The Role of Small-Molecule Removal in the Control of Treatment Morbidity with Hemodialysis and Hemofiltration

Abstract

In 1976, it was suggested that the critical factor in maintaining the blood pressure during isolated ultrafiltration (UF) was the stability of the serum osmolality, and that by inference the high incidence of symptomatic hypotension seen with efficient dialysis was due primarily to large drops in the serum osmolality.⁽¹⁾ A consequence of this ingenious study, limited to one series of acute experiments in only six selected patients, was the birth of the “shifters” school. The “shifters” believe that dialysis hypotension is due to hypovolemia during UF. The hypovolemia is exaggerated by the passage of extracellular fluid into the cells at the same time as it is removed from the body. Their conclusions are based on imprecise space measurements, and their results are often dubious.^(2,3) I have never believed in the “shifter” school and feel that Bergström and associates’ conclusions⁽¹⁾ could not apply in a chronic situation. To study this matter in more detail we selected six patients⁽⁴⁾ with a high incidence of symptomatic hypotension (drop in mean arterial pressure of more than 20% together with a requirement for nursing attention ± fluid replacement) during conventional hemodialysis lasting 4 hr and employing a 1-m² cuprophane dialyzer. The study was divided into three parts. Each part lasted for 1 month. During part 1, the dialysate flow rate (single pass) was 500 ml/min; in part 2, the dialysate flow rate was 300 ml/min; and in part 3, the dialysate flow rate was 100 ml/min. All other parameters were kept as near constant during all parts of the study.