Urea removal during continuous hemodiafiltration

Objective: To compare urea nitrogen removal by continuous hemodiafiltration vs. functional native kidneys in critically ill, septic patients receiving >2 g of amino acids/kg body weight per day. Design: Prospective, comparative, unblinded study. Setting: Trauma critical care units of a Level I adult trauma hospital. Patients: Fifteen septic patients with multiple organ failure including renal failure who were receiving continuous hemodiafiltration; 11 septic patients with multiple organ failure without renal failure (control group). Ages of patients ranged from 18 to 60 yrs. Interventions: Collection of effluent (dialysate + ultrafiltrate) from hemodiafilters. Collection of urine from control patients. Measurements: Urea nitrogen and creatinine concentrations in blood, urine, and the hemodiafiltration effluent, measured every 24 hrs for 6 days. Effluent and urine volumes were measured. Main Results: Hemodiafilters were operational for 21.8 ± 3.0 hrs/day. Mean urea nitrogen removal in the renal failure group was 28 ± 10 g/day. Blood urea nitrogen was stable over the 6-day study period. In control subjects, urea nitrogen removal was 27 ± 9 g/day, which was not significantly different from the continuous hemodiafiltration group. Blood urea nitrogen concentrations in control patients increased over the 6- day study period (p < .05). Urea nitrogen removal correlated moderately well with amino acid intake in the control group (r² = .30), but not in the continuous hemodiafiltration group (r² = .0004). In patients receiving continuous hemodiafiltration, effluent volume was most significantly correlated with urea nitrogen removal (r² = .69) Conclusions: The technique of continuous hemodiafiltration can remove substantial amounts of urea nitrogen, similar to that of normal native kidneys. In addition, at amino acid intake rates of >2 g/kg body weight/day, urea nitrogen removal during continuous hemodiafiltration remains a function of effluent volume, so there is no need to restrict amino acid intake in acute renal failure patients supported with continuous hemodiafiltration.