Acute oxygenator occlusion in two cases of polycythemia vera: Bailout strategies

Abstract Polycytemia vera (PV) is a rare myeloproliferative neoplasm associated with microcirculatory disturbances, thrombosis and bleeding. Patients suffering from PV have a high risk of perioperative adverse events, but the literature regarding on‐pump procedures in PV patients is scarce. We report two cases of acute and severe oxygenator failure during cardiopulmonary bypass and present valid exit scenarios.


| INTRODUCTION
Polycytemia vera (PV) is a rare myeloproliferative neoplasm which may, mostly late in the course of disease, transform into myeloid metaplasia with myelofibrosis or into leukemia. 1 Patient frequently report about microcirculatory disturbances, sometimes with erythromelalgia. Pruritus, and fatigue are also frequent symptoms and clinical investigation can reveal splenomegaly. Total red blood cell mass is significantly increased. Cell proliferation is typically independent of erythropoietin and a result of a mutation of JAK2 in hematopoietic progenitor cells. 2 While therapy is usually applied to reduce long-term complications, patients may have an increased cardiac risk profile including thrombosis and bleeding. 1,3 Phlebotomy or treatment with the chemotherapeutic agent hydroxyurea may be necessary to control hematocrit, white blood cell counts and platelet counts. 1 Furthermore, antiaggregative and antithrombotic therapy may be required.
Patients suffering from PV have a high risk of perioperative adverse events. 4 While several reports are available for noncardiac surgical procedures, the literature regarding on-pump procedures is scarce. 5 Cardiopulmonary bypass represents a severe change of hemodynamic conditions and specifically the oxygenator imposes high mechanical stress to the blood components. New generations of oxygenators have a very low risk of thrombosis due to their specific internal coating. 5 However, this may not be sufficient in patients with PV. We report two cases of acute and severe oxygenator failure and present valid exit scenarios.

| CASE 2
A 64-year-old female patient with severe aortic stenosis and severe mitral regurgitation was admitted for planned combined valve surgery. She was suffering from PV with a preoperative cell count of 4.7 × 10 6 /μL for red blood cell, 570 000/μL for thrombocytes and 11 500/μL for white blood cell. Current preoperative treatment for PV was ruxolitinib 5 mg in the morning and Ropeginterferon alfa-2b 250 mg twice per week. Due to the institutional experience with PV in previous cases, a back-up oxygenator was cut into the pump system before initiation of cardiopulmonary bypass ( Figure 2B). Total 500 mL of the patients own blood was drawn before normothermic cardiopulmonary bypass for hemodilution and reinfused after surgery. Preoperative ACT was 126 seconds, which increased to 512 seconds after 35 000 IE of heparin. However, ACT fell rapidly to 245 seconds after 25 minutes and a repeated dose of 15 000 IE was given. Tranexamic acid (1000 mg) was additionally administered before cardiopulmonary bypass. While a 27 mm Medtronic Mosaic F I G U R E 1 Perioperative pump flow (red) and oxygenator pressure gradient (blue). A, The first case revealed a rapid pressure gradient increase and was exchanges with a full pump stop, and a second clotting was observed. B, The second case had a back-up oxygenator, and the change could be performed without pump stop during cardiac surgery F I G U R E 2 Intraoperative images. A, Clotted oxygenator (case 1). B, Back-up oxygenator (case 2). C, Thrombotic adhesions found in pump tubes after surgery (case 2) 2836 | KAISER ET AL. biological valve was implanted, the oxygenator pressure increased and the system was switched to the back-up oxygenator ( Figure 1B). The surgery was continued by replacing the aortic valve with a rapiddeployment surgical bioprosthesis (Edwards Intuity Elite 19 mm). The surgery remained uneventful and the patient could be weaned from bypass without adverse events. Pump tubing showed severe thrombotic adhesions at the connection areas ( Figure 2C). Further postoperative course remained uneventful and the patient was discharged in good clinical condition.

| COMMENT
PV was previously identified as a risk factor during noncardiac surgery. 4 Furthermore, acute intracardiac thrombosis was reported during coronary artery bypass grafting. 6,7 Both patients presented herein are defined as PV patients with a high risk for thrombosis according to previous literature. 8  We report herein two additional PV patients with severe adverse events related to the oxygenator. The first patient had two episodes of rapid oxygenator closure, even after significant hemodilution and anticoagulation. Therefore, this patient was switched to a transfemoral approach, which was uneventful. The second patient required a combined aortic and mitral procedure and was therefore planned for surgery instead of a transfemoral approach. Due to our previous experience with PV during cardiopulmonary bypass, a back-up oxygenator was prepared and saved this patient from a severe adverse event during cardiopulmonary bypass.
We want to highlight the increased risk of patients suffering from PV and undergoing cardiac surgery. This risk seems to be not directly related to the actual blood cell count, but may also be induced by cell dysfunctions with increased clotting capability in these patients.
Hemodilution did not prevent a second oxygenator clotting in our experience. Currently, no verified method exists to predict clotting of the oxygenator in patients with PV. Furthermore, patients with PV may also present with an increased bleeding risk in the postoperative period. 9,10 Therefore, we recommend to apply transcatheter strategies when a comparable outcome can be expected. If cardiopulmonary bypass is required, a back-up oxygenator should be included in the pump system to be ready for rapid exchange.

ETHICS STATEMENT
The patients gave written informed consent to publish their cases.