Essential thrombocytosis (ET) is a chronic myeloproliferative neoplasm characterized by the presence of thrombocytosis and it can be complicated by thrombotic and/or hemorrhagic events. Treatment options include low‐dose aspirin and cytoreductive agents such as hydroxyurea. In cases of extreme thrombocytosis, therapeutic thrombocytapheresis can be a useful procedure. We present a case of a 61‐year‐old‐man previously diagnosed with CALR‐mutated ET, who develop acute myeloid leukemia. When recovering after induction chemotherapy, he developed an extreme thrombocytosis up to 2337 × 109/L regardless hydroxyurea was started. Two therapeutic trombocytapheresis were performed and anagrelide was added to cytoreductive regimen. Platelet count stabilized around 570 × 109/L. Both procedures were performed with the Spectra Optia Apheresis System version 11.3 (Terumo BCT) and we decided to use a higher collection preference and lower collection speed than manufacturer's recommendations. Platelet count decreased from 2380 × 109/L to 1035 × 109/L in the first procedure and from 1813 × 109/L to 768 × 109 in the second procedure. Platelet collection efficiency was calculated to be 110.3% and 86.1% in the first and second thrombocytapheresis, respectively. Therapeutic thrombocytapheresis with Spectra Optia is a safe and efficient therapy to treat patients with primary thrombocytosis while effect of cytoreductive agents is attained. Platelet collection efficiency was calculated to be higher than previously reported. We suggest that changes in technical parameters such as a deeper aspiration point and/or lower collection speed may increase procedure's efficiency.

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BACKGROUND Peripheral venous access (PVA) devices for apheresis should be selected to provide enough flow with the least vein damage, but little information is available about PVA devices blood flow rates. The aim of this study was to know the blood flow rates provided by the most frequent PVA devices used in apheresis procedures. STUDY DESIGN AND METHODS An experimental study was designed to simulate a plasma exchange procedure using citrated whole blood (WB). Two steel needles (16‐ and 17‐gauge [G]) and six plastic cannulas (16G, 17G, two 18G, 20G, and 22G) were analyzed. The hematocrit of the WB was adjusted to 45%, 40%, 35%, 30%, and 25%. The separated plasma from the WB was used as replacement fluid. RESULTS Blood flow rate (inlet/return, mL/min) for 16G and 17G devices with a hematocrit of 45% was 142/142 (maximum admitted by separator); one of the 18G cannulas reached 142/142 and the other one reached 117/140; the 20G cannula reached 78/94; and the 22G reached 45/55. A hematocrit reduction from 45% to 25% increased the flow rate (when possible) over 22% (range: 14%‐30%). CONCLUSIONS PVA devices with a size of 16‐18G provided the maximum flow admitted by the apheresis system. The 20G provided flow rates for a significant number of procedures, and 22G could be used in some procedures. The hematocrit should be taken into account when selecting the PVA device since, at hematocrit of 25%, the flow can be from 14% to 30% higher than flow rates reached with blood at hematocrit of 45%.

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We report the case of a patient undergoing therapeutic plasma exchange (TPE) because of acute liver failure after hepatitis B virus infection in whom the unexpected proximity of the end tips of two central vein catheters led to perplexing laboratory results. The TPE was performed using a double-lumen catheter (Arrow Int.) placed in the right external jugular vein. The patient was simultaneously receiving a K 1 perfusion (320 mEq/L in 5% glucose; 42 mL/hr) through a triple-lumen catheter (Nordic Medcom) inserted into the left external jugular vein.While on the TPE, two consecutive blood samples drawn from the proximal lumen of the apheresis catheter yielded K 1 levels of 9.41 and 8.71 mEq/L (normal, 3.5-5.5 mEq/L), respectively. The plasma was clear, without any sign of hemolysis, the EKG registry was normal, and the K 1 level had been 2.76 mEq/L in a blood sample collected from the radial artery a little earlier. Although the high serum K 1 levels were disregarded as incongruent, the K 1 infusion was stopped and new From the