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Dialysis
entry. On the venous end of the dialyser is a chamber designed to removed efficiently by HDF, and lower blood leptin levels have been
receive replacement fluid infusion and to reconstitute blood reported in long-term HDF patients.
22
OLHDF also reduces circulating
composition. Dialysate flows 50% countercurrent to blood and 50% levels of advanced glycosylation end products that have been implicated
concurrent with blood.
8
in the pathogenesis of both dialysis-related amyloidosis and
atherosclerosis.
23
These may all potentially favour the improvement of
Double High-flux Haemodiafiltration nutritional and cardiovascular status, although these clinical end-points
The double high-flux (DHF)HDF technique utilises two high-flux dialysers have not yet been evaluated in a rigorous manner.
in series: filtration in the proximal filter and backfiltration in the distal unit
(see Figure 1I). High blood flow and high efficiency enables treatment to Clinical Studies on Haemodiafiltration
take place within two hours.
9
Although HDF was first introduced decades ago, early evidence was not
sufficient to substantiate its widespread use. More recently, several
Push–Pull Haemodiafiltration comparative studies using one or more of the above techniques have
Alternating filtration and backfiltration, known as push–pull (PP)HDF, is yielded promsing results. A brief summary of the clinical effects of HDF
produced by alternating pre- and post-filter pumps. When the post-filter variants is presented.
pump is stopped, filtration occurs, and when the pre-filter pump is
stopped, the negative pressure induced in the blood compartment Intradialytic hypotension is the most common acute complication of HD,
produces backfiltration (see Figure 1J).
10
and has been associated with poor patient outcomes.
24,25
Twenty to 30%
of dialysis sessions are complicated by dialysis hypotension.
17,26
This is
Solute Removal with Haemodiafiltration believed to be due to rapid removal of solutes and fluids, particularly in
Dialysis adequacy is a strong independent factor associated with various patients at an increased risk. These include the elderly, diabetics and
outcomes in end-stage renal disease (ESRD). Among these are mortality, those with autonomic insufficiency and structural heart disease.
anaemia, nutrition and cardiovascular disease. European data from the Reduction in the frequency of this complication could contribute
Dialysis Outcomes and Practice Patterns (DOPPS) study demonstrated that significantly to improving the quality of life of patients and may even
patients on HDF achieved significantly higher Kt/V urea values compared improve outcome. Several observational studies suggest better
with patients who were receiving haemodialysis (HD).
11
Other studies intradialytic haemodynamic stability when patients were treated with
have also demonstrated that urea and creatinine removal are increased in convective therapies, including HDF.
14,26
high-efficiency OLHDF by 10–15% and maintained over time compared
with high-efficiency HD.
12–14
A meta-analysis of randomised controlled studies confirmed that systolic
blood pressure during dialysis was significantly higher and maximal drop
Although haemodiafiltration was
in systolic pressure was lower with convective modalities compared with
HD.
18
The precise mechanisms by which HDF maintains arterial pressure
first introduced decades ago, early
during dialysis are not completely understood. One possible factor is an
evidence was not sufficient to
increase in peripheral vascular tone and the vascular refilling rate due to
neutral thermal balance, particularly with high volume exchange.
26
Other
substantiate its widespread use.
factors that have been speculated about include the high sodium
More recent studies, however, have
concentration of the replacement fluid, release of vasoconstrictor
mediators, clearance of vasodilator mediators and improvement of
yielded promising results.
sympathetic activity.
HDF has also been shown to compare favourably with HD in terms of Dialysis-related amyloidosis (DRA) is a disorder caused by tissue
removal of various larger solutes. With the addition of convective solute deposition of β-2 microglobulin as amyloid fibrils. A registry study by
clearance, HDF enhances phosphate removal, reaching up to 30–35mM/ Locatelli et al. concluded that convective modalities including HDF and
session.
15
Patients on low-efficiency HDF had lower serum phosphate haemofiltration reduced the need for carpal tunnel surgery.
27
However,
levels compared with those on low-flux HD.
11
In randomised cross-over the beneficial effect of convective clearances per se in this study may
studies, phosphate levels were significantly lower with HDF.
14,16
As the have been partly confounded by the simultaneous improvement of other
calcium–phosphate product and vitamin D–parathyroid hormone axis factors. DRA is a difficult clinical end-point to evaluate adequately using
have recently been implicated as important factors associated with randomised studies as it takes years for the clinical and radiological
cardiovascular disease in ESRD patients, better phosphate removal manifestations of amyloidosis to appear. Moreover, there is a great deal
achieved with HDF may contribute to cardioprotection in this population. of variability in the clinical assessment of DRA. Clinical symptoms,
electromyography and X-rays have all been used to assess manifestations
Controlled trials have also shown a 20–30% greater reduction in of DRA, making it difficult to combine results from different studies
β-2 microglobulin per session with OLHDF than with high-flux HD. This looking at this outcome.
18
results in lower serum β-2-microglobulin levels sustained over time.
14,17,18
This may be relevant in reducing dialysis-related amyloidosis. Other larger Anaemia is an independent risk factor for left ventricular hypertrophy and
solutes that HDF appears to clear more efficiently include myoglobin and cardiovascular and overall mortality in dialysis patients, and also has an
retinal-binding protein
19
and protein-bound solutes such as p-cresol,
20
impact on quality of life. A number of studies suggest that anaemia was
homocysteine
21
and leptin.
22
HDF is hypothesised to remove protein- improved and recombinant human erythropoietin doses reduced in
bound forms or inhibitors of homocysteine metabolism.
21
Leptin is also patients treated with HDF.
11,16,28
Anaemia correction was also associated
56 EUROPEAN RENAL DISEASE 2007