**2. Description of the AFB technique**

Acetate Free Biofiltration (AFB) is a haemodiafiltration technique (combining diffusion and convection) that uses a dialysate without acetate or bicarbonate, and in which postdilution sodium bicarbonate is infused (145 or 167 mmol/L) throughout dialysis (Santoro et al., 2007) (Figure 1).

The primary characteristic of this haemodialysis technique is the absence of acetate. It must be taken into account that in conventional bicarbonate haemodialysis we continue to use 4 mmol/L of acetate to stabilise the acid part of the dialysate. This leads serum acetate levels to increase in conventional bicarbonate haemodialysis. Acetate is not used in AFB.

The advantages of this technique comprise improved haemodynamic stability and a reduction in the number of hypotensive episodes (Cavalcanti et al., 2004), the correction of metabolic acidosis, and improved clearance versus conventional haemodialysis (Santoro et al., 2007). Haemodynamic stability is improved by avoiding acetate (related to cytokine production, vasodilation and negative inotropic action); a solution is supplied with a high sodium content in reinfusion throughout dialysis (thereby improving vascular filling) (Tsutomu et al., 2011); the temperature is lowered (through sodium bicarbonate reinfusion at room temperature); and convection is employed (this involving the use of highly-

though symptomatically it is very well tolerated. Dialysis with low K content in the dialysate adequately reduces patient hyperkalaemia, but proves highly arrhythmogenic and is poorly tolerated by the patients. With AFB-K we are able to adequately reduce hyperkalaemia without causing arrhythmia, since blood K is gradually reduced. The patients who stand to benefit most from this dialysis technique are those with significant

**Blood entry Blood entry**

Arrhythmias are very common in patients with CRF undergoing dialysis, and they are the cause of a significant percentage of sudden deaths of cardiac origin (Meier et al., 2001). Arrhythmias are more common in certain groups of patients: subjects with heart disease, left ventricular hypertrophy, coronary disease, heart valve disorders, high blood pressure or

Na Ca K Mg

Na Ca K Mg

+ ++ + ++

> GLUCOSE H2 O

GLUCOSE O

Cl-

Cl -

**Dialisate without tampon Dialisate without tampon**

**Dialysate without buffer**

H2O

H2 O

> K +

K+ No K+

No K+

**Dialisate Dialisateexit**

**Dialysate exit**

Haemodialysis causes an arrhythmogenic effect (Meier et al., 2001). Dialysis is known to be related to QT prolongation in the ECG tracing (this being a risk marker for serious

Arrhythmia in dialysis may be related to sudden ion or blood pressure fluctuations. K+ is a particularly arrhythmogenic ion (Kovesdy et al., 2007), related to the membrane potential, which is involved in cardiac cell depolarisation. K+ experiences sudden changes during haemodialysis, and a sharp drop can induce arrhythmia (Cupisti et al., 1999). In some cases, and despite diet advice or medical therapy, patients arrive for their dialysis session with high serum K+ levels, and experience a sudden decrease during the early part of the session. This has been related to the appearance of arrhythmias or to the worsening of pre-existing arrhythmias: induction or worsening of ventricular extrasystoles, QT prolongation (Cupisti

comorbidity and therefore with an increased risk of suffering arrhythmia.

**Blood exit Blood exit**

**-**

**Na <sup>+</sup> HCO <sup>3</sup>**

**Infusion Infusion** 

Fig. 2. AFB-K dialysis circuit.

**Patient Patient**

diabetes, and elderly patients.

**4. Arrhythmia in patients on dialysis** 

ventricular arrhythmia) (Genovesi et al., 2003).

permeable biocompatible membranes). These advantages prove more evident in patients susceptible to suffering hypotension during dialysis, such as diabetics or elderly subjects with autonomous nervous system disorders, heart disease or liver disease, and subjects with significant comorbidity (Tsutomu et al., 2011, Sato et al., 2011). In a literature review, Santoro et al. (Santoro., 2007) described a reduction in hypotension events in AFB vs bicarbonate haemodialysis: the probability of intradialysis hypotension with AFB was reported to be close to 40% of the probability of intradialysis hypotension in the case of conventional bicarbonate haemodialysis. **Patient** Acetate Free Biofiltration with Potassium Profiled Dialysate (AFB-K) 229

Fig. 1. AFB dialysis circuit.
