Saudi Journal of Kidney Diseases and Transplantation

: 2011  |  Volume : 22  |  Issue : 5  |  Page : 982--989

Comparative study of perdialytic volemia variability in chronic dialysis patients between acetate- free biofiltration and bicarbonate hemodialysis

Kais Harzallah, Mayssa Daiki, Anis Baffoun, Mohamed Ben Salah, Mohamed Tagorti, Nourredine Hichri, Jalel Hmida 
 Unity of Hemodialysis, Military Hospital of Tunis, Tunis, Tunisia

Correspondence Address:
Kais Harzallah
Unity of Hemodialysis, Military Hospital of Tunis, Tunis, 1008


We have developed since 1994 a new hemodialysis (HD) technique called acetate biofiltration 84% (AFB 84%) that is characterized by the absence of acetate in the dialysate and the complete correction of buffer balance by post- dilutional infusion of bicarbonate- based replacement solution. Our study aimed to compare the variability of perdialytic volemia [net ultrafiltration (UF) rate, total UF, Δweight (T4- T0)] during AFB 84% and bicarbonate dialysis (BD) for stable chronic hemodynamic patients. This was a prospective crossover study carried out on 14 patients for a total of 168 HD sessions (84 AFB 84% and 84 BD). Optical measurement of hemoglobin (Hb) concentration was incorporated into the dialysis monitor to allow the study of the relative blood volume. For both techniques, Hb measured by Hemoscan® correlated well with the laboratory measurements. Moreover, the comparison of the averages of the different indicators of the perdialytic volemia did not disclose any significant statistical differences. Nevertheless, the comparison of the variability of perdialytic volemia between both techniques showed less Δ volemia (T4- T0) during the AFB 84% than the BD (- 7.909% for BD and - 6.960% for ABF 84%, P = 0.0036). We conclude that the absence of acetate and maintaining an optimal osmolarity at the origin of a better plasma refilling rate are key factors that make AFB 84% a technique assuring a better perdialyitic hemodynamic tolerance in comparison with BD in chronic HD patients.

How to cite this article:
Harzallah K, Daiki M, Baffoun A, Salah MB, Tagorti M, Hichri N, Hmida J. Comparative study of perdialytic volemia variability in chronic dialysis patients between acetate- free biofiltration and bicarbonate hemodialysis.Saudi J Kidney Dis Transpl 2011;22:982-989

How to cite this URL:
Harzallah K, Daiki M, Baffoun A, Salah MB, Tagorti M, Hichri N, Hmida J. Comparative study of perdialytic volemia variability in chronic dialysis patients between acetate- free biofiltration and bicarbonate hemodialysis. Saudi J Kidney Dis Transpl [serial online] 2011 [cited 2020 Oct 29 ];22:982-989
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Symptomatic dialysis hypotension occurs in up to 20% of dialysis session [1] and can lead to serious vascular problems such as stroke and myocardial or mesenteric infarction. [2],[3] It can also cause a state of chronic hyperhydration by inaccessibility and underdialysis. Consequently, prevention of dialysis hypotension arises as a priority for the dialysis team. [1],[2],[4]

The initial factor in the pathogenesis of dialysis hypotension is a decrease in plasma volume resulting from an imbalance between the ultrafiltration (UF) rate and the plasma refilling rate. [5] However, it is possible now to prevent dialysis hypotension by monitoring and maintaining the plasma volume of the patients during the dialysis session.

Since 1994, we have developed in our hemodialysis (HD) service a new HD technique titled acetate- free biofiltration 84% (AFB 84%). [6],[7] It is an extracorporeal blood purification technique that includes a buffer- free dialysate combined with infusion of sterile and non- pyrogenic solution of hypertonic 84% sodium bicarbonate at the venous return of the extracorporeal circuit [Figure 1]. Furthermore, it is now possible to perform the monitoring of plasma blood volume during HD by instantaneous measurement of the concentration of hemoglobin (Hb), performed by software (Hemoscan® ) integrated into the HD machine.{Figure 1}

The aim of our study was to compare changes in perdialytic blood volume during both techniques, AFB 84% and conventional hemodialysis with bicarbonate, in hemodynamically stable chronic HD patients based on changes in the levels of Hb measured by Hemoscan® .

 Materials and Methods

We studied 14 (seven men, seven women) chronic hemodialysis patients at the Military Hospital of Tunis who dialyzed three times a week. The mean age of the patients was 48.5 years (range from 26 to 76 years). The mean duration on HD was 4.45 years (range from 6 months to 12 years). Patients receiving rifampicin or having hemoglobinemia or myoglobinemia were not included in the study as these substances may interfere with Hb measurements with the Hemoscan® optical densitometer because of their similar optical wavelengths.

A single dialysis machine (Integra, Hospal®, Gambro) was used in this study for both the bicarbonate dialysis (BD) and the AFB 84% techniques. A Hospal® Bioline circuit with a special expansion chamber for Hemoscan® was also used. Cellulose triacetate dialysis filters (Nipro® 150) with a low- coefficient water permeability (6-10 mL/h/mmHg) and 1.5 m [2] surface area were used for both dialysis techniques.

In the sessions of AFB 84%, we used a concentrate for preparing the dialysate, especially prepared by the Tunisian Central Pharmacy (SIPHAT) in containers of 5 L. This buffer- free concentrate was made of a mixture of sodium chloride, potassium, calcium and magnesium.

Conductivity ranged from 13 to 13.5 mS/cm corresponding to a dialysate sodium concentration varying from 121 to 124 mEq/L. For conventional HD sessions, we used the usual acid and bicarbonate concentrate also provided by the SIPHAT. Conductivity ranged from 14.3 to 14.5 mS/cm, corresponding to a dialysate sodium concentration varying from 143 to 146 mEq/L.

Fluid replacement used for the AFB sessions was a sterile non- pyrogenic sodium bicarbonate 84% solution for intravenous injection. The total amount injected ranged from 3.5 to 4.5 mL/kg/h for a session of 4-6 hours without exceeding 1,500 mL/session. The injection of molar sodium bicarbonate is via a tube directly connected to the venous extracorporeal circuit venous chamber through an infusion pump, independent of the dialysis machine [Figure 1]. Substitution bicarbonate vials were maintained at room temperature.

Each patient received six successive sessions of BD and six successive sessions of AFB 84%, with a total of 168 sessions.

The parameters collected during the sessions included Hb blood levels, measured continuously by Hemoscan® . The Hb in the laboratory (HPLC method, diaSTAT automate) was also measured at time 0 (T0) and at time four hours (T4), hourly net UF in minutes, total net UF in hours and duration of the session in minutes. In addition, we calculated the Δ blood volume changes in blood volume during the session, expressed as a percentage of initial blood volume, Δ hemoglobin- Hb rate change during the session in g/dL and Δ weight- patient's loss weight in grams.

 Statistical Analysis

Statistical analysis of various collected data was performed using the SPSS 13.0 and Excel software. Comparison of the means was made using the Student "t" test for unpaired series. The significance level was set at P = 0.05, with the necessary use of interclass correlation coefficient and Cohen's Kappa. A very good match is set for a coefficient of over 0.81.


Regardless of the method of dialysis used and time of the measurement of Hb (T0 or T4), there was a very good interclass correlation coefficient between Hb measured by Hemoscan® and Hb measured in the laboratory [Table 1].{Table 1}

Indeed, this ratio was above 0.81 for both times T0 and T4 of the dialysis bicarbonate with r2 = 0.890 [Figure 2] and r2 = 0.884, respectively, [Figure 3]. It was also the same for the time T0 and T4 of AFB 84% session with r2 = 0.891 [Figure 4] and r2 = 0.895, respectively, [Figure 5].{Figure 2}{Figure 3}{Figure 4}{Figure 5}

Comparison of the means of the different indicators of perdialytic volemia subtraction (net UF, total UF and Δ weight) collected during the two techniques (hemodialysis bicarbonate (HDB) and AFB to 84%) showed no statistically significant difference. However, the comparison between the perdialytic blood volume change of the two techniques showed a highly significant difference with a smaller blood volume change for AFB 84% (- 7.909% for HDB and - 6.960% for the AFB 84%, P = 0.0036) ([Table 2], [Figure 6]).{Figure 6}{Table 2}


UF or convection, one of the physico- chemical principles of HD, is based on the subtraction of water from the vascular sector. During the HD sessions, monitoring is generally limited to basis weight and blood pressure. This results in a late therapeutic intervention limited to the onset of clinical symptoms. The ideal way to evaluate the plasma volume is based on dilutional methods using, e.g. human albumin labeled I- 131 or red blood cells labeled Cr 51. [8] Nevertheless, these methods are impractical in routine practice. The non- invasive methods of relative plasma volume measuring, however, allow for a real and repetitive relative plasma volume monitoring during the whole HD session. [9] These non- invasive means are currently of three types: optical, ultrasonic and electrical. The ultrasonic method uses the speed of propagation of ultrasound through the blood in the extracorporeal circuit. The electrical method is based on bio- electrical impedance, which uses the measurement of the resistance of fluid compartments of the body to estimate the fluid volume. Finally, the optical method is the most preferred type of monitoring of plasma volume (Hemoscan® ) in practice because of its easy use without the need for additional consumable materials. [10] The technique is based on measuring the optical density of blood flowing in the extracorporeal dialysis circuit using an optical cell inserted into the arterial line (arterial trap).

The percentage of change in plasma volume (relative to the initial blood volume) at time t using the formula: Vt = [(Hb0/Hbt) - 1 × 100] results from this basic measurement. Hb0 and Hbt represent the concentration of Hb at the beginning and at some point in the dialysis session. [8] These values appear in both digital and graphical mode using curves representing their evolution during the dialysis session. In our study, regardless of the dialysis method used and time of the measurement of Hb (T0 or T4), there was a very good interclass correlation coefficient between the Hb levels measured by Hemoscan® and those measured in the laboratory.

The plasma hypovolemia secondary to a rapid and high UF is probably one of the determining factors in the pathogenesis of per- dialytic hypotensive episodes. [11] In the ongoing effort to improve perdialytic hemodynamic tolerance, several techniques have been developed as AFB 14% and its variant AFB 84% described by Debure et al [12] in 1992 and developed by Hmida et al [6] in 1994.

Numerous studies have shown a significant reduction of hypotensive episodes during AFB 14% in comparison with BD. [13],[14],[15] Nevertheless, Duranti [16] found no significant difference in the reduction of blood volume between AFB 14% and BD.

Schrand et al have reported that the change in perdialytic blood volume is not the main factor in improving hemodynamic tolerance during the AFB 14%, but rather the absence of acetate. This hemodynamic instability is even more pronounced in older or malnourished patients or those who have abnormal left ventricular function, dysfunction of the autonomic nervous system or alteration of the metabolism of acetate (decreased muscle mass and liver failure). The perdialytic hypotensive episodes decreased significantly when acetate was replaced by bicarbonate in the dialysate. However, even in this case, a minimal amount of acetate, from 4 to 10 mEq/L, is always present in the dialysis circuit. This small amount is essential to maintain the dialysate stability by avoiding the formation of calcium carbonate and magnesium crystals, but it may be the cause of hemodynamic instability, especially in patients with limited cardiovascular function or with impaired metabolism of acetate. [18] Hmida et al reported a better hemodynamic tolerance of AFB 84% compared with HDB, but it was carried out in the absence of perdialytic blood volume monitoring. [19] Through this study, we tried to find an explanation for this better hemodynamic tolerance. The slightest drop in perdialytic blood volume unrecognized during the AFB 14% and the absence of acetate could be the key to the better hemodynamic tolerance of AFB 84%. The maintenance of optimal plasma osmolarity by continuous injection of molar sodium bicarbonate could be the origin of the lesser decrease in plasma volume expansion during the AFB 84%. It provides, in the early hours of dialysis, [6],[19] a serum sodium concentration within the physiological range, but remaining higher than that observed during the BD. Indeed, during the AFB 84%, serum sodium concentration undergoes a rapid rise during the first two hours of the dialysis session, whereas during BD, although using a high concentration of sodium in the dialysate, the serum sodium concentration reaches the optimal threshold only during the last hour. [6] Moreover, changes in perdialytic serum sodium concentration during the AFB 84% can maintain a higher plasma osmolarity than cell osmolarity, and the effect of a rapid decline of plasma urea concentration by the diffusive component of the dialysis is compensated by the elevation of serum sodium concentration. [6] Because sodium is the main extracellular cation, it has an essential role in maintaining blood osmolarity. Therefore, changes in plasma sodium concentration cause fluid movements across cells to maintain osmotic balance between the different compartments and, consequently, ensure hemodynamic stability. [20],[21],[22] Furthermore, the kinetics of the perdialytic sodium serum concentration during the AFB 84% probably allow a better distribution of water volume in favor of the vascular compartment avoiding the transfer of water into the cell in case of extracellular hyposmolarity ("water shift" or pirate UF) and keeping a reserve of water in the interstitium used for vascular filling ("Plasma Refilling rate") during the UF preventing, thus, the occurrence of hypovolemia.

On the contrary, in BD, fluid subtraction by UF is accompanied by a decrease in hydrostatic pressure and an increase in oncotic pressure of the vascular area, leading to "Plasma Refilling rate," which compensates the water loss caused by vascular UF. [23],[24] The diffusive component of the different dialysis techniques, such as BD, causes a decrease in plasma osmolarity by rapid purification of urea at the extracellular space as it is osmotically active in chronic renal failure patients. [25],[26],[27] This decrease in osmolarity may be increased if the dialysate sodium level is lower than the perdialytic serum sodium concentration. As a result, a double loss of sodium is produced by both UF and diffusion, contributing, consequently, to a significant decrease in perdialytic and interstitial sodium concentration. These two factors are responsible for "water shift," causing cell swelling and decreased volume of the interstitial compartment. [20],[27] The resulting decrease in both volume and pressure of the interstitial compartment is responsible for a decrease in the "Plasma Refilling rate," exacerbating hypovolemia. [28] When we used a dialysate sodium level below the plasma sodium level, Oh et al [30] demonstrated that if 3.5 L of water leave the extracellular compartment during a dialysis session, only 2.5 L constitute the UF, and 1 L passes through the cells. This explains why the fall in blood pressure may persist even after cessation of UF. This phenomenon is more marked in patients whose hemodynamic status is precarious. Thus, the use of a technique of extracorporeal purification capable of maintaining optimal plasma osmolarity, such as AFB 84%, results in cancelling or even reversing the "water shift" and reduces hypovolemia. [26],[27],[31]

In conclusion, the study of the perdialytic variation of plasma volume expansion shows that despite a moderate UF rate and comparable moderate weight losses, the reduction of plasma volume expansion at the end of sessions was significantly higher in DB compared with AFB 84%. The absence of acetate and the maintenance of optimal osmolarity at the origin of a better "Plasma Refilling rate" render the AFB 84% a better technique for perdialytic hemodynamic tolerance than BD in chronic HD patients.


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