Acute kidney injury (AKI) is an increasingly common and potentially catastrophic complication in critically ill patients. The incidence of AKI increases in recent years; about half of all patients in the intensive care units (ICU) develop AKI. AKI is associated with a significantly increased length of hospital stay and high mortality rates. Approximately, 50% of AKI is induced by sepsis.
Continuous renal replacement therapy (CRRT) has become routine for patients with AKI, chronic renal failure, fluid overload as well as oliguria in ICU. In clinical practice, continuous venovenous hemofiltration (CVVH) is actually the method of choice for CRRT in critically ill and hemodynamic instable patients. CVVH has significant beneficial effects on removing inflammatory cytokines, improving oxygen index, decreasing vasopressor requirements, increasing cardiac index, and regulating immune dysfunction, specifically in patients with septic shock. So far, there is no uniform standard to define the timing of discontinuation of CRRT for AKI, as predicting recovery of renal function in patients with AKI during CRRT is difficult. The Beginning and Ending Supportive Therapy for the Kidney (BEST Kidney) study suggested the urinary output > 500ml per day as the predictor for successful discontinuation of CRRT. However, the urinary output is often affected by clinical interventions (e.g. using diuretics). Thus, it is of great importance to find out a reliable biomarker to reflect the renal function of the patients who receiving CRRT. Cystatin (Cys) C has received the most interest in previous studies. The results showed serum Cys C concentrations were declined in different types of RRT (including intermittent hemodialysis and CVVH). This indicates Cys C is unfit as an indicator for persistent renal injury or renal recovery in critically ill patients during CRRT.
Neutrophil gelatinase-associated lipocalin (NGAL), a 25-kDa protein that covalently binds to gelatinase from neutrophils, is generally expressed at very low levels in several human tissues, however, in case of ischemia, infection, or toxic damage, NGAL rapidly released by activated neutrophils. Numerous studies have confirmed NGAL as a better indicator of AKI than serum creatinine (SCr). Schilder and colleagues reported that the plasma level of NGAL in critically ill patients with AKI is not affected by continuous venovenous hemofiltration (CVVH). However, it remains unclear if this also applies to sepsis-induced AKI, as considerable evidence suggests that the pathophysiology of septic AKI is different from other causes of AKI.
