VASCULAR REACTIVITY DURING COMBINED ULTRAFILTRATION HAEMODIALYIS - INFLUENCE OF DIALYSATE SODIUM

Background. It is well known that vascular reactivity is impaired duri ng combined ultrafiltration-haemodialysis as compared to isolated ultr afiltration and haemofiltration, which might be related to differences in plasma osmolality. Therefore vascular reactivity was studied durin g combined ultrafiltration-haemodialysis in relation to sodium-related differences in plasma osmolality/tonicity. Methods. With each patient serving as his or her own control, nine stable dialysis patients (23- 71 years) were studied during 2 h of combined ultrafiltration-haemodia lysis (bicarbonate; UF rate 1.0 l/h)) at two different dialysate sodiu m concentrations: 134 and 144 mmol/l. Before dialysis as well as every 20 min during dialysis, blood pressure (Dinamap), heart rate (EGG), a nd forearm vascular resistance and venous tone (strain-gauge plethysmo graphy) were measured. Relative blood volume was monitored continuousl y by an optical reflection method (Haemoguard 2000), while before and after dialysis blood was obtained for the estimation of plasma prostag landin E(2). Results. High-sodium dialysis resulted in a significantly higher post-dialysis plasma sodium concentration (139.9 vs 135.0 mmol /l; P<0.01) while the decrease in relative blood volume was significan tly smaller as compared to low-sodium dialysis (-8.4 vs -18.4%; P<0.01 ). There were no significant differences in the different haemodynamic parameters between the two treatment modalities. Both high- and low-s odium dialysis were associated with a significant increase in forearm vascular resistance while venous tone remained unchanged. Although the re was no significant difference in plasma PGE(2) between the two trea tment modalities, PGE(2) increased significantly only during low-sodiu m dialysis. We found no relationship between changes in PGE(2) and vas cular reactivity. Conclusions. We conclude that vascular reactivity du ring combined ultrafiltration-haemodialysis is not directly influenced by sodium-related changes in plasma tonicity. Although not directly s tudied, the reported improved haemodynamic stability with high-sodium dialysis is probably only mediated through a better preservation of pl asma volume. Finally, an increase in plasma PGE(2) as observed during low-sodium dialysis does not lead to a decrease in vascular tone.