Acute kidney injury (AKI) is frequently a part of multiorgan dysfunction syndrome in critically ill patients in the intensive care unit (ICU), and a significant portion, about 2% in some reports,1 will require renal replacement therapy (RRT). There is controversy about the optimal treatment of AKI regarding modality, dose, and appropriate timing of RRT.
RRT for AKI can be classified as intermittent or continuous, based on the duration of treatment. The duration of intermittent therapy is less than 24 hours, whereas the duration of continuous therapy is at least 24 hours. Intermittent RRT (IRRT) includes intermittent hemodialysis (IHD) and sustained low-efficiency dialysis (SLED). SLED refers to hemodialysis performed with a conventional dialysis machine over a longer time period (usually ≥ 5 hours) than traditional IHD. Continuous therapies include peritoneal dialysis and continuous RRT (CRRT). The 4 main types of CRRT by mechanism of solute removal are slow continuous ultrafiltration (fluid removal only); continuous venovenous hemofiltration (CVVH) (convection); CVV hemodialysis (CVVHD) (diffusion); and CVV hemodiafiltration (CVVHDF) (concurrent diffusion with convection). In developed countries, peritoneal dialysis is rarely used for AKI in the ICU setting because it provides inefficient solute clearance, increases the risk of peritonitis, and compromises respiratory function. In developing countries, peritoneal dialysis is still used for AKI due to low maintenance and cost.
MODALITIES OF RRT: IRRT VERSUS CRRT
Whether IRRT or CRRT influences clinical outcomes remains the subject of debate. Even though the worldwide standard RRT in the ICU is IHD, survey evidence has consistently shown considerable variation in RRT practice patterns. In recent years, the use of SLED has risen and is mainly driven by its convenience and lower cost compared to CRRT.
Several nonrandomized studies have suggested that CRRT may contribute to improved survival and a higher rate of renal recovery; however, other similar studies have failed to show any additional benefit with CRRT. The first randomized controlled trial (RCT) was done in 2001 by Mehta et al.2 IHD was averaged 5 days/week for 3 to 4 hours per session. Univariate intention-to-treat analysis revealed a higher mortality among patients receiving CRRT. However, multivariate analysis revealed no impact of RRT modality on all-cause mortality or recovery of renal function. Because Mehta et al, there have been 8 RCTs, comparing CRRT and IRRT (Table 71–1) (IHD,3,4,5,6,7,8 SLED9,10). There is significant variation among these RCTs in terms of study population (exclusion of chronic kidney disease, illness severity, and etiology of AKI), methods of RRT (criteria for RRT, device/technique, doses, and membrane material). Serious concerns have been identified in some trials due to unbalanced baseline characteristics, inappropriate sample size, and significant crossover between dialytic modalities.11 Most studies3,4,5,7,8 used IHD 3 times per week; however, recently, Lins et al6 performed ...