Continuous arteriovenous hemodiafiltration

Abstract

As demonstrated by the above examples, in CAVHD blood access is usually obtained through femotal catheters, the blood flow rate is not routinely measured and the dialysate flow rate is arbitratily set to 1 to 2 L/hr. In this way, the treatment proved genetally effective. However, sometimes problems were encountered. In some patients frequent clotting of dialyzers occurred, probably because blood flow rate was too low. Sometimes plasma urea levels did not come down as quickly as we had expected or levels of phosphate were found to become too low. There was vinually no insight in the determinants of transpon rates and the dialysate flow rate that is necessary. It was not known to what extent CAVHD treatment had influence on the disappearance rate of drugs. Therefore, in 1989 a study was begun of the detenninams of blood flow rate, ultrafiltration and solute transpon rate in CAVHD, so as to be able to optimize CAVHD treatmentThe aims of this srudy can be sUllllilalized as follows: 1. Analysis of the determinants of blood flow rate. The resistance to flow rate of catheters and dialyzers was studied and the influence of blood viscosity was analyzed. A method was investigated for the determination of blood flow rate by using a probe outside the blood line. 2. Analysis of the determinants of ultrafiltration and convective rranspon rate. The transmembrane pressure difference and the hydraulic permeability of dialyzers were determined as well as the change in hydraulic permeability over time. Funhermore, the 'sieving coefficients' were determined for a number of clinically relevant solutes. 3. Analysis of the determinants of the diffusive transpon rate. A mathematical model of combined convection and diffusion was developed and used to determine the diffusive mass transfer coefficiem of a number