Apheresis & Extracorporeal Circulation

Apheresis and Extracorporeal Circulation (ECC) are fascinating areas where we interact with blood outside the body for specific therapeutic or collection purposes. They represent advanced applications within transfusion medicine and critical care

Think of Extracorporeal Circulation as the broad umbrella term for any procedure where blood is taken out of the body, circulated through a device for some purpose, and then returned to the patient. Apheresis is a specific type of ECC focused on separating and selectively removing or collecting certain blood components

Apheresis: Selective Separation and Collection/Removal

Apheresis (from the Greek word meaning “to take away” or “to separate”) involves withdrawing whole blood from an individual (donor or patient), passing it through a medical device (apheresis machine) that separates it into components, collecting the desired component(s) or removing the undesired one(s), and returning the remaining elements to the individual

Basic Principle Most apheresis machines use centrifugation to separate blood components based on differences in their density (RBCs are heaviest, then WBCs, then platelets, then plasma is lightest). Some specialized procedures might use filtration based on size

Why Use Apheresis?

1. Component Collection (Donation) To obtain a larger quantity or purer concentration of a specific blood component from a single, healthy donor
2. Therapeutic Apheresis (Patient Treatment) To remove a harmful substance or cellular element from a patient’s blood to treat a specific disease

Apheresis for Component Collection (Donors)

• Plateletpheresis: Collects a large dose of platelets (equivalent to 4-6 whole blood-derived units) from a single donor. This is the preferred source for platelet transfusions, reducing recipient exposure to multiple donors
• Plasmapheresis: Collects plasma. Used for obtaining Source Plasma (further manufactured into derivatives like albumin, IVIG, coagulation factors) or for collecting specific types like Convalescent Plasma or ABO-compatible plasma for transfusion
• Erythrocytapheresis (Red Cell Apheresis): Collects two units of RBCs (“double reds”) from a single qualifying donor. More efficient RBC collection
• Leukapheresis: Collects leukocytes, primarily granulocytes (Granulocytapheresis). Used infrequently to provide granulocyte transfusions for severely neutropenic patients with specific infections unresponsive to antibiotics. Requires donor stimulation (G-CSF, steroids)
• Hematopoietic Progenitor Cell (HPC) Collection (Stem Cell Collection): Collects peripheral blood stem cells (PBSCs) after the donor has been mobilized (usually with G-CSF) to release stem cells from the bone marrow into the circulation. Used for stem cell transplantation

Therapeutic Apheresis (Patients)

• Plasma Exchange (PEX) / Therapeutic Plasmapheresis (TPE)
  • Goal: Remove harmful substances circulating in the patient’s plasma (e.g., autoantibodies, immune complexes, toxins, abnormal proteins)
  • Procedure: Patient’s plasma is separated and removed; replacement fluid (usually Albumin 5%, sometimes FFP if coagulation factors are also needed, or a combination) is returned with the patient’s own cells
  • Indications: Thrombotic Thrombocytopenic Purpura (TTP - life-saving!), Guillain-Barré Syndrome, Myasthenia Gravis crisis, Hyperviscosity Syndrome (e.g., Waldenström’s), certain autoimmune or neurologic disorders
• Cytapheresis (Selective Cell Removal)
  • Red Cell Exchange: Remove a large volume of the patient’s abnormal RBCs and replace them with donor RBCs
    • Indications: Sickle Cell Disease (acute stroke prevention/treatment, acute chest syndrome, preoperative preparation), severe Babesiosis or Malaria infections
  • Leukocytapheresis (Therapeutic): Remove excessively high numbers of abnormal white blood cells (leukocytes)
    • Indications: Hyperleukocytosis in Acute Myeloid Leukemia (AML) to prevent leukostasis (sludging of blasts in small vessels)
  • Thrombocytapheresis (Therapeutic): Remove excessively high numbers of platelets
    • Indications: Symptomatic extreme thrombocytosis (e.g., Essential Thrombocythemia) to reduce risk of thrombosis or bleeding
• Extracorporeal Photopheresis (ECP)
  • Goal: Treat certain T-cell mediated disorders
  • Procedure: Leukocytes (primarily lymphocytes) are collected via apheresis, treated ex vivo with a photosensitizing agent (8-methoxypsoralen), exposed to UVA light, and then returned to the patient. This induces apoptosis (cell death) in the treated T-cells and modulates the immune response
  • Indications: Cutaneous T-Cell Lymphoma (CTCL), Graft-versus-Host Disease (GVHD) prophylaxis/treatment after stem cell transplant, some autoimmune disorders, organ transplant rejection
• LDL Apheresis
  • Goal: Remove Low-Density Lipoprotein (LDL) cholesterol
  • Procedure: Uses specific adsorption columns or filtration to remove LDL from plasma
  • Indications: Severe Familial Hypercholesterolemia unresponsive to medication

Key Considerations in Apheresis

• Anticoagulation: Citrate is typically used; monitoring for and managing citrate toxicity (hypocalcemia) is essential
• Vascular Access: Requires good venous access (often large-bore peripheral IVs or central venous catheter)
• Fluid Shifts: Especially important in therapeutic procedures; careful monitoring of fluid balance is needed
• Cell Counts: Monitoring counts pre- and post-procedure
• Donor Reactions: Vasovagal reactions, citrate toxicity symptoms

Extracorporeal Circulation (ECC): Beyond Apheresis

ECC refers to any procedure where blood circulates outside the body through a machine. Therapeutic apheresis is a form of ECC, but ECC also includes other critical care techniques:

• Cardiopulmonary Bypass (CPB): The “heart-lung machine” used during open-heart surgery. Takes over the function of both the heart (pumping) and the lungs (oxygenation/CO2 removal) allowing the surgeon to operate on a still, bloodless heart. Requires systemic anticoagulation (heparin), hemodilution (priming the circuit), and often significant blood product support
• Extracorporeal Membrane Oxygenation (ECMO): Provides prolonged cardiac and/or respiratory support when the heart and/or lungs are failing severely. Blood is drained, oxygenated by an artificial lung, CO2 removed, and returned. Can be Veno-Venous (VV-ECMO, lung support only) or Veno-Arterial (VA-ECMO, heart and lung support). Also requires anticoagulation and careful hematologic management
• Hemodialysis: Used for patients with kidney failure. Blood circulates through a dialyzer (artificial kidney) where waste products and excess fluid are removed via diffusion and ultrafiltration across a semipermeable membrane
• Continuous Renal Replacement Therapy (CRRT): A slower, continuous form of dialysis used for critically ill patients with acute kidney injury who may not tolerate conventional hemodialysis

Common Challenges of ECC Circuits (Relevant to Transfusion Practice)

• Hemodilution: The circuit is often primed with crystalloid solution, diluting the patient’s blood components (RBCs, platelets, factors)
• Coagulation Activation/Consumption: Contact of blood with artificial surfaces activates platelets and the coagulation cascade, necessitating anticoagulation (usually heparin) but also leading to potential consumption of factors and platelets (DIC-like picture)
• Hemolysis: Mechanical shear stress from pumps and tubing can damage RBCs
• Inflammatory Response: Contact with artificial surfaces triggers a systemic inflammatory response
• Temperature Changes: Blood cools as it passes through the circuit; warming is often necessary

Key Terms

• Apheresis: Procedure separating whole blood into components ex vivo, collecting desired components (donation) or removing harmful ones (therapeutic)
• Extracorporeal Circulation (ECC): Any procedure where blood circulates outside the body through a device for therapeutic purposes
• Plasmapheresis / Plasma Exchange (PEX/TPE): Apheresis procedure removing patient plasma and replacing it with fluid (albumin/FFP) to eliminate harmful plasma constituents
• Cytapheresis: Apheresis procedure removing specific cellular components (RBCs, WBCs, platelets)
• Red Cell Exchange: Cytapheresis removing patient RBCs and replacing them with donor RBCs (common in Sickle Cell Disease)
• Extracorporeal Photopheresis (ECP): Apheresis procedure where collected leukocytes are treated with a photosensitizer and UVA light before reinfusion to modulate immune responses
• Cardiopulmonary Bypass (CPB): ECC circuit taking over heart and lung function during cardiac surgery
• ECMO (Extracorporeal Membrane Oxygenation): ECC circuit providing prolonged cardiac and/or respiratory support
• Hemodialysis: ECC procedure filtering waste products from blood for patients with kidney failure
• Citrate Toxicity: Hypocalcemia resulting from the anticoagulant citrate binding ionized calcium, a risk during apheresis
• Leukostasis: Sludging of excessive white blood cells in small blood vessels, a complication of hyperleukocytosis sometimes treated with leukocytapheresis