Dialysis, Ultrafi ltration, and Blood Pressure

overhydrated patients. This made it possible to relieve the uraemic patient from congestive heart failure and to control arterial blood pressure. Ultrafi ltration is generally applied continuously or intermittently, while the dialysis procedure (diffusion of substances across the dialysis membrane) is going on. During the last few years, short-time dialysis (3–4 hr 3 times a week or every other day) has proved to be successful in the treatment of patients with chronic uraemia [Cambi et al., 1974]. However, a limiting factor in reducing dialysis time is the inability to comfortably remove excess water and sodium in a very short time. One reason for this is that rapid ultrafi ltration during dialysis often leads to arterial hypotension assumed to be caused by hypovolaemia. Earlier observations in single patients at our dialysis unit suggested that rapid ultrafi ltration could be much better tolerated when performed without simultaneous dialysis than when dialysis was going on. This was seen for the fi rst time in a woman who easily reacted with arterial hypotension when ultrafi ltered during dialysis, but who could stand rapid ultrafi ltration without any fall in blood pressure when the dialysis fl uid (by mistake) bypassed the dialyser. More recent observations with the RP 6 dialyser and a recirculating system with 75 l of dialysis fl uid (Rodial) indicated that patients dialysed with this system could be more effi ciently ultrafi ltrated without discomfort and arterial hypotension than when treated with conventional single-pass dialysis [Man et al., 1973; own observations]. Summary The effect of ultrafi ltration on blood pressure was compared in six patients with problems of overhydration during single-pass dialysis, ultrafi ltration only (the fl uid bypassing the dialyser) and recirculation dialysis (using the RP 6 dialyser and the 75 l Rodial system). Adequate ultrafi ltration during single-pass dialysis was hampered by symptomatic hypotension. However, during recirculation dialysis as well as during ultrafi ltration without dialysis much more rapid ultrafi ltration was tolerated without a fall in blood pressure. A considerable fall in plasma osmolality occurred with single-pass dialysis, whereas only a small decrease occurred with recirculation dialysis and no change with ultrafi ltration only. We conclude that a rapid fall in plasma osmolality interferes with blood pressure regulation and that ultrafi ltration is far better tolerated provided that osmotic shifts are avoided or minimised.