renal failure was not an independent predictor of mortality, but the need for continuous renal replacement therapy (CRRT) was an important mortality predictor.

The mechanisms of acute renal failure in AP patients are not well studied and the resulting kidney injury is likely multifactorial. Proposed mechanisms include hypovolemia (pre‐renal component, see preceding sections), hypoxemia‐driven injury to the renal tubular epithelial cells, impairment of renal microcirculation due to released pancreatic amylase, release of apoptotic molecules including cytokines from the inflamed pancreas leading to renal cellular injury, and abdominal compartment syndrome that may develop in patients with severe AP and lead to decreased renal perfusion pressure causing ischemic injury [36].

If a patient with AP develops renal failure, a global evaluation should be performed and volume infusion should be started in order to correct the hypovolemic state and the pre‐renal etiology of kidney injury. IAP should be continuously monitored in patients with AP and renal failure. It is worth bearing in mind that an increase in serum chloride and chloride exposure could also be associated with AKI [37], and thus the composition of replacement fluid, in addition to the volume infused, could be important. Normal saline is associated with a higher chloride concentration than balanced solutions such as lactated Ringer’s solution [29].

When renal failure is more severe, depuration techniques are needed. Conventional dialysis uses diffusion as the depuration mechanism and is performed over a short time period (3–4 hours), so it could be deleterious in hemodynamically unstable patients. CRRT offer two advantages in comparison to conventional dialysis: (i) the option for continuous management over 24 hours, with better hemodynamic tolerance; and (ii) the use of dispersion, convection and adsorption mechanisms to remove endotoxin and inflammatory mediators, to correct disorders in acid–base balance, adjust immune stability, and maintain stability of the internal environment. CRRT promotes good hemodynamic stability for patients with excessive load and high catabolism, which improves prognosis [38].

The optimal timing for initiation of CRRT in patients admitted to the ICU with AKI remains uncertain. Conventionally accepted indications include volume overload, hyperkalemia, metabolic acidosis, overt uremia, and even progressive azotemia in the absence of specific symptoms; however, precise definitions for these indications are lacking [39]. The optimal timing of initiation of renal replacement therapy for non‐life‐threatening indications of AKI also remains to be determined. There is a debate as to whether different strategies for initiation of renal replacement therapy (early vs. delayed) confer a survival benefit [40].

The concept of immunomodulation in AP, using CRRT, is very exciting, but results are not clear. Pulses of high‐volume hemofiltration can reduce levels of tumor necrosis factor (TNF)‐α, interleukin (IL)‐4, IL‐6, IL‐8 and IL‐10, but there are no data about the clinical impact on mortality or other relevant outcomes [41,42].

A recent meta‐analysis [43] of patients with AP and continuous blood purification showed that, compared with conventional treatment, continuous blood purification could reduce the incidence of organ failure, length of stay in the ICU, and mortality, but articles included in this study are of low quality and relevant multicenter randomized controlled trials are required to prove these findings.