Hemodialysis hemodynamics in an animal model: effect of using an acetate-buffered dialysate

Acetate-buffered dialysis (procedure A) was performed in conscious, nonuremic, splenectomized dogs. In some animals, dialysis was repeated after sympathectomy with 6-hydroxydopamine. During procedure A, hemodynamic changes were most pronounced 1 minute after starting dialysate flow (acute phase), and included a marked rise in cardiac output, pulse rate, and mean pulmonary artery pressure, but no change in mean arterial pressure (MAP) in intact animals. However, a precipitous fall in MAP was noted in sympathectomized dogs. Plasma acetate levels at this time averaged 2.0 +/- 0.5 mmol/L. Six to 30 minutes into procedure A, hypotension could be demonstrated in the intact, but not in the sympathectomized animals, at which time plasma acetate levels averaged 2.2 to 2.7 mmol/L. At 60 to 90 minutes into dialysis, when plasma acetate levels averaged 3.0 +/- 0.8 mmol/L, hypotension with procedure A was no longer significantly greater than with bicarbonate-buffered dialysis (procedure B). Plasma acetate levels at 30 to 90 minutes correlated with the change in cardiac output (r = 0.86, P less than 0.05) and total peripheral resistance (r = -0.76, P less than 0.05), but not with the decrease in MAP (r = -0.43, P not significant). Substantial hemodynamic changes were not seen when bicarbonate-buffered dialysis was used. Our results suggest that acute hypotension during procedure A in the dog model is prevented by an intact sympathetic nervous system. Hypotension occurring later during procedure A is difficult to demonstrate and does not appear to be accentuated after chemical sympathectomy. During procedure A the increase in cardiac output correlates with plasma acetate level.