Apheresis and extracorporeal circulation

6 ASCP MLS practice questions on Apheresis and extracorporeal circulation, part of Blood Banking. The first 6 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

1. Question 1 · Easy

   Therapeutic plasma exchange mainly works by:

   1. ARemoving harmful substances such as autoantibodies
   2. BAdding donor white cells to fight infection
   3. CRemoving excess platelets from the blood
   4. DReplacing the patient's red cells with donor cells

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   Answer: A · Removing harmful substances such as autoantibodies

   The patient's plasma is removed and replaced with albumin or plasma, taking out autoantibodies, immune complexes or toxins. Conditions such as Guillain-Barré syndrome, myasthenic crisis and TTP respond well. Several procedures are usually needed, because antibodies outside the blood vessels move back into the plasma. Red cell exchange and plateletpheresis are separate procedures.

   • B: Granulocyte collection gives donor white cells; plasma exchange does not.
   • C: Removing platelets is therapeutic plateletpheresis.
   • D: Replacing red cells is red cell exchange.

2. Question 2 · Hard

   A patient with sickle cell disease has an acute ischemic stroke. Hemoglobin is 8.5 g/dL (85 g/L) and HbS is 85%. The most appropriate transfusion approach is:

   1. APlasma exchange with 5% albumin
   2. BAutomated red cell exchange to HbS below 30%
   3. CPlatelet transfusion to improve clotting
   4. DSimple transfusion to a hemoglobin of 13 g/dL

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   Answer: B · Automated red cell exchange to HbS below 30%

   Red cell exchange quickly lowers the share of sickle hemoglobin without raising the hemoglobin too far. The usual target is HbS below 30% with a hemoglobin of about 10 g/dL (100 g/L). Simple transfusion to a high hemoglobin increases blood viscosity and can worsen ischemia. The red cells are HbS-negative and matched at least for C, E and K.

   • A: Plasma exchange does not remove sickle red cells.
   • C: Stroke in sickle cell disease is caused by sickling, not a bleeding problem.
   • D: A hemoglobin of 13 g/dL in sickle cell disease raises viscosity and stroke risk.

3. Question 3 · Hard

   A 70 kg patient with a hematocrit of 40% needs a 1.5 plasma-volume exchange. Using a blood volume of 70 mL/kg, about how much plasma is exchanged?

   1. A2,940 mL
   2. B5,880 mL
   3. C4,410 mL
   4. D7,350 mL

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   Answer: C · 4,410 mL

   Blood volume = 70 × 70 = 4,900 mL. Plasma volume = 4,900 × (1 − 0.40) = 2,940 mL. A 1.5 plasma-volume exchange = 1.5 × 2,940 = 4,410 mL. Apheresis instruments do this calculation from height, weight and hematocrit, but the operator should check it.

   • A: 2,940 mL is one plasma volume, not 1.5.
   • B: 5,880 mL is two plasma volumes.
   • D: 7,350 mL uses the blood volume instead of the plasma volume.

4. Question 4 · Medium

   A single plasma-volume exchange removes about what share of a substance that stays within the plasma, such as IgM?

   1. AAbout 86%
   2. BAbout 63%
   3. CAbout 50%
   4. DAbout 100%

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   Answer: B · About 63%

   Removed plasma is continuously replaced, so the replacement fluid mixes with the remaining plasma and removal follows an exponential curve. One plasma volume removes about 63%, 1.5 volumes about 78% and 2 volumes about 86%. IgM stays mostly in the blood vessels, so it is removed well. IgG is largely outside the vessels and moves back, so repeated exchanges are needed.

   • A: 86% is the removal after about two plasma volumes.
   • C: 50% underestimates the removal achieved by one plasma volume.
   • D: Some of the substance is always left, because replacement fluid mixes with the plasma.

5. Question 5 · Medium

   Which condition needs plasma, rather than albumin, as the replacement fluid in therapeutic plasma exchange?

   1. AMyasthenic crisis
   2. BChronic inflammatory demyelinating polyneuropathy
   3. CGuillain-Barré syndrome
   4. DThrombotic thrombocytopenic purpura

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   Answer: D · Thrombotic thrombocytopenic purpura

   TTP is caused by a lack of the ADAMTS13 enzyme, usually from an autoantibody. Plasma exchange removes the antibody and replaces the missing ADAMTS13, which albumin cannot supply. For most neurologic indications, only removal matters, so 5% albumin is used and avoids plasma reactions. Repeated albumin-only exchanges can lower clotting factors, which are checked between procedures.

   • A: Myasthenic crisis needs only antibody removal, so albumin is standard.
   • B: This neuropathy needs only antibody removal, so albumin is standard.
   • C: Guillain-Barré syndrome needs only antibody removal, so albumin is standard.

6. Question 6 · Hard

   A 67-year-old man has heavy chest-tube bleeding 1 hour after coronary artery bypass grafting on cardiopulmonary bypass. His heparin was reversed with protamine at the end of bypass. Results: hemoglobin 9.8 g/dL (98 g/L), platelets 128 x 10^3/µL, fibrinogen 240 mg/dL (2.4 g/L), aPTT 58 s (reference 25-35 s). Kaolin TEG: R time 16 min (reference 5-10 min), alpha angle and maximum amplitude normal, LY30 1% (reference below 8%). Heparinase TEG: R time 7 min. The most appropriate treatment is:

   1. AMore protamine sulfate
   2. BPlasma at 15 mL/kg
   3. COne apheresis platelet unit
   4. DTranexamic acid infusion

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