Cardiovascular response to hemodialysis: the effects of uremia and dialysate buffer

Cardiovascular instability continues to be one of the primary clinical problems in hemodialysis. Acetate buffer in dialysate is one of the factors that may induce hypotension. Since uremia may have a direct effect on the regulation of the cardiovascular system, the present study was designed to investigate the separate effects of uremia and acetate hemodialysis on blood pressure in anesthesized dogs, as well as the hemodynamic parameters determined by invasive cardiovascular monitoring. Animals were separated into four groups: (1) group I, hemodialysis with acetate in controls; (2) group II, hemodialysis with acetate in uremic dogs; (3) group III, hemodialysis with bicarbonate in controls; and (4) group IV, hemodialysis with bicarbonate in uremic dogs. Acute uremia was induced by bilateral ureteral ligation and a 90-minute hemodialysis (acetate or bicarbonate) procedure was performed 72 hours later. The results obtained in this study show that, compared with dogs with normal renal function, acute uremia resulted in an elevation in mean arterial pressure (MAP; 178 +/- 13 vs. 115 +/- 23 mm Hg, P < 0.01), which was associated with an increase in cardiac index (CI) and left ventricular stroke work index (LVSWI). In these dogs, the pulmonary capillary wedge pressure (PCWP; preload) and the systemic vascular resistance index (SVRI; afterload) were not different than controls. In uremic dogs, hemodialysis with acetate, but not with bicarbonate, decreased the MAP to values similar to controls. The decrease in MAP induced by acetate hemodialysis in uremic dogs was associated with a decrease in SVRI and PCWP. These results suggest that in dogs with acute uremia, acetate hemodialysis (HD) decreases myocardial contractility that was previously increased by a direct effect of uremia. In controls, acetate produced a moderate decrease in MAP that was the result of a mild decrease in CI and SVR. Since PCWP was not significantly decreased after acetate HD, the decrease in CI can be attributed to a mild decrease in myocardial performance. In conclusion, this study in dogs suggests that uremia enhances myocardial contractility directly. Acetate hemodialysis reduces this elevated myocardial contractility to normal values.