CARDIOVASCULAR-RESPONSE DURING HEMODIALYSIS AND HEMOFILTRATION - THERMAL, MEMBRANE, AND CATECHOLAMINE INFLUENCES

Nine patients on regular dialysis were studied, in a cross-over format comparing hemodialysis (HD) and hemofiltration (HF), to identify pote ntial mechanisms of the disparate hemodynamic responses. Dialysis and substitution fluid composition (high sodium, acetate), treatment time, fluid loss rate, and membrane type (AN 69) were matched. Cardiac outp ut was determined by changes in thoracic electrical bioimpedance. Card iac output remained stable during HF but increased during HD (p < 0.00 1, HD vs. HF), despite a parallel reduction in stroke volume. The hear t rate response was significantly greater during HD relative to HF (p < 0.01). Systemic vascular resistance remained stable during HF but de creased significantly during HD (p < 0.05). Although there was a modes t fall during HD, the difference in blood pressure at the end of treat ment between HD and HF was not significant. Comparable increases in bo dy temperature were observed during both treatments. Plasma catecholam ines increased in parallel during HD and HF and following orthostatic stimulation at the end of treatment, and extracorporeal catecholamine clearances were similar. The values for serum sodium, total CO2, anion gap, potassium, and hematocrit at the end of treatment were similar, whereas total serum calcium was significantly greater following HD. Th ere were no significant differences in indices of myocardial contracti lity or central blood volume. These results suggest that the disparate hemodynamic responses to fluid and solute removal during HD and HF ca n be dissociated from changes in osmolality or venous tone, membrane b ioincompatibility, thermal stress, or differences in acetate delivery or catecholamine release. The explanation for the disparate hemodynami c responses between these two treatment modalities remains unclear. A role for an as yet unidentified vasodilatory substance generated durin g dialysate exposure, or convectively removed during hemofiltration, r emain intriguing possibilities.