Uremic Toxicity: Present State of the Art

The uremic syndrome is a complex mixture of organ dysfunctions, which is attributed to the retention of a myriad of compounds that under normal condition are excreted by the healthy kidneys (uremic toxins). In the area of identification and characterization of uremic toxins and in the knowledge of their pathophysiologic importance, major steps forward have been made during recent years. The present article is a review of several of these steps, especially in the area of information about the compounds that could play a role in the development of cardiovascular complications. It is written by those members of the Uremic Toxins Group, which has been created by the European Society for Artificial Organs (ESAO). Each of the 16 authors has written a state of the art in his/her major area of interest.

A time for rediscovery: chronic hemofiltration for end-stage renal disease

Provision of maintenance renal replacement therapy (MRRT) is becoming increasingly challenging. The number of patients requiring MRRT is growing rapidly, while the number of nephrologists, nurses, and other staff available to provide therapy is not increasing at a similar rate. Patients are now older and have more comorbid conditions, which magnifies the complexity of their RRT and makes it increasingly difficult to maintain the quality of care within the limitations of constrained economic resources. The two most commonly used MRRTs are hemodialysis (HD) and peritoneal dialysis (PD). A third modality of MRRT, hemofiltration, is not currently in widespread use in North America. In hemofiltration, plasma is filtered through a highly permeable, biocompatible synthetic membrane and waste products are removed by convection and solvent drag as the filtrate moves across the membrane. Hemofiltration equipment constantly monitors the rate of plasma removal and administers a sterile, nonpyrogenic replacement solution at an appropriate rate to replace the waste-laden ultrafiltrate and avoid vdume depletion in the patient. Hemofiltration may offer some potential clinical advantages to the MRRT patient, including better hemodynamic and cardiovascular stability, enhanced removal of middle molecular weight toxins, increased comfort, and therapy preference. Some reports indicate possible reduced morbidity and mortality and reduced risk of bacterial contamination and inflammation as a result of the use of sterile, ultrapure replacement fluids. Chronic hemofiltration is a relatively simple MRRT option that may offer significant benefits for many patients who have end-stage renal disease (ESRD) and deserves closer consideration for these patients.

Principles and practice of hemofiltration and hemodiafiltration

There is growing interest in the convective dialysis therapies, hemofiltration (HF) and hemodiafiltration (HDF). Both require dialysis membranes which are highly permeable to solutes as well as fluid, and in both cases large volumes of ultrafiltration are the condition for convective transport. In HDF the convection is combined with diffusion, and as a consequence, maximum clearance over the entire molecular weight spectrum is achieved. Optimal forms of HDF provide urea clearance 10-15% higher than the corresponding diffusive mode. The larger the solute, the greater is the impact of convection, and beta2-microglobulin (beta2m) levels may be up to 70% reduced. Traditional postdilution HF provides high clearance of medium sized and large molecules. Satisfactory clearance of small solutes requires blood flows in excess of 500 ml/min. With access to practically unlimited volumes of substitution solution through on-line ultrafiltration, predilution HF can now be used. This increases the clearance of small solutes to an acceptable range. For HDF as well as HF, large patient populations consistently treated for longer periods of time are needed to make valid outcome comparisons with other therapies.