One of the main causes of hypotension during extracorporeal renal replacement therapy is an insufficient substitution of the ultrafiltrated plasma water by tissue water. To investigate the fluid balance and its effects on hypotension in dialysed patients, the following variables were studied: intracellular fluid volume (IFV) and extracellular fluid volume (EFV), blood volume (BV) and blood pressure. IFV and EFV were measured by means of non-invasive electrical conductivity measurements using four electrodes round the leg. Fifteen haemofiltration (HF) and 15 haemodialysis (HD) patients were studied. The latter group was dialysed in three ways: (1) conventionally, i.e. with dialysate sodium of 138 mmol/l (HD) (2) with a variable dialysate sodium (first half: 138 mmol/l; second half: 146 mmol/l) (HDS), and (3) with the same variable dialysate sodium and an ultrafiltration profile (two-thirds was withdrawn during the first half of treatment, the remainder during the second half) (HDSU). Hypotension frequency was less during HDS, HDSU, and HF compared to HD. This was caused by a more stable blood volume due to a better refill. During HD a fluid shift occurred from the EC to the IC compartment. The use of a high sodium dialysate concentration led to a transcellular fluid shift in the opposite direction. This fluid shift increased the refill, thereby stabilising blood volume. HF gave a better refill than HDS and HDSU, probably due to a reduced urea clearance.

Hemofiltration, in contrast to hemodialysis or peritoneal dialysis, eliminates toxic substances accumulated in uremia by a process that is independent of molecular weight. By means of a special device, the ultrafiltrate of blood is replaced, up to the desired amount, by a modified Ringer's lactate solution. The application of this new method results in better control of severe hypertension, and controls calcium phosphate and lipid metabolism in a more physiologic manner than dialysis does, without additional drug therapy being necessary. Smaller amounts of fluid and a simplification of devices improve hygienic conditions and patient mobility.

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Long-term survival and morbidity in regular hemofiltration treatment is evaluated in two groups of patients with chronic renal insufficiency bearing different categories of risk. In one group of patients with low-risk (restriction of age, exclusion of diabetes mellitus and vascular diseases), complications during regular hemofiltration treatment (115 patients, 5,196 patient months) are compared to those of regular hemodialysis treatment (132 patients, 6,690 patient months). In a second group of patients with ‘high-risk’ (inclusion of diabetic nephropathy and cerebro- or cardiovascular diseases), hemofiltration (57 patients, 1,428 patient months) is compared to continuous ambulatory peritoneal dialysis (CAPD; 68 patients, 1,464 patient months). Long-term survival rates (8 years in the first and 5 years in the second group) did not show significant differences for hemofiltration and hemodialysis in the first group or for hemofiltration and CAPD in the second one. Main reasons for death in both groups were cardiovascular or cerebrovascular complications, and in the CAPD group infections (peritonitis, pneumonia), being similarly significant. Important differences between hemofiltration and hemodialysis on the one hand, and hemofiltration and CAPD on the other, could be demonstrated concerning morbidity, expressed in days of hospitalization per months of treatment. Hypotension, cardiovascular and cerebrovascular diseases, especially, necessitated significantly less frequent hospitalization of hemofiltration patients than of hemodialysis or CAPD patients; main reasons for hospitalization of hemodialysis patients being fistula complications and hypertension and for CAPD patients being infection, cardiac insufficiency, cerebrovascular disease and hypotension. In the second group, the frequency of complications of diabetes mellitus (retinopathy, angiopathy) was significantly higher in hemofiltration than in CAPD treatment. As has been shown earlier for short-term treatment, hemofiltration may exhibit its main advantage over hemodialysis in patients suffering from vascular complications also with long-term observation, thus ameliorating the quality of treatment.