**2. Plasma exchange: basic principles**

Generally, in PEX, blood is pumped out of the patient's circulation and is transferred to the filter, separating plasma from blood cells. Afterwards, blood cells are pumped into the patient's vein. Patient's plasma is substituted by human albumin and/or FFP.

> © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### **2.1. Vascular access**

In most of the cases, central venous catheters are used in PEX, especially in acute conditions. They can be placed in internal jugular, femoral and subclavian veins. However, if life-long treatment is needed (e.g., LDL apheresis), arteriovenous fistula creation may be required. In addition, as the blood flow is low (90–150 ml/min), large peripheral veins can be used (cubital veins). Single-vein access is also possible but in cases where centrifugal separation of plasma is used.

*2.2.3.2. Cryofiltration*

*2.2.3.3. Thermofiltration*

*2.2.3.4. Unselective adsorption*

*2.2.3.5. Selective adsorption*

(HUS) and so on.

again and is returned to the patient.

molecules after being exposed to higher temperatures [2].

improved effectiveness and improved safety profile.

The method is used to remove cryoglobulins in several immune diseases. After plasma is initially filtrated, it is cooled to 4°C. This causes precipitation of cryoglobulins and they do not pass the second membrane. Afterwards, the cooled plasma is warmed to body temperature

Plasma Exchange in Clinical Practice http://dx.doi.org/10.5772/intechopen.76094 61

Similar to cryofiltration, plasma is firstly separated from whole blood. Before the selective filtration, the filtrate is warmed up to 40°C, causing aggregation of VLDL and LDL molecules. Then second filtration is performed and the filtrate is introduced back into patient's blood. The method is not widely used due to the fact that little is known about the changes in large

Unselective adsorption uses charcoal or ion exchange raisins to remove exogenous or endogenic toxins from blood (hemoperfusion) or from filtered plasma (plasmaperfusion). These methods are most commonly indicated in exogenous intoxications. There are reports that hemoperfusion was effective in sepsis, septic shock and disseminated intravascular coagulopathy [3]. Currently, plasmaperfusion is gaining ground over hemoperfusion due to its

In selective adsorption the initial filtrate runs through prearranged immunosorbents. Thus, specific antibodies can be selectively removed, whereas albumin and clotting factors are returned to the patient. There are two types of selective adsorption—*immunoadsorbtion (IA)* and *selective plasma adsorption*. In IA, either the plasma runs through column bearing antigens directed against certain antibodies or antibodies against certain plasma constituents. In selective plasma adsorption, plasma components are removed by binding to ligands other than

Different immunoadsorbtion (IA) techniques exist, but protein A-based IA is the most commonly used one. Protein A is a *Staphylococcus aureus*-derived molecule that binds to the Fc-region of immunoglobulin G (IgG). The principle of the procedure is similar to the previous selective methods—plasma is firstly separated from blood and then the filtrate runs through protein A—containing filters. Thus, immunoglobulins (IgG) and immune complexes are removed and the filtrate is pumped back into circulation. The method is well tolerated and is used in the following situations: acute antibody-mediated rejection, presensitized kidney transplant (KT) candidates, systemic lupus erythematosus (SLE), Guillain-Barrè syndrome, Goodpasture syndrome, myasthenia gravis, hemolytic uremic syndrome

antibodies and antigens (e.g. heparin and dextransulfate in LDL adsorption).

#### **2.2. Separation techniques**

Plasma is separated from blood cells via two major methods—centrifugal and hollow-fiber membrane separator. In addition, more selective methods were developed.

#### *2.2.1. Centrifugal separation*

The separator is a disposable rotating centrifugal bowl. Blood runs into the bowl and centrifugal force separates blood cells from plasma. Blood cells are pumped back into patient's circulation, whereas plasma is separated in sterile bags. The process can occur simultaneously or intermittently. There is no upper limit for the size of the molecules removed by centrifugal PEX. Usually the blood flow ranges between 90 and 150 ml/min. A major disadvantage of centrifugal PEX is platelet count reduction, which may reach up to 50% [1].

#### *2.2.2. Membrane PEX*

In this type of PEX, highly permeable hollow fiber membrane filters are used. The fibers have pores with diameter ranging from 0.2 to 0.5 μm. As blood runs through the fibers plasma is separated from the blood cells, which are returned in patient's circulation. All immunoglobulins are effectively cleared by this method. However, its effectiveness is poorer in immune complexes and cryoglobulins. The risk for platelet count reduction is small. Yet, there is a risk for hemolysis, especially if faster blood flow is used (normal values for the method are 90–200 ml/min). Synthetic membranes are used; plasma filters should not be reused [1].

#### *2.2.3. Selective separation techniques*

The abovementioned plasma separation techniques remove plasma from whole blood, thus causing loss of normal proteins, especially coagulation factors and albumin. In order to reduce protein loss, selective PEX techniques were introduced into practice.

#### *2.2.3.1. Double cascade PEX*

Cascade filtration is a semi-selective separation technique, in which after initial separation of plasma from blood cells, additional filtration of plasma is performed with different diameters of fiber pores, so that target protein fractions are filtered and the rest are pumped back in circulation. This technique showed up to 70% reduction in albumin loss after the procedure [2].

#### *2.2.3.2. Cryofiltration*

**2.1. Vascular access**

60 Plasma Medicine - Concepts and Clinical Applications

**2.2. Separation techniques**

*2.2.1. Centrifugal separation*

*2.2.2. Membrane PEX*

*2.2.3. Selective separation techniques*

*2.2.3.1. Double cascade PEX*

In most of the cases, central venous catheters are used in PEX, especially in acute conditions. They can be placed in internal jugular, femoral and subclavian veins. However, if life-long treatment is needed (e.g., LDL apheresis), arteriovenous fistula creation may be required. In addition, as the blood flow is low (90–150 ml/min), large peripheral veins can be used (cubital veins). Single-vein access is also possible but in cases where centrifugal separation of plasma is used.

Plasma is separated from blood cells via two major methods—centrifugal and hollow-fiber

The separator is a disposable rotating centrifugal bowl. Blood runs into the bowl and centrifugal force separates blood cells from plasma. Blood cells are pumped back into patient's circulation, whereas plasma is separated in sterile bags. The process can occur simultaneously or intermittently. There is no upper limit for the size of the molecules removed by centrifugal PEX. Usually the blood flow ranges between 90 and 150 ml/min. A major disadvantage of

In this type of PEX, highly permeable hollow fiber membrane filters are used. The fibers have pores with diameter ranging from 0.2 to 0.5 μm. As blood runs through the fibers plasma is separated from the blood cells, which are returned in patient's circulation. All immunoglobulins are effectively cleared by this method. However, its effectiveness is poorer in immune complexes and cryoglobulins. The risk for platelet count reduction is small. Yet, there is a risk for hemolysis, especially if faster blood flow is used (normal values for the method are 90–200 ml/min). Synthetic membranes are used; plasma filters should not be reused [1].

The abovementioned plasma separation techniques remove plasma from whole blood, thus causing loss of normal proteins, especially coagulation factors and albumin. In order to reduce

Cascade filtration is a semi-selective separation technique, in which after initial separation of plasma from blood cells, additional filtration of plasma is performed with different diameters of fiber pores, so that target protein fractions are filtered and the rest are pumped back in circulation. This technique showed up to 70% reduction in albumin loss after the procedure [2].

membrane separator. In addition, more selective methods were developed.

centrifugal PEX is platelet count reduction, which may reach up to 50% [1].

protein loss, selective PEX techniques were introduced into practice.

The method is used to remove cryoglobulins in several immune diseases. After plasma is initially filtrated, it is cooled to 4°C. This causes precipitation of cryoglobulins and they do not pass the second membrane. Afterwards, the cooled plasma is warmed to body temperature again and is returned to the patient.

#### *2.2.3.3. Thermofiltration*

Similar to cryofiltration, plasma is firstly separated from whole blood. Before the selective filtration, the filtrate is warmed up to 40°C, causing aggregation of VLDL and LDL molecules. Then second filtration is performed and the filtrate is introduced back into patient's blood. The method is not widely used due to the fact that little is known about the changes in large molecules after being exposed to higher temperatures [2].

#### *2.2.3.4. Unselective adsorption*

Unselective adsorption uses charcoal or ion exchange raisins to remove exogenous or endogenic toxins from blood (hemoperfusion) or from filtered plasma (plasmaperfusion). These methods are most commonly indicated in exogenous intoxications. There are reports that hemoperfusion was effective in sepsis, septic shock and disseminated intravascular coagulopathy [3]. Currently, plasmaperfusion is gaining ground over hemoperfusion due to its improved effectiveness and improved safety profile.

#### *2.2.3.5. Selective adsorption*

In selective adsorption the initial filtrate runs through prearranged immunosorbents. Thus, specific antibodies can be selectively removed, whereas albumin and clotting factors are returned to the patient. There are two types of selective adsorption—*immunoadsorbtion (IA)* and *selective plasma adsorption*. In IA, either the plasma runs through column bearing antigens directed against certain antibodies or antibodies against certain plasma constituents. In selective plasma adsorption, plasma components are removed by binding to ligands other than antibodies and antigens (e.g. heparin and dextransulfate in LDL adsorption).

Different immunoadsorbtion (IA) techniques exist, but protein A-based IA is the most commonly used one. Protein A is a *Staphylococcus aureus*-derived molecule that binds to the Fc-region of immunoglobulin G (IgG). The principle of the procedure is similar to the previous selective methods—plasma is firstly separated from blood and then the filtrate runs through protein A—containing filters. Thus, immunoglobulins (IgG) and immune complexes are removed and the filtrate is pumped back into circulation. The method is well tolerated and is used in the following situations: acute antibody-mediated rejection, presensitized kidney transplant (KT) candidates, systemic lupus erythematosus (SLE), Guillain-Barrè syndrome, Goodpasture syndrome, myasthenia gravis, hemolytic uremic syndrome (HUS) and so on.

Other adsorbents can carry antibodies against proteins to be removed too. Polyvinyl-alcohol gel, bound to tryptophan, is used for removal of anti-acetylcholine-receptor antibodies in myasthenia gravis; phenylalanine-bound polyvinyl-alcohol gel for selective removal of anti-DNA antibodies; and cardiolipin antibodies in SLE [2].

An easier way to assess the needed PEX volume is 30–50 ml/kg body weight.

PEX is usually performed daily or every other day. The duration of treatment is 10–14 procedures, but it can be guided by clinical outcomes and laboratory results (auto-antibody titers,

PEX and IA have beneficial effects on different diseases due to the following mechanisms [2]:

• Elimination of pathological constituents—alloantibodies/autoantibodies, paraproteins,

• Substitution of plasma proteins: clotting factors, hormone carrier proteins, immunoglobu-

• Modifying immune cells' functions: deblocking of reticuloendothelial system and modify-

Despite the mentioned beneficial effects, PEX is not effective in immune disease when used alone, as it influences pre-existing pathological molecules and has no influence on their formation. It was established that the procedure causes rapid decrease in antibody titers, which is followed by increased antibody production and B-cell proliferation [6]. In addition, the combination PEX and immunosuppressive therapy has better results compared to using

Several combinations have been suggested. Initially, steroids of 1–2 mg/kg for 2–3 weeks or cyclophosphamide of 2–3 mg/kg for 2–3 weeks, followed by azathioprine of 1–2 mg/kg for several months after cyclophosphamide treatment, were suggested. Later, cyclophosphamide pulses and PEX were found superior to oral intake and PEX [7]. Over the last years new immunosuppressive agents have been introduced as concomitant therapy in PEX—cyclosporine A, tacrolimus and mycophenolic acid [8]. In addition, biological agents are more widely used—monoclonal antibodies (e.g., rituximab) and intravenous immunoglobulin (IVIG).

Calcium gluconate and potassium chloride can be infused to counterbalance PEX-associated

/weekly, for 2–4 weeks. IVIG is applied, 100 mg/kg,

Plasma Exchange in Clinical Practice http://dx.doi.org/10.5772/intechopen.76094 63

*2.5.2. Frequency of PEX*

platelet count, etc).

lins and so on.

**2.6. PEX: mechanism of action**

ing lymphocyte response.

*2.6.1. Immunosuppressive treatment in PEX*

Rituximab is usually applied, 375 mg/m2

after each PEX [9, 10].

*2.6.2. Additional medications*

hypocalcaemia and hypokalemia.

plasma exchange and immunosuppression alone.

circulating immune complexes, toxins and so on.

#### **2.3. Anticoagulation**

Practically in all PEX procedures, anticoagulation is needed. In centrifugal PEX, usually citrate anticoagulation is used, whereas in membrane PEX, heparin is the anticoagulant of choice [1]. Citrate has advantages in patients with high bleeding risk, as it has no influence on systemic coagulation, but it is associated with increased incidence of hypocalcaemia. The usual dose of heparin is bolus dose 2000–5000 IU, followed by infusion of 500–2000 IU per hour. Anticoagulants are administered pre-filter. Low-molecular weight heparins (LMWH) can be used too. They are associated with lower incidence of side effects and more selective prevention of clotting. In our institution low-molecular weight heparins are used in doses, 0.01 ml/kg body weight or generally 0.8–1.0 ml LMWH per procedure.

#### **2.4. Substitution fluids**

PEX requires large volumes of replacement fluids. A single procedure was found to reduce plasma macromolecule levels by 60% [4]. The use of crystalloids is ineffective, as they are not capable of preserving the intravascular oncotic pressure. Gelatin-based plasma expanders have limited practical importance, as they have shorter half life compared to albumin-based fluids. Therefore, the most widely used substitution fluid is human albumin. Replacement volume reaches 50 ml/kg, 4–5% human albumin per procedure. The major disadvantage of albumin replacement is the lack of coagulation factors. Therefore fresh frozen plasma (FFP) can be applied after PEX. In certain diseases, the replacement fluid should consist of FFP only— for example, HUS, thrombotic thrombocytopenia purpura (TTP) and so on. Other indications for FFP use are reduction of plasma fibrinogen level below 1.25 g/l, increase of prothrombin time more than 2 s above normal values and increased risk of bleeding (pulmonary hemorrhage, 48 h after biopsy/surgery) [1]. FFP should be used with caution, as its application is associated with hypotension, citrate-associated paraesthesia, urticaria, anaphylaxis and blood-borne infections.

#### **2.5. Treatment volume: frequency of PEX**

#### *2.5.1. Treatment volume*

A formula for determining the needed volume of single PEX was suggested by A.A. Kaplan [5]:

$$\text{Volume PEX} = \left[0.065 \* body \,\,\text{weight(kg)}\right] \* (1 - Hct) \tag{1}$$

where *kg: kilograms and Hct: hematocrit*.

An easier way to assess the needed PEX volume is 30–50 ml/kg body weight.

#### *2.5.2. Frequency of PEX*

Other adsorbents can carry antibodies against proteins to be removed too. Polyvinyl-alcohol gel, bound to tryptophan, is used for removal of anti-acetylcholine-receptor antibodies in myasthenia gravis; phenylalanine-bound polyvinyl-alcohol gel for selective removal of anti-

Practically in all PEX procedures, anticoagulation is needed. In centrifugal PEX, usually citrate anticoagulation is used, whereas in membrane PEX, heparin is the anticoagulant of choice [1]. Citrate has advantages in patients with high bleeding risk, as it has no influence on systemic coagulation, but it is associated with increased incidence of hypocalcaemia. The usual dose of heparin is bolus dose 2000–5000 IU, followed by infusion of 500–2000 IU per hour. Anticoagulants are administered pre-filter. Low-molecular weight heparins (LMWH) can be used too. They are associated with lower incidence of side effects and more selective prevention of clotting. In our institution low-molecular weight heparins are used in doses,

PEX requires large volumes of replacement fluids. A single procedure was found to reduce plasma macromolecule levels by 60% [4]. The use of crystalloids is ineffective, as they are not capable of preserving the intravascular oncotic pressure. Gelatin-based plasma expanders have limited practical importance, as they have shorter half life compared to albumin-based fluids. Therefore, the most widely used substitution fluid is human albumin. Replacement volume reaches 50 ml/kg, 4–5% human albumin per procedure. The major disadvantage of albumin replacement is the lack of coagulation factors. Therefore fresh frozen plasma (FFP) can be applied after PEX. In certain diseases, the replacement fluid should consist of FFP only— for example, HUS, thrombotic thrombocytopenia purpura (TTP) and so on. Other indications for FFP use are reduction of plasma fibrinogen level below 1.25 g/l, increase of prothrombin time more than 2 s above normal values and increased risk of bleeding (pulmonary hemorrhage, 48 h after biopsy/surgery) [1]. FFP should be used with caution, as its application is associated with hypotension, citrate-associated paraesthesia, urticaria, anaphylaxis

A formula for determining the needed volume of single PEX was suggested by A.A. Kaplan [5]:

*Volume PEX* = [0.065 ∗ *body weight*(*kg*)] ∗ (1 − *Hct*) (1)

DNA antibodies; and cardiolipin antibodies in SLE [2].

62 Plasma Medicine - Concepts and Clinical Applications

0.01 ml/kg body weight or generally 0.8–1.0 ml LMWH per procedure.

**2.3. Anticoagulation**

**2.4. Substitution fluids**

and blood-borne infections.

*2.5.1. Treatment volume*

**2.5. Treatment volume: frequency of PEX**

where *kg: kilograms and Hct: hematocrit*.

PEX is usually performed daily or every other day. The duration of treatment is 10–14 procedures, but it can be guided by clinical outcomes and laboratory results (auto-antibody titers, platelet count, etc).

#### **2.6. PEX: mechanism of action**

PEX and IA have beneficial effects on different diseases due to the following mechanisms [2]:


#### *2.6.1. Immunosuppressive treatment in PEX*

Despite the mentioned beneficial effects, PEX is not effective in immune disease when used alone, as it influences pre-existing pathological molecules and has no influence on their formation. It was established that the procedure causes rapid decrease in antibody titers, which is followed by increased antibody production and B-cell proliferation [6]. In addition, the combination PEX and immunosuppressive therapy has better results compared to using plasma exchange and immunosuppression alone.

Several combinations have been suggested. Initially, steroids of 1–2 mg/kg for 2–3 weeks or cyclophosphamide of 2–3 mg/kg for 2–3 weeks, followed by azathioprine of 1–2 mg/kg for several months after cyclophosphamide treatment, were suggested. Later, cyclophosphamide pulses and PEX were found superior to oral intake and PEX [7]. Over the last years new immunosuppressive agents have been introduced as concomitant therapy in PEX—cyclosporine A, tacrolimus and mycophenolic acid [8]. In addition, biological agents are more widely used—monoclonal antibodies (e.g., rituximab) and intravenous immunoglobulin (IVIG). Rituximab is usually applied, 375 mg/m2 /weekly, for 2–4 weeks. IVIG is applied, 100 mg/kg, after each PEX [9, 10].

#### *2.6.2. Additional medications*

Calcium gluconate and potassium chloride can be infused to counterbalance PEX-associated hypocalcaemia and hypokalemia.
