Apheresis is a procedure which involves the process of connecting an individual (donor or patient) with an apparatus (cell separator/ apheresis machine) which separates one specific component of blood and returns the remaining back to the individual. The apheresis procedure is a challenging scenario when being done in a pediatric patient. This is due to various issues specific to this age group such as the developing or growing nature of their body, small blood volume, attaining vascular access, use of anticoagulation and identifying and managing adverse events during the procedure. Before planning any apheresis procedure, it is recommended that the apheresis procedure is done by a trained apheresis physician or paramedical staff. The apheresis procedure involves knowing your patients (healthy or disease state), indication of performing the apheresis procedure and knowing the cell separator (apheresis machine). It is recommended that the apheresis procedure should be done with a pediatric physician's support and under continuous close monitoring of the hemodynamic status of the child.
- The apheresis procedure can be broadly divided into cytapheresis (removing a specific component of blood) or exchange (removing a specific component of blood and replacing it with a compatible blood component/ product)
- Cytapheresis (collection or removal): This process of apheresis may include the removal of one part of blood such as peripheral blood hematopoietic stem cells or leukocytes (in hyper-leukocytosis) or platelets (in hyper-thrombocytosis).
- Exchange: This is a process of exchanging one part of blood such as plasma (therapeutic plasma exchange) or RBC (therapeutic red cell exchange) and replacing it with a compatible replacement fluid.
- Children are not small adults and apheresis machines are developed for adult patients and require very specific customization to perform procedures in pediatrics.
- The apheresis team needs to understand that there is a significant difference in the total blood volume, tissue blood flow rates, tissue blood volume, extra Corporeal volume and cardiac output between adults and a growing child.
- There is a significant difference in hemostasis among adults and children regarding procoagulant factor level, anticoagulant level, platelet function and ability to respond to any injury.
- The apheresis machines are built to support procedures in adult individuals. One of the major limitations of performing an apheresis procedure in pediatrics is the small total blood volume.
- The blood volume of infants of less than 3 months can range from 80-100 ml/kg whereas for children more than 3 months may range from 65-75 ml/kg. The blood volume in an adolescent is around 70 ml/kg (as in an adult).
- Extra Corporeal Volume (ECV) in an apheresis kit is the amount of blood which stays in the tubing of the kit during the apheresis procedure. This is the major limiting factor to be assessed when planning an apheresis procedure in the pediatric age group of patients.
- Extra Corporeal Volume (ECV) can be calculated as the percentage of the total blood volume (TBV). [(ECV/TBV) x 100=ECV (%)]
- Extra Corporeal Red Cell Volume (ERCV) is the percentage of total red cell volume (RCV) in the tubing set. [(ERCV/RCV) x 100=ERCV (%)]
- Intra-procedure Hematocrit: [(Initial RCV-ERCV/TBV) x 100= Intra Procedural Hematocrit (%)]
- Extra Corporeal Volume (ECV) is known for every kit (machine) and is fixed. ECV is low for continuous flow apheresis machines as compared to intermittent flow machines. The ratio of ECV to TBV can directly predict the net volume shift that the patient may have during the procedure.
- ECV can be a critical factor and represent a larger fraction of TBV if the weight of the child is less than 25 kg, TBV <1000 ml, Hematocrit < 20%, and hemoglobin <8 gm/dl.
- The aim is to keep the ECV <10-15% of the TBV in the case of the pediatric group of patients as higher ECV can lead to hypovolemia.
- Priming the kit: Priming the apheresis kit is one of the most accepted ways to manage the issue of net blood volume shift during the procedure. The priming of the kit with a compatible packed red blood cell unit (irradiated in case of PBSC harvest) is recommended to avoid a drop in blood volume and RBC in pediatric patients. The priming of the kit is indicated when the following
- If ECV is >15% of the TBV of the patient
- The body weight of the patient is less than 25 kg
- Hematocrit of the patient is less than 20% (even when the ECV is < 15% of TBV)
- Rinse back is a process of pushing the remaining blood in the kit back into the patient. The decision to rinse back should be carefully made in case of pediatric apheresis. The rinse back can create more positive fluid balance in the patient and may result in hypertension and/or fluid overload. The rinse back may be considered if the patient had a low hematocrit at the beginning of the procedure.
- The apheresis procedure requires adequate venous access to maintain and sustain high blood flow rates.
- In adults, one or two large bore needles (16-18G) usually are adequate to support the flow rates.
- In younger children, it may not be possible to gain access by the peripheral insertion of 16G or 18G needles. Central venous lines often become the major source of venous access to pediatric patients.
- Central catheters should be rigid double-lumen non-collapsable under negative pressure applied by the apheresis machine and sustain a flow rate of 20-40 ml/min. Following body size and weight may dictate the length and French size of the dual-lumen central venous catheters:
- Weight < 3kg: Consider two single-lumen (5 Fr.)
- Weight 3-10kg: 7 Fr. double-lumen
- Weight 10-20kg: 8 or 9 Fr. double-lumen
- Weight 20-50kg: 9 or 10 Fr. double-lumen
- Weight >50kg: 11.5 or 12 or 13 Fr. double-lumen
- In the emergency setting, a double-lumen central venous catheter at the femoral site may be preferred. However, for an outpatient setting an internal jugular/ subclavian CVC may be preferred.
- Anticoagulation is being offered with the apheresis procedure to prevent coagulation in the extracorporeal circuit i.e. to maintain the blood in a liquid state in the kit.
- ACD-A is the most common citrate-based anticoagulant is used in the apheresis kits. Heparin can also be used with ACD-A in some specific indications.
- Citrate from ACD-A causes the reduction of ionised calcium in the patients. This reduction of ionised calcium in patients can lead to various citrate-based toxicities, from mild paresthesia to severe side effects such as dysarthrias and seizures.
- The reduction of ionised calcium can be managed by calcium replacement.
- Any procedure can be very stressful for any child and the family.
- Calm and cooperative child-parent increase the likelihood of a successful procedure
- The following things can be attempted
- Bringing familiar toys, favourite foods, a sibling or a friend
- Activities appropriate for the child's age
- Use of distraction can be used
- Parental/ family involvement can be helpful in reducing the anxiety both for the parent and the child
- One should teach the child to inform if they feel anything funny or different during the procedure.
- If required a mild sedation can also be used under the active supervision of a pediatrician.
- When considering apheresis procedures in pediatric patients, obtaining informed consent from the legal guardians is crucial, ensuring they understand the purpose, risks, benefits, and alternatives of the procedure.
- Additionally, assent from the child, when developmentally appropriate, is equally important. This involves explaining the procedure in an age-appropriate way, acknowledging the child's perspectives, and involving them in the decision-making process. Respecting both the guardians' consent and the child's assent fosters trust, supports ethical care, and encourages a positive experience during apheresis.
