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 f actors that may induce hypotension. Since uremia may have a direct eff ect 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 h emodynamic parameters determined by invasive cardiovascular monitoring . Animals were separated into four groups: (I) group I, hemodialysis w ith acetate in controls; (2) group II, hemodialysis with acetate in ur emic dogs; (3) group III, hemodialysis with bicarbonate in controls; a nd (4) group IV, hemodialysis with bicarbonate in uremic dogs. Acute u remia was induced by bilateral ureteral ligation and a 90-minute hemod ialysis (acetate or bicarbonate) procedure was performed 72 hours late r. The results obtained in this study show that, compared with dogs wi th normal renal function, acute uremia resulted in an elevation in mea n 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 v entricular stroke work index (LVSWI). In these dogs, the pulmonary cap illary wedge pressure (PCWP; preload) and the systemic vascular resist ance index (SVRI; afterload) were not different than controls. In urem ic dogs, hemodialysis with acetate, but not with bicarbonate, decrease d the MAP to values similar to controls. The decrease in MAP induced b y acetate hemodialysis in uremic dogs was associated with a decrease i n SVRI and PCWP. These results suggest that in dogs with acute uremia, acetate hemodialysis (HD) decreases miocardial contractility that was previously increased by a direct effect of uremia. In controls, aceta te produced a moderate decrease in MAP that was the result of a mild d ecrease in CI and SVR. Since PCWP was not significantly decreased afte r 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 hemodi alysis reduces this elevated miocardial contractility to normal values .