Continuous arteriovenous hemodialysis: Effect of dialyzer geometry

Abstract

Continuous arterio-venous hemodialysis (CAVHD) is an alternative to conventional hemodialysis for treating acute renal failure in critically ill patients [1, 2]. With this technique, a high flux dialyzer is connected to the arterial and venous blood circuit and dialysate is administered counter-current to the direction of blood flow [1, 2]. In this configuration, both diffusive clearance and ultrafiltration occur continuously but at relatively low blood and dialysate flow rates. Since CAVHD uses the patients' arterial blood pressure to circulate blood through the extracorporeal circuit, it is often better tolerated than standard hemodialysis in hemodynamically unstable patients [1]. Moreover, the large ultrafiltration capacity and diffusive clearances of CAVHD devices potentially permits control of fluid balance and biochemical manifestations of uremia [2]. A variety of high flux membranes of different composition are available in both parallel plate and hollow fiber configurations for use in CAVHD. Whereas the performance of parallel plates and hollow fiber dialyzers are roughly equivalent when used in high flow rate hemodialysis [3], dialyzer configuration may influence clearance during CAVHD. In particular, clearances could be limited in hollow fiber dialyzers, which have high flow resistance and consequently, a greater tendency for unstirred layers and/or flow mismatches between dialysate and blood at low flow rates [3]. Whether important differences exist between parallel plates and hollow fiber dialyzers with regard to performance in CAVHD is unknown. Thus, to evaluate the role of dialysis configuration in CAVHD, we performed a crossover study that sequentially used parallel plates and hollow fiber artificial kidneys in acute renal failure patients treated with CAVHD.