UREA REMOVAL DURING CONTINUOUS HEMODIAFILTRATION

Objective: To compare urea nitrogen removal by continuous hemodiafiltr ation vs. functional native kidneys in critically ill, septic patients receiving >2 g of amino acids/kg body weight per day. Design: Prospec tive, comparative, unblinded study. Setting: Trauma critical care unit s of a Level I adult trauma hospital. Patients: Fifteen septic patient s with multiple organ failure including renal failure who were receivi ng continuous hemodiafiltration; 11 septic patients with multiple orga n failure without renal failure (control group). Ages of patients rang ed from 18 to 60 yrs. Interventions: Collection of effluent (dialysate + ultrafiltrate) from hemodiafilters. Collection of urine from contro l 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 Result s: Hemodiafilters were operational for 21.8+/-3.0 hrs/day. Mean urea n itrogen removal in the renal failure group was 28+/-10 g/day. Blood ur ea nitrogen was stable over the 6-day study period. In control subject s, urea nitrogen removal was 27+/-9 g/day, which was not significantly different from the continuous hemodiafiltration group. Blood urea nit rogen concentrations in control patients increased over the 6-day stud y period (p<.05). Urea nitrogen removal correlated moderately well wit h amino acid intake in the control group (r(2)=.30), but not in the co ntinuous hemodiafiltration group (r(2)= .0004). In patients receiving continuous hemodiafiltration, effluent volume was most significantly c orrelated with urea nitrogen removal (r(2)=.69). Conclusions: The tech nique of continuous hemodiafiltration can remove substantial amounts o f 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 eff luent volume, so there is no need to restrict amino acid intake in acu te renal failure patients supported with continuous hemodiafiltration.