DO INDUCED SECONDARY FLOWS AUGMENT THE CLEARANCE OF PROTEIN-BOUND SUBSTANCES DURING ALBUMIN HEMODIAFIL-TRATION?

Abstract

Objective: Removal of protein-bound toxins such as bilirubin by albumin hemodiafiltration (HDF) has been applied in patients with hepatic failure. As toxins must he transferred from perfusate to dialysate albumin binding sites, the efficiency of HDF may be limited by the laminar flow in the filter compartments where only a thin layer of fluid contacts the fiber surface. We hypothesized that disruption of laminar flow through filter agitation would enhance bilirubin transfer during HDF. Methods: An in vitro continuous HDF circuit was used with fixed volume perfusate and dialysate compartments. Unconjugated bilirubin was added to sheep plasma (10 mg/dl) and perfused through an albumin-impregnated polyalkyl sulfone hemofilter against a recirculating albumin-rich dialysate (10 g/dl) with matched flow rates. One group of filters (n = 3) was vigorously agitated during HDF along its long axis at approximately 8 Hz. A second group (n = 3) remained stationary. Plasma bilirubin levels were maintained between 8 and 12 mg/dl by continuous infusion of bilirubin. Dialysate bilirubin concentrations were measured over 3 hours. Bilirubin transfer rates were compared using repeated-measures ANOVA. Results: At 3 hours, 19% more bilirubin was transferred by the agitated filter than by the stationary filter (22.5±3.8 vs. 18.9±2.3 mg, p = NS). The transfer rate was highest for both groups in the first 30 minutes, but was 70% greater in the agitated filter (0.233±0.064 vs. 0.137±0.024 mg/min, p=0.068). However, this rate difference was not maintained beyond 90 minutes. Conclusions: Bilirubin transfer may be enhanced by the introduction of secondary flows, especially in the first 90 minutes of HDF. Mixing at the fluid-fiber interface may be an important determinant of hemofilter performance. Further studies to elucidate the factors responsible may influence future hemofilter design and ultimately the efficiency of extra-corporeal hepatic support.