Large volume leukapheresis with the Cobe Spectra AutoPBSC in a 7-kg child.

To the Editor: Peripheral blood stem cell (PBSC) collection in small children is limited by several factors including high extracorporeal volume, vascular access and line placement, patient tolerance, and citrate toxicity. We report our experience in PBSC collection using large volume leukapheresis (LVL), that is, processing more than 3 blood volumes, with the Cobe Spectra AutoPBSC procedure in a 7 kg and 5-month-old infant. The patient had been diagnosed of congenital acute myeloid leukemia (M5a, FAB) in August 2004. He achieved complete remission after 2 cycles of induction chemotherapy with idarubicin, cytarabine, and etoposide and received afterward 2 consolidation cycles with mitoxantrone and high-dose cytarabine. The patient had no brothers so an autologous PBSC transplant in first complete remission was planned. The patient was mobilized with granulocyte colony-stimulating factor at a dose of 12 mg/kg/12 h for 3 days. The fourth day a blood analysis showed white blood cell 10.8 10/L with 0.45% CD34 cells and the patient was transferred to the pediatric intensive care unit for close monitoring during the LVL. The right jugular vein and the right femoral vein were canalized using the Seldinger’s technique with 4F single lumen arterial catheters (Plastimed). They allow a very good flow (30 to 40mL/h) without collapsing and without hemolysis and they are thin and short enough for very small children, but they are very rigid and have to be placed immediately before apheresis. A double lumen dialysis catheter (7F) was considered too big for our patient. The Cobe Spectra was primed with irradiated and leukodepleted RBCs diluted with fresh frozen plasma to an hematocrit identical to that of the patient (30%). When priming finished, heparin (1mg/kg) was administered to the patient and the procedure was started at an anticoagulant: inlet ratio of 1:24. The anticoagulant solution consisted of citric acidcitrate-dextrose (ACD) plus heparin (3000 IU heparin/500mL ACD-A). Initial access flow was 10.8mL/min, in the range recommended by the manufacturer for optimal function (10 to 85mL/min). After 3 blood volumes had been processed the proportion was further reduced to 1:30 increasing access flow to 13.5mL/min. No platelet clumping or aggregates were observed. ACD (5mL) were added to the collection bag to prevent clotting of the product. Sedation and analgesia is probably necessary in all infants for patient confort and to avoid accidental extraction of the catheter or vein injury with the patient’s movements. It was initially attempted with fentanyl in continuous infusion (2 mg/kg/h). However, the infant was very anxious and agitated and midazolam was added in increasing doses until achieving enough sedation, but the patient had to be intubated because of respiratory depression. Other alternatives include propofol (2 to 4mg/kg/h) and remifentanyl (0.05 to 0.15 mg/kg/h). A calcium drip (10mL calcium gluconate in 500mL normal saline at an infusion rate of 30mL/h) was administered during the procedure, and ionized calcium levels were periodically checked being normal all time. We did not use an in-line blood warmer. Instead, the patient was placed under a thermic lamp to avoid hypothermia. The procedure was uneventful and 6 blood volumes were processed in 4 hours obtaining a 36mL product with a CD34 content of 9.5 10/kg. The collection efficiency was 48.7%. In summary, PBSC collection by LVL with an automated procedure can be effectively and safely performed in a 7-kg infant. Careful planification and cooperation between hematologists and pediatric intensive care unit specialists is essential.