Plasmapheresis
Steps in therapeutic plasma exchange
The following is an example of the steps involved in performing therapeutic plasma exchange using centrifugation-based equipment such as the Spectra Auto PBSC:
-
Any heparin that may be present in each of the two lumina of a central venous catheter is removed
-
A waste of 3 mL is then discarded
-
Laboratory studies, including complete blood count (CBC), calcium, and fibrinogen, are ordered and specimens sent from the draw lumen
-
A flush with 10 mL of normal saline is placed in the draw lumen
-
The draw and return lumina are then connected to the tubing, which is previously primed with normal saline; however, if a patient weighs less than 20 kg, then the draw and return tubing are primed with packed red blood cells (RBCs) instead of normal saline
-
Height and weight are then entered into the system to allow estimation of total blood volume (TBV)
-
Plasma volume is then calculated as follows: TBV × (1 – hematocrit)
-
A replacement product is chosen
-
The total volume of the desired replacement product is entered—usually either 1 plasma volume (40 mL/kg) or 1.5 plasma volume (60 mL/kg)
-
A centrifuge speed is determined by the software on the basis of the data entered
-
The device then draws whole blood through the draw lumen to the centrifuge
-
Plasma is separated by the centrifuge and collected for discard
-
RBCs are also separated by the centrifuge, then returned to the patient along with the previously selected colloid of either albumin or fresh frozen plasma (FFP)
-
After the desired amount of plasma is removed, the machine is disconnected from the patient, and heparin is instilled into each catheter lumen to prevent clotting until the lumen is accessed again
-
A post–plasma exchange fibrinogen level is checked if albumin was used as the replacement product (albumin does not contain fibrinogen, as opposed to FFP) to assess whether the patient has become severely hypofibrinogenemic
Replacement products
Options for replacement fluid during plasma exchange include albumin, electrolyte solutions, hydroxyethyl starch, FFP, and purified protein products such as individual clotting factors or antithrombin III. [18] Deciding which replacement product to use is based on the underlying condition and the risks and benefits associated with each replacement product. In general, albumin is the most common replacement product because of its low side-effect profile and broad availability. [18]
Symptomatic adjustments
If signs of hypocalcemia are present, replacement calcium can be administered either intravenously (IV) or orally. Additionally, the whole blood–to–citrate ratio can be titrated to minimize hypocalcemic symptoms, which are usually related to the amount of citrate being used as an anticoagulant. [19]
If signs of hypomagnesemia are present, replacement magnesium can be administered IV.
If signs of general discomfort are present, the return rate can be adjusted downward.
If signs of hypotension are present, normal saline boluses can be administered.
If signs of a transfusion reaction are present, the product infusion is discontinued, and diphenhydramine and hydrocortisone are given. In cases of anaphylaxis or respiratory distress, epinephrine can be administered as well.
Special considerations in pediatric patients
Magnesium is not always given prophylactically, though the decision is physician-dependent. [20]
If a patient weighs less than 20 kg, the draw and return tubing are primed with packed RBCs instead of normal saline.
Return rates of blood product are on the order of 1.5 mL/kg/min, as opposed to the standard 70 mL/min flat rate used in adults. [21]
Complications
Patients may experience symptoms of hypocalcemia and or hypomagnesemia during and after the procedure, which can be treated with replacement calcium and magnesium, respectively. [22]
Patients frequently become hypothermic during the procedure, in which case they should be warmed appropriately.
Patients can experience transfusion-related reactions, in particular with FFP, and should be treated with diphenhydramine, hydrocortisone, and/or epinephrine, depending on the severity of the reaction. These reactions can occur during and after the transfusion.
Patients can experience hypotension as a result of rapid fluid shifts, and proper precautions should be taken to minimize complications such as unintended falls.
Patients can become thrombocytopenic and hypofibrinogenemic after plasmapheresis (especially if albumin is being used as a replacement product) and should be monitored for signs of bleeding.
Patients may also be at further risk for developing hypotension if they have a history of taking angiotensin-converting enzyme (ACE) inhibitors, in particular while undergoing column-based plasmapheresis. [23] The suspected mechanism is related to increased bradykinin levels caused by use of ACE inhibitors. This accumulation of kinins leads to hypotension, flushing, and gastrointestinal symptoms. Patients are therefore advised to stop all ACE inhibitors at least 24 hours before starting plasmapheresis.
