The role of a "volume sparing" strategy in kidney replacement therapy of AKI: a retrospective single-center study.

Background: The KDIGO recommendation in acute kidney injury (AKI) patients requiring kidney replacement therapy is to deliver a Urea Kt/V of 1.3 for intermittent thrice weekly hemodialysis, and an effluent volume of 20-25 ml/kg/hour when using continuous renal replacement therapy (CRRT). Considering that prior studies have suggested equivalent outcomes when using CRRT-prolonged intermittent renal replacement therapy (PIRRT) effluent doses below 20 mL/kg/h, our group investigated the possible benefits of low effluent volume CRRT-PIRRT (12.5 ml/Kg/hour).

Methods: Thirty-six AKI patients that had been treated in the previous 12 months by CRRT-PIRRT with low effluent volume were included in the present retrospective observational study. The total effluent volume, derived from the formula [25 (or 12.5 ml) × kg body weight × 24], was administered over 24 h in CRRT and over 10 h in daily PIRRT. The control group consisted of the last 36 AKI patients previously treated with standard effluent volume CRRT (25 ml/kg/hour). Mortality within 90 days, shift from low effluent volume to standard effluent volume due to dialysis inadequacy, and remission of AKI were the end points. The two groups were homogeneous for age, sex, and sequential organ failure assessment (SOFA) score. Patients with AKI caused by metformin-induced lactic acidosis were excluded because they were treated with standard effluent volume CRRT until the lactic acidosis was corrected by subsequently reducing the effluent volume to 12.5 ml/kg/hour.

Results: The two groups were homogeneous as for baseline features. The UKt/V in the low effluent volume group was 0.51 ± 0.04 in CRRT and 0.50 ± 0.07 in PIRRT per session (Table 3). The UKt/V in the standard effluent volume group was 1.00 ± 0.02 in CRRT and 0.95 ± 0.05 in PIRRT per session. No differences were observed between the 2 groups regarding death from any cause at 90 days, and recovery of renal function. No patient was switched from low effluent volume to standard effluent volume due to inadequate control of uremic toxins. Serum creatinine at discharge from the hospital in patients with no KRT dependence was 2.1 ± 0.6 mg/dl in standard effluent volume and 1.9 ± 0.5 in low effluent volume (p = 0.37). All low effluent volume patients showed adequate metabolic, electrolyte, and acid-base profile control. In the low effluent volume group, the incidence of hypophosphatemia was lower than in the standard effluent volume group (5 vs 15, p = 0.003).

Conclusions: In this single-center retrospective study, low effluent volume CRRT-PIRRT was associated with similar outcomes to standard effluent volume CRRT-PIRRT, which is consistent with the results of prior observational studies. Randomized controlled studies comparing low effluent volume with standard effluent volume are needed.