Biocompatibility issues in hemodialysis

Hemodialysis, as a life-saving treatment modality for uremic patients, implies a repeated and compulsory contact of blood with foreign materials. As a consequence, biocompatibility problems are unavoidable. The same applies for the material used for the creation of vascular access, and for the alternative dialysis method, CAPD (continuous ambulatory peritoneal dialysis), although each system might cause its own and specific problems. Although in early dialysis the focus has been on maintenance of life and elimination of toxins, later on the important morbid implications of this lack of biocompatibility have been recognized. Eight major problems will be discussed, especially in the perspective of recent new findings in this field: (1) coagulation and clotting; (2) complement and leukocyte activation; (3) susceptibility to infection; (4) leaching or spallation; (5) surface alterations of solid materials; (6) allergic reactions; (7) shear; (8) transfer of compounds from contaminated dialysate. After description of the major biochemical and clinical implications of these problems, ways to prevent morbid events and future perspectives will be described.

The effect of dialyzer reuse on peak expiratory flow rate

Peak expiratory flow rates were measured during routine haemodialysis in 18 patients with chronic renal failure who were in receipt of thrice weekly haemodialysis treatment, using both a new cuprophan dialyzer and then the same dialyzer after reprocessing. Acetate buffered dialysate was used on both occasions. The peak expiratory flow rates fell by 10 +/- 0.3%, mean +/- sem, during the first hour of treatment with the new dialyzer, and in seven patients (39%) the fall was greater than 15%. Whereas the reduction in peak expiratory flow rates was significantly less with reuse, 4 +/- 0.1% (P less than 0.5). Similarly, the fall in arterial oxygen tension was also reduced on reuse from 28 +/- 1.2% to 14 +/- 1.3% at 30 min (P less than 0.05) and from 30 +/- 1.4% to 18 +/- 3.1% (P less than 0.05) at 60 min of dialysis. There was also a reduction in the fall in the peripheral platelet count at 30 min of dialysis from 14 +/- 0.8% to 9 +/- 0.4% with reuse (P less than 0.05). However, there was no change in dialysis associated leukopenia with reuse of the dialyzer membrane. These results suggest that reprocessing the dialyzer membrane alters its biocompatibility characteristics resulting in an improvement in biocompatibility and further supports the role of inflammatory cell mediator release in the pathogenesis of dialysis associated hypoxaemia and pulmonary dysfunction during the first hour of dialysis treatment.

Development of anti-N-like antibodies during formaldehyde reuse in spite of adequate predialysis rinsing

The development of anti-N-like antibodies has been demonstrated with formaldehyde reuse of hemodialyzers. It has been recommended to pursue a postrinsing venous effluent formaldehyde concentration in the range of or below 2 to 10 ppm, in order to prevent the development of these anti-N-like antibodies. In the present study, we evaluated formaldehyde reuse in a population of 50 patients and whether the strict control of predialysis effluent formaldehyde concentration below 2 to 3 ppm could prevent the development of anti-N-like antibodies. Five of 50 patients (10%) became positive 6 to 14 months after the start of formaldehyde reuse, indicating that even a careful control of effluent formaldehyde concentration cannot prevent the occurrence of this abnormality.

Adequacy studies of fistula single-needle dialysis

The preferred method of vascular access for routine hemodialysis is via an arteriovenous fistula into which two needles are inserted. Single-needle access is an alternative to this method. Thorough evaluations of the efficiency of the single-needle method are lacking. The present study evaluates the weekly time-averaged urea concentrations (TACUrea) and protein intake (PI) in 76 patients routinely treated with single-needle dialysis on a chronic basis. Furthermore, other clinical parameters of dialysis adequacy, such as hematocrit, nerve conduction velocity, hospitalization rate, and cumulative survival also were evaluated, as well as fistula survival. TACUrea appeared to be 53.2 +/- 6.0 mg/100 mL, a value corresponding to adequate two-needle dialysis with low morbidity, as outlined by the American National Cooperative Study Group. PI was evaluated from urea generation rates (G) and from outpatient dietary records. G was 6.07 +/- 2.42 mg/min, and the corresponding PI was calculated to be 1.07 +/- 0.28 g/kg body weight/24 h. PI estimated from dietary records was 1.14 +/- 0.43 g/kg body weight/24 h. The relation of total clearance over distribution volume (KT/V) averaged 0.98 +/- 0.23. Mean hematocrit and nerve conduction velocity during 2 years of follow-up ranged between 24% and 26% and 38 and 40 m/s, respectively. Hospitalization rate during 1 year was 18%. Five years' cumulative survival was 64% for the period 1975 to 1985, and 79% for the period 1980 to 1985. Five years' fistula survival was 74%, a value higher than in four studies on two-needle dialysis of comparable extent. It is concluded that urea kinetic data and other parameters of dialysis adequacy indicate that the efficiency of the single-needle technique is at least as good as that obtained in the more currently used two-needle technique. Subsequently, the current reluctance towards single-needle dialysis as a routine procedure in chronic renal failure, appears to be unjustified.

Cuprophan reuse and intradialytic changes of lung diffusion capacity and blood gases

The changes in arterial blood gas, pulmonary function tests, leukocyte counts and complement activation were evaluated during first use and subsequent reuse of cuprophan dialyzers. The dialysate buffer was bicarbonate. Reuse of cuprophan dialyzers significantly attenuated the fall in leukocyte counts and the rise in C3a des Arg seen during first use dialysis. First use dialysis also caused a drop in arterial paO2 from 93.0 +/- 12.4 mm Hg to a nadir of 82.8 +/- 12.6 mm Hg at 60 minutes (P less than 0.01). PaO2 levels did not change when reused dialyzers were employed (93.7 +/- 12.2 before dialysis and 96.4 +/- 15.2 mm Hg at 60 minutes, P greater than 0.05). Intradialytic paO2 curves obtained during first use and reuse were significantly different by variance analysis (P less than 0.001). There was also a significant decline in lung diffusion capacity (DLCO, from 30.70 +/- 8.89 to 23.77 +/- 7.76 ml/min X mm Hg, P less than 0.01) and transfer factor (KCO, from 6.07 +/- 1.97 to 5.65 +/- 2.13 ml/min X mm Hg, P less than 0.01), during first use at one hour after initiation of dialysis. This decrease was entirely prevented during reuse, (P less than 0.001 vs. first use by variance analysis). Percentual changes in leukocyte counts and C3a des Arg concentration on one hand, and in paO2, DLCO and KCO on the other were significantly correlated to each other. Other factors with a possible influence on intradialytic pulmonary function such as ultrafiltration volume, dialysate buffer composition, evolution of intradialytic blood pH and cardiac output, were all identical under both experimental conditions.(ABSTRACT TRUNCATED AT 250 WORDS)