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Model-based study of the effects of the hemodialysis technique on the compensatory response to hypovolemia. Background. Hemodialysis technique (dialysate composition, filter, convection/diffusion ratio, etc.) can have an impact on the patient's tendency to acute hypotension. We have examined the hypothesis that the dialysis technique affects the hypotension risk by altering the cardiovascular compensatory response to hemodialysis-induced hypovolemia. Methods. Twelve hypotension-prone subjects were studied during six sessions of conventional bicarbonate dialysis (BD) and six sessions of acetate-free biofiltration (AFB). Blood volume (BV) control system was used in AFB to provide a BV change equivalent to the BV change observed in BD. The efficacy of reflex compensatory mechanisms was assessed by a model-based computer analysis of the BD and AFB sessions. Results. BD sessions were complicated by hypotension more frequently than the AFB ones (34/66 BD vs. 18/66 AFB). Hypotension arose about 60 minutes earlier in BD (123 ± 41 minutes in BD vs. 183 ± 25 minutes in AFB, P < 0.01), and after a smaller BV reduction (hypotension BV 7.9%± 2.0% in BD vs. 10.9%± 2.6% in AFB, P < 0.05). Model-based computer analysis of the sessions without hypotension revealed differences in peripheral resistance adaptation (9%± 9% BD vs. 19%± 7% AFB, P < 0.05) as well as in the stroke volume reduction (19%± 8% BD vs. 10%± 8% AFB, P < 0.001). Model analysis of sessions with hypotension indicated that compensatory mechanisms were almost inoperative in BD, whereas a residual capacity to control peripheral resistance and cardiac contractility was present in AFB. Model simulations demonstrated that hypotension occurred later in AFB since the residual compensatory capacity in AFB was able to sustain the arterial pressure for larger BV reductions (8.3% BD vs. 11.2% AFB). Conclusion. The increased risk of acute hypotension in BD compared to AFB is caused by a therapy-induced inhibition of reflex compensatory response to hypovolemia. [ABSTRACT FROM AUTHOR]

Background: Beta(2)-microglobulin (beta2-m) removal in patients with end-stage renal disease (ESRD) is maximal with convective techniques, such as hemofiltration (HF) or hemodiafiltration (HDF). Although the infusion mode of the replacement solution (predilution or postdilution) is expected to influence the efficiency of HF, experimental data in this respect are scanty. We therefore investigated the impact of the fluid reinfusion mode on the efficiency of HF in 11 ESRD patients who underwent both treatments., Methods: The dialyzer (AK 200 ULTRA) was equipped with a 3-layer polyamide membrane (Poliflux 21 S, surface 2.1 m(2)) and blood flow was kept between 300 and 400 mL/min. beta2-m concentrations were measured in plasma water and ultrafiltrate at appropriate times during a 240-minute treatment. The following dialytic parameters were calculated: total amount of beta2-m removed (A(tot)), beta2-m removed by convection (A(con)) and by adsorption (A(ads)), percent reduction in beta2-m plasma water concentration (% Cpw(in)), total plasma water clearance (CLpw(tot)), convective plasma water clearance (CLpw(con)), adsorptive plasma water clearance (CLpw(ads)), and sieving coefficient (SC)., Results: CLpw(tot), CLpw(ads), and% Cpw(in) were similar in pre- and postdilutional conditions, whereas CLpw(con) and SC were higher and CLpw(ads) was lower in postdilution than in predilution HF. Since a significant inverse correlation was found between A(ads) and SC, predilution probably determines greater protein fouling than postdilution., Conclusion: The 2 techniques appear to be equivalent in terms of total beta2-m removal, although this final result is obtained by different contributions of convective and adsorptive elimination.