Fluid balance during haemodialysis and haemofiltration: the effect of dialysate sodium and a variable ultrafiltration rate.

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half: 146 mmol/l) (HDS), and (3) with the same variable dialysate sodium and an ultrafiltration profile (two-thirds was withdrawn during the first half of treatment, the remainder during the second half) (HDSU).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.

The influence of dialysate sodium and variable ultrafiltration on fluid balance during hemodialysis.

An important factor in the development of hypotension during hemodialysis (HD) is a decrease in blood volume, due to ultrafiltration (UF) and an insufficient refill of the intravascular compartment. This insufficient refill might be caused by a transcellular fluid shift from the extracellular to the intracellular compartment. We studied the influence of dialysate sodium concentration and UF rate on the refill rate, blood volume, intracellular (ICV) and extracellular fluid volume (ECV). Three different HD strategies were studied in 15 patients: (A) conventional HD (dialysate sodium 140 mmol/L); (B) HD with a sodium profile (140-148 mmol/L); and (C) HD with a sodium profile and a variable UF rate (high-low UF rate). ICV and ECV were measured by non-invasive conductivity measurements, blood volume was calculated from erythrocyte counts before and after treatment. Blood volume decrease was most pronounced during conventional HD, due to insufficient refilling without a detectable transcellular fluid shift. The sum of the decrease in ICV and EVC was less than during (B) and (C). The insufficient refill led to a higher prevalence of hypotension and cramps. The strategies (B) and (C) led to an significant and comparable transcellular fluid shift to the extracellular compartment. Thus, the use of a sodium profile led to a better intravascular refill and clinical tolerance of HD. Addition of a UF profile did not improve this any further.

How to prevent vascular instability: haemofiltration.

Most investigators agree that the remarkable tolerance of the vascular system to fluid withdrawal by haemofiltration is one of the most important advantages of this method. On the other hand it has been shown that blood pressure can be normalised in patients with dialysis-resistant hypertension by applying haemofiltration. The preservation of extracellular osmotic pressure during haemofiltration, obviously caused by the maintenance of a relatively high extracellular Na+ concentration, may induce a rapid and effective refilling of this compartment thus preventing vascular instability. A concept which may explain the apparently contradictory effect of haemofiltration on hypo- and hypertension, is proposed.

Response of the vascular system to different modifications of haemofiltration and haemodialysis.

In order to evaluate the reasons for the better tolerance of the cardiovascular system to body fluid removal in HF, different modifications of single-pass and recirculation HD as well as post-dilution HF were applied in 6 patients with stable chronic renal insufficiency under identical conditions of fluid removal, Curea and use of dialysers. A remarkable tolerance of the vascular system could be observed in HF as in HD when the Na+ concentration in the dialysis or diluting fluid was raised from 130 to 150mEq/L or when plasma osmotic pressure was stabilised by i.v. infusion of mannitol. The different buffers acetate and lactate did not influence the results specifically. Total peripheral resistance and plasma noradrenaline levels increased in HF but showed no changes in HD. Important factors causing the greater tolerance of the cardiovascular system in HF may be a more stable extracellular osmotic pressure, inducing a rapid refilling of the extracellular space, combined with an increasing total peripheral resistance.

Clinical and technical aspects of hemofiltration.

The removal of uremic substances in hemofiltration, in contrast to hemodialysis, is achieved by means of a convective transport across membranes of high porosity. Since 1974, more than 30 patients with chronic renal insufficiency have been treated with regular hemofiltration three times weekly for four to five hours each. After completing a pilot study, a controlled study to compare hemodialysis and hemofiltration was initiated during January, 1978. A normalization of blood pressure in patients with severe hypertension, and remarkable stability of the circulatory system, even after dehydration in patients who had hypotension in spite of fluid overload, could be demonstrated. Hemofiltration is preferred, especially in older patients with cardiovascular or cerebrovascular problems, because of its lower frequency of hypotensive episodes compared to dialysis. An important aim--the miniaturization of the artificial kidney--has not yet been achieved, however, because of the necessity for an extensive monitoring system for the exact proportioning of the sterile substitution fluid. First results in the application of a fluid regeneration system consising of a charcoal cartridge and a bioelectric cell, for degradation of urea, are presented.

Haemo- and peritoneal dialysis treatment of patients with diabetic nephropathy--a comparative study.

Thirty-two patients with advanced chronic renal insufficiency due to juvenile onset diabetes mellitus were submitted to dialytic treatment, 16 with intermittent haemodialysis and 16 with peritoneal dialysis. Both groups were similar with respect to onset of diabetes, course of renal insufficiency, as well as start and duration of dialysis treatment (382 and 389 patient months respectively). Patients on haemodialysis showed a more rapid progress of retinopathy and neuropathy, whereas the control of hypertension proved to be more difficult with peritoneal dialysis. A reduced peritoneal dialysance of urea, demonstrated in patients with diabetic nephropathy, could be improved by dipyridamole administration, whereas this drug showed no effect on the dialysances of urea and inulin in patients with chronic renal insufficiency of non-diabetic origin. There were no differences between the survival rates of the two groups which were substantially lower than in non-diabetic dialysis patients.

Hemofiltration: treatment of renal failure by ultrafiltration and substitution.

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.

Treatment of severe hypertension in chronic renal failure by haemofiltration.

Thirteen patients with chronic renal insufficiency who had been transferred from haemodialysis to haemofiltration treatment because of dialysis and drug resistant hypertension (10 with high plasma renin activity) showed normalisation of blood pressure during a treatment period of 8 months, after which only one patient required antihypertensive drug therapy. During the first period blood pressure drop paralleled body weight loss and after 3--4 weeks blood pressure remained normal in spite of an increase in body weight. In the course of the second phase the effect of fluid withdrawal on blood pressure was directly proportional to the blood pressure at the beginning of the procedure. Adaptation of baroreceptor function must be assumed. In contrast to haemodialysis, haemofiltration did not influence the inulin space. Because of the reduced removal of small molecular substances compared with haemodialysis, extracellular osmolarity was kept stable during haemofiltration. Withdrawal of even large amounts of fluid was sustained without collapse reactions or signs of orthostatic dysregulation.