Haemodiafiltration results in similar changes in intracellular water and extracellular water compared to cooled haemodialysis

Unveiling the Clinical Benefits of High-Volume Hemodiafiltration: Optimizing the Removal of Medium-Weight Uremic Toxins and Beyond

Dialysis treatment has improved the survival of patients with kidney failure. However, the hospitalization and mortality rates remain alarmingly high, primarily due to incomplete uremic toxin elimination. High-volume hemodiafiltration (HDF) has emerged as a promising approach that significantly improves patient outcomes by effectively eliminating medium and large uremic toxins, which explains its increasing adoption, particularly in Europe and Japan. Interest in this therapy has grown following the findings of the recently published CONVINCE study, as well as the need to understand the mechanisms behind the benefits. This comprehensive review aims to enhance the scientific understanding by explaining the underlying physiological mechanisms that contribute to the positive effects of HDF in terms of short-term benefits, like hemodynamic tolerance and cardiovascular disease. Additionally, it explores the rationale behind the medium-term clinical benefits, including phosphorus removal, the modulation of inflammation and oxidative stress, anemia management, immune response modulation, nutritional effects, the mitigation of bone disorders, neuropathy relief, and amyloidosis reduction. This review also analyzes the impact of HDF on patient-reported outcomes and mortality. Considering the importance of applying personalized uremic toxin removal strategies tailored to the unique needs of each patient, high-volume HDF appears to be the most effective treatment to date for patients with renal failure. This justifies the need to prioritize its application in clinical practice, initially focusing on the groups with the greatest potential benefits and subsequently extending its use to a larger number of patients.

Comparative Impact of Isolated Ultrafiltration and Hemodialysis on Fluid Distribution: A Bioimpedance Study

INTRODUCTION

Isolated ultrafiltration (IUF) is an alternative treatment for diuretic-resistant patients with fluid retention. Although hemodialysis (HD) predominantly decreases extracellular water (ECW), the impact of IUF on fluid distribution compared with HD remains unclear.

METHODS

We compared the effect of HD (n = 22) and IUF (n = 10) sessions on the body fluid status using a bioimpedance analysis device (InBody S10).

RESULTS

The total ultrafiltration volume was similar between HD and IUF (HD 2.5 ± 0.3 vs. ICF 2.1 ± 0.3 L/session, p = 0.196). The reduction rate of ECW was significantly higher than that of intracellular water (ICW) after HD (ECW -7.9% ± 0.8% vs. ICW -3.0% ± 0.9%, p < 0.001) and IUF (ECW -5.8% ± 0.9% vs. ICW -3.6% ± 0.8%, p = 0.048). However, the change in the ratio of ECW to total body water in HD was significantly larger than that in IUF (HD -3.2% ± 0.3% vs. ICF -1.1% ± 0.4%, p < 0.001). The reduction rates in serum tonicity (effective osmolality) were higher after HD than after IUF (HD -1.8% ± 0.5% vs. IUF -0.6% ± 0.2%, p = 0.052). Among the components of effective osmolality, the reduction rates of serum K+ and glucose levels after HD were significantly higher than those after IUF (serum K+: HD -30.5% ± 1.6% vs. IUF -0.5% ± 3.8%, p < 0.001; serum glucose: HD -15.4% ± 5.0% vs. IUF 0.7% ± 4.8%, p = 0.026), while the serum Na+ level was slightly and similarly reduced (HD -0.8% ± 0.4% vs. IUF -0.8% ± 0.4%, p = 0.500). The reduction in the osmolal gap value (measured osmolality-calculated osmolarity) was significantly greater after HD sessions than after IUF sessions (HD -12.4 ± 1.4 vs. IUF 2.0 ± 1.0 mOsm/kg, p = 0.001).

CONCLUSION

The extracellular fluid reduction effect of HD is stronger than that of IUF. The different changes in effective osmolality and osmolal gap after HD and IUF sessions may be related to the different effects of HD and IUF on fluid distribution.

Changes in extracellular water with hemodialysis and fall in systolic blood pressure

Introduction:

Intra-dialytic hypotension (IDH) remains the most common complication with outpatient hemodialysis (HD) sessions. As fluid is removed during HD, there is contraction of the extracellular volume (ECW). We wished to determine whether the fall in ECW was associated with a fall in systolic blood pressure (SBP).

Methods:

We retrospectively reviewed the records of adult dialysis outpatients attending for their midweek sessions who had corresponding pre- and post-HD bioimpedance measurements of ECW.

Result:

We reviewed 736 patients, median age 67 (54–76) years, 62.8% male, 45.7% diabetic with a median dialysis vintage of 24.4 (9.2–56.8) months. The percentage fall in ECW (ECW%) was associated with post-dialysis systolic blood pressure (SBP) (r = −0.14, p < 0.001). Patients with SBP falls of >20 mmHg had a greater fall in ECW% compared to patients with stable SBP 7.6 (4.6–10.1) vs 6.0 (4.0–8.5), p < 0.001). Patients with greater dialyzer urea clearance had greater fall in ECW% (r = 0.19, p < 0.001). In a logistic model an increased fall in ECW% was associated with weight loss (odds ratio (OR) 1.88, 95% confidence limits (CL) 1.62–2.176, p < 0.001), and session duration (OR 1.45 (CL 1.05–1.99), p = 0.024), and negatively with hemodiafiltration compared to hemodialysis (OR 0.37 (0.19–0.74) p = 0.005 and dialysate sodium to plasma gradient (OR 0.95 (CL 0.90–0.99), p = 0.021).

Conclusion:

We observed an association between the reduction in ECW and SBP with dialysis. Our results would advocate monitoring ECW changes during dialysis and developing biofeedback devices to control ultrafiltration and dialysate sodium to reduce the risk of IDH.

Clinical evidence on haemodiafiltration

Haemodiafiltration (HDF) combines diffusive and convective solute removal in a single treatment session. HDF provides a greater removal of higher molecular weight uraemic retention solutes than conventional high-flux haemodialysis (HD). Recently completed randomized clinical trials suggest better patient survival with online HDF. The treatment is mainly used in Europe and Japan. This review gives a brief overview of the presently available evidence of the effects of HDF on clinical end points, it speculates on possible mechanisms of a beneficial effect of HDF as compared with standard HD and ends with some perspectives for the future.

Enhancing dialyser clearance-from target to development

Products of metabolism accumulate in kidney failure and potentially have toxic effects. Traditionally these uraemic toxins are classified as small, middle-sized and protein-bound toxins, and clearance during dialysis is affected by diffusion, convection and adsorption. As current dialysis practice effectively clears small solutes, increasing evidence supports a toxic effect for middle-sized and protein-bound toxins. Therefore, newer approaches to standard dialysis practice are required to look beyond urea clearance. Current dialysers have been developed to effectively clear small solutes and secondly to increase middle-sized toxin clearances. However, there is no ideal dialyser which can effectively clear all uraemic toxins. Advances in nanotechnology have led to improvements in manufacturing, with the production of smoother membrane surfaces and uniformity of pore size. The introduction of haemodiafiltration has led to changes in dialyser design to improve convective clearances. Both diffusional and convectional clearances can be increased by changing dialyser designs to alter blood and dialysate flows, and novel dialyser designs using microfluidics offer more efficient solute clearances. Adjusting surface hydrophilicity and charge alter adsorptive properties, and greater clearance of protein-bound toxins can be achieved by adding carbon or other absorptive monoliths into the circuit or by developing composite dialyser membranes. Other strategies to increase protein-bound toxins clearances have centred on disrupting binding and so displacing toxins from proteins. Just as the hollow fibre design replaced the flat plate dialyser, we are now entering a new era of dialyser designs aimed to increase the spectrum of uraemic toxins which can be cleared by dialysis.

Haemodialysis and haemodiafiltration lead to similar changes in vascular stiffness during treatment

BACKGROUND

Haemodiafiltration (HDF) has been reported to cause less hypotension than haemodialysis (HD). We hypothesized that HDF causes less change in vascular tone, thereby reducing hypotension.

METHODS

Aortic pulse wave velocity (PWVao) was measured in 284 patients, during a single dialysis session using cooled dialysate (117 HD, 177 HDF). Patient groups were matched for age, sex and cardiovascular comorbidity.

RESULTS

Systolic blood pressure (SBP) declined from 144 ± 26 to 133 ± 26 after 20 minutes, and to 131 ± 26 mmHg post HD, and for HDF from 152 ± 26 to 143 ± 27 after 20 minutes, then to 138 ± 27 mmHg post HDF. Net Ultrafiltration rates to achieve weight loss were similar; HD 0.13 ± 0.06 vs HDF 0.12 ± 0.05 mL/kg/min. PWVao did not change after 20 minutes HD 0.42(-0.7 to 1.3), HDF 0.5 (-0.6 to 1.8) or at the end of the session: HD -0.39 (1.5 to 1.2), HDF -0.41(-2.0 to 1.3) m/s. Aortic augmentation index (AiAxo), assessment of vascular tone fell significantly with both HD; 20 minutes by 6.2 (-2.5 to 14), end 5.6 (-6.7 to 13.9), and HDF 20 min by 4.2 (-2.5 to 10), end 7.8 (-0.8 to 19.3), with no difference between HD and HDF. The ultrafiltration rate correlated with % change in aortic SBP (r = 0.28 p = 0.004), but not with changes in PWVao or augmentation indices.

CONCLUSIONS

Blood pressure declined during both HD and HDF treatments, as did augmentation indices, unrelated to weight loss, suggesting a reduction in vascular stiffness occurs independently of treatment modality. We did not observe an advantage for HDF.

Online-haemodiafiltration vs. conventional haemodialysis: a cross-over study

BACKGROUND

The main short-term advantages of haemodiafiltration (HDF) are supposedly better removal of Beta2-microglobulin (ß2-m) and phosphate, and better haemodynamic stability. The main disadvantage is higher costs. The aim of the study was to compare the clinical and biological parameters associated with HDF and high-flux haemodialysis (HD), using a cross-over design, while maintaining the same dialysis parameters.

METHODS

All patients on a 3 × 4 hours schedule were observed during 3 identical 6-months periods: HDF1 - HD - HDF2. The mean values for the 2 last months of each period were compared.

RESULTS

A total of 51 patients (76 % males, 45 % diabetic) with a mean age of 74 ± 15 years, and who had been on dialysis for 49 ± 60 months were included. The mean blood flow (329 ± 27 ml/min), dialysate flow (500 ml/min), and convection volumes (21.6 ± 3.2 L) were recorded. Patient medications were not changed. Predialysis blood pressure, phosphataemia, calcaemia, iPTH, Kt/V, nPNA and intradialytic events were similar throughout the 3 periods. Only serum albumin (34. 4 ± 3.6, 35.9 ± 3.4, 34.1 ± 4 g/L, p < 0. 0001) and ß2-m serum levels (26.1 ± 5.4, 28 ± 6, 26.5 ± 5 mg/L, p < 0.001, values shown for HDF1, HD, HDF2, respectively) were significantly lower during the HDF periods. Factor associated with higher delta serum albumin levels between HD and HDF periods was mainly a lower convection volume.

CONCLUSION

Comparing HDF and HD, we did not observe any differences in haemodynamic stability or in serum phosphate levels. Only serum ß2-m (-6% vs. HD) and albumin (-5% vs. HD) levels changed. The long-term clinical consequences of these biochemical differences should be prospectively assessed.

Does the presence of an arteriovenous fistula alter changes in body water following hemodialysis as determined by multifrequency bioelectrical impedance assessment?

Multifrequency bioelectrical impedance assessments (MFBIAs) aid clinical assessment of hydration status for hemodialysis (HD) patients. Many MFBIA devices are restricted to whole body measurements and as many patients dialyze using arteriovenous fistulas (AVFs), we wished to determine whether AVFs affected body water measurements. We reviewed pre- and post-HD segmental MFBIA measurements in 229 patients attending for midweek HD sessions. Up to 144 were dialyzed with a left arm AVF (L-AVF), 42 with a right arm AVF (R-AVF), and 43 by central venous access catheter (CVC). Water content and lean tissue were greater in the left compared to right arm in those patients with L-AVFs both pre and post dialysis (pre 2.1 ± 0.7 vs. 2.0 ± 0.7 L, and post 1.9 ± 0.6 vs. 1.8 ± 0.6 L and pre 2.65 ± 0.9 vs. 2.56 ± 0.8 kg, and post 2.34 ± 0.8 vs. 2.48 ± 0.8 vs. 2.34 ± 0.8 kg, respectively) and were also greater in the right compared to left arm for those patients dialyzing with R-AVFs (pre-HD 1.92 ± 0.5 vs. 1.86 ± 0.6 L and post-HD 1.79 ± 0.5 vs. 1.7 ± 0.5 L, and pre-HD 2.47 ± 0.6 vs. 2.38 ± 0.7 kg and post-HD 2.3 ± 0.74 vs. 1.28 ± 0.7 kg, respectively), all Ps < 0.05. There were no significant differences in arm volumes or composition pre or post dialysis in those dialyzing with CVCs. Segmental MFBIA detects differences in arm water and lean mass in patients with AVFs. The presence on an AVF increases the water content in the ipsilateral arm both pre and post HD. This increased water content of the fistula arm will not be detected by whole body bioimpedance devices.

Hemodiafiltration does not have additional benefits over hemodialysis on arterial stiffness, wave reflections and central aortic pressures

BACKGROUND/AIMS

The hypothesis that dialytic modality affects arterial stiffness was never investigated. This study includes comparative evaluation of hemodiafiltration versus hemodialysis on arterial function during first and second weekly dialysis sessions.

METHODS

24 patients receiving hemodiafiltration and another 24 age- and sex-matched controls receiving hemodialysis were included. Patients were evaluated before and after first and second weekly dialysis sessions. Applanation tonometry of peripheral arteries was applied to determine aortic and brachial pulse wave velocity and heart rate-adjusted augmentation index (AIx(75)).

RESULTS

Hemodiafiltration and hemodialysis reduced AIx(75), but not aortic and brachial pulse wave velocity. Intradialytic reductions in AIx(75) did not differ between hemodiafiltration and hemodialysis in first and mid-week dialysis. In multivariate linear regression, predictors of intradialytic reduction in AIx(75) were changes in body weight and central aortic systolic blood pressure, but not dialytic modality.

CONCLUSION

This study showed that hemodiafiltration has similar effects with hemodialysis on wave reflections and stiffness.