Using invasive techniques we have studied various hemodynamic and gasometric parameters in the course of hemodialysis (HD) with different buffers in an animal model. HD sessions of 180 minutes at zero ultrafiltration were carried out on three groups of eight uremic dogs each, under anesthesia and constant mechanical ventilation. The three groups differed only in the buffer used: acetate (Group AC), equal proportions of DL-lactate and acetate (Group AC+LA), and bicarbonate (Group BC). No hemodynamic changes were seen in Group BC. In the AC and AC+LA groups we observed on minute 1 a decrease of the mean blood pressure (MBP) and of the systemic vascular resistances (SVR). These parameters returned to baseline values within the first 30 minutes in Group AC+LA. In Group AC the SVR also returned to baseline values after the minute 30, but the MBP remained below baseline throughout the study period, together with cardiac index and left ventricular stroke work index decreases. Only in Group AC did we see a flattening of the ventricular function curves. Only in this Group was there a decrease of the arterial oxygen pressure (PaO2) with an associated increase of the alveolo-arterial and arterio-venous O2 differences. The O2 consumption was not modified in any of the groups. Acetate as a single buffer induces hemodynamic instability through peripheral vasodilation and reduction of myocardial contractility. The myocardial depression induced by acetate, in its turn, causes a reduction in PaO2. The mixed acetate+lactate buffer is hemodynamically better tolerated than acetate as single buffer, as it induces only vasodilation.
Several abnormalities of porphyrin metabolism have been described in patients with end-stage renal failure. Because the heme biosynthetic pathway in acute renal failure has not been studied hitherto, an experimental model was therefore induced in 30 dogs by ligation and transection of both ureters. Forty-eight h after this procedure, anemia and uremia developed, erythrocyte aminolevulinate dehydratase activity decreased, and plasma porphyrins increased in these 30 dogs, whereas seven sham-operated animals did not exhibit any alteration of these parameters. Uremic plasma showed a capacity to inhibit aminolevulinate dehydratase activity (mean, 11.1 +/- 5.8%) when incubated in vitro with erythrocytes from healthy dogs. Such findings are similar to those reported in uremic patients on hemodialysis or on continuous ambulatory peritoneal dialysis. Twenty-three of the 30 animals underwent a hemodialysis session (180 min) 48 h after ureteral ligation, using a polyacrylonitrile membrane dialyzer. In addition to reducing serum creatinine and urea levels, this procedure significantly reduced plasma porphyrin values. However, the activity of erythrocyte aminolevulinate dehydratase and the plasma capacity to inhibit this enzyme were not modified after the hemodialysis session. This results described here show that some of the abnormalities of heme biosynthesis described in chronic renal failure are detected early in an experimental model of acute renal failure. This study also confirms that, although most plasma porphyrins circulate bound to proteins, hemodialysis may reduce levels of plasma porphyrins when a high permeability membrane is used.
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