Conventional hemodialysis (HD) is essential for the treatment of end-stage renal disease (ESRD) patients, by reducing serum concentration of uremic toxins and correcting fluid overload.

Nevertheless, HD removes almost exclusively low-range uremic toxins. Therefore, medium-range molecules, such as beta-2-microglobulin might accumulate in tissues, leading to many clinical complications, such as neuropathies, tendinopathies, anemia, bone mineral disease and reduced growth in children.

Convective methods might reduce incidence of these complications, by removing molecules of medium-range molecular weight. Online hemodiafiltration (olHDF) is the most extensively used method in this regard. Nevertheless, there are some barriers to the wider introduction of this method in clinical practice, since specific machines are needed for this procedure, the costs with dialysis lines are higher and water consumption increases. More recently, the development of new membranes for hemodialysis allowed removal of medium- and high-range uremic toxins, with albumin retention. Thus, they allow removal of a broad range of uremic toxins, without changing dialysis machine or increasing water consumption. Such therapy is known as expanded hemodialysis (HDx).

The aim of this present study is to compare the extraction of middle-size molecules, the hemodynamic behavior, fluid and nutritional status of patients submitted to olHDF or HDx, in a crossover study.

Hypothesis

Our hypothesis is that HDx is noninferior to olHDF in the following parameters:

• Hemodynamic stability
• Nutritional and fluid status
• Removal of beta-2 microglobulin

Objectives To evaluate each patient, through a prospective, randomized and cross-over study, the intradialytic hemodynamic behavior, fluid and nutritional status assessed by electrical bioimpedance and B2M removal in two dialytic modalities: HDFol versus HDx.

Concise methods

1. Clinical and laboratorial data Clinical data will be collected from the institution's chart, recorded and filled with all necessary precautions to keep confidentiality of patient's information. They are: baseline renal disease, age, history of smoking, sedentary lifestyle, presence of comorbidities such as hypertension and diabetes mellitus, family history of cardiovascular disease, history of coronary and cerebrovascular disease and medications.

   Laboratory tests used to determine the biochemical, hematological and bone mineral profile characteristics will be obtained from routinely collected exams. Such exams are processed by the Central Laboratory of Hospital das Clínicas / FMUSP.

2. Dialysis All dialysis procedures will be performed by the Dialog+ Admea™ machine (BBraun Melsungen AG, Germany).

   The olHDF will be prescribed as follows: blood flow 350 - 400 ml/min, dialysate flow 800 ml/min, post-dilution flow (90-100 ml/min), with high-flux Xevonta™ (BBraun Melsungen AG, Germany) or CAHP/DICE™ (Baxter Healthcare Corporation, Germany) dialyzers, with surface area of 1.7-2.4 m². The duration of each session will be from 3,5h to 4h, depending on current dialysis prescription. Total substitution volume will be higher than 20 L per session.

   HDx will follow the same prescription of olHDF, regarding blood and dialysate flows and dialysis duration. There will be no substitution volume. Theranova™ dialyzers (Baxter Healthcare Corporation, Germany) will be used for each session.

   Before initiating protocol and during the washout period, patients will be submitted to high-flux HD, which is the standard treatment in our service.

3. Hemodynamic monitoring Cardiac output index (CI), stroke volume (SV - integrated mean of the flow waveform between the current upstroke and the dichotic notch), peripheral arterial resistance (PAR - ratio of mean arterial pressure to stroke volume multiplied by heart rate) and blood pressure (BP) will be accessed by finger beat to-beat monitor Finometer™ (Finapress Medical Systems BV, Arnhem, The Netherlands), within 15 minutes after starting olHDF or HDx sessions (predialysis) and again, 15 minutes before its end (post-dialysis).

4. Bioelectrical impedance Segmental tetrapolar bioelectrical impedance (BIS) will be performed in all patients while recumbent, before starting study protocol and before each phase of the study (HDx or olHDF), by the multifrequency InBody™ S10 (Biospace Co., Ltd., Korea) device. It allows assessment of the following parameters regarding body fluids: total body water, total extracellular body water, lower limbs total water content, lower limbs extracellular water content. Additionally, α-angle, which is a marker of cellular integrity and nutritional status, will be noted.

5. Blood and Effluent samples Blood samples will be collected pre-session, mid-session and post-dialysis sessions, both in the first and last dialysis sessions of each of the periods studied (HDFol or HDx). Pre-session blood samples will be collected immediately after arteriovenous fistula puncture and the middle and post-session samples will be collected from the arterial line, 2 minutes after reduction of blood flow to 50 ml/min and suspension of dialysate flow and/ or replacement.

In addition, partial and homogeneous collection of the effluent will be performed by a drainage hose, with an infusion pump operating continuously at a rate of 1l/h. The whole effluent of dialysis session will be collected.

Inclusion Criteria:

• Adult patients who are on maintenance hemodialysis at Hospital das Clínicas and agree to participate in the study by signing the informed consent form.

Exclusion Criteria:

• Patients who cannot understand or who refuse to sign the informed consent form; Patients who are currently on daily hemodialysis or online hemodiafiltration.

3 months

No adverse events noted

The sample size was small and trial length was relatively short. We did not directly assessed albumin extraction. Besides, the relatively low ultrafiltration coefficient of both dialyzers limited dialysis performance in all treatment groups.

Investigator who collects laboratorial, hemodynamics and bioimpedance data will be blinded for intervention (online hemodiafiltration or expanded hemodialysis)