Fibrin Sheath(s) During and After an ECMO Run: Be Suspicious!

A 28 year old lady experienced acute asthma exacerbation precipitated by the inhalation of a recreational drug (“Kobret”). She presented with ultra-severe hypercapnia and associated acidosis due to refractory bronchospasm (193.4 mm Hg and 6.857 at nadir, respectively), requiring veno-venous femoro-femoral extracorporeal membrane oxygenation (V-V ECMO). The patient received a loading dose of unfractioned heparin at cannulation, and a continuous intravenous infusion was started immediately after, with target activated clotting time 200’. No risk factors for thrombophilic states were know. In the first hours after ECMO initiation, a large white appearing deposit was detected on the arterial side of the membrane lung (Figure 1, see Video 1, Supplemental Digital Content) through flashlight test. Visual monitoring of venous side was unfeasible. The membrane lung internal resistances (MLR),1 720 dynes/sec/cm−5 at first assessment, where definitely higher compared with the initial resistances usually observed with the circuit in use; gas exchange was not affected (see Supplemental Digital Content 1, https://links.lww.com/ASAIO/A990). Over the days, deposit size decreased at a visual monitoring, as MLR, but multiple episodes of severe drainage insufficiency complicated an otherwise uneventful run, despite proper cannula position, relatively low flow and optimization of volume status.Figure 1.: Findings on the membrane lung during and after the ECMO run. A: White appearing deposit extending from the top corner on the arterial side of the membrane lung since the first hours after extracorporeal support initiation. B: Arterial side of the ML after ECMO weaning and blood evacuation. C: Venous side of the ML after ECMO weaning, blood evacuation, and disassembling of the ML/pumphead unit; an extensive sheat of opalescent deposit, supposed to be fibrin/proteinaceous material with embedded platelets, blood cells, according to existing literature, covers the polymethylpentene hollow fibers. Small sized red thrombi are also visible embedded in the white deposit, mostly at the center of the venous side of the ML (lower blood flow/higher turbulence area of the device). D: Close-caption of venous side of the membrane lung; blue arrows: sparse hollow fibers free from deposits. ECMO, extracorporeal membrane oxygenation; ML, membrane lung.At ECMO weaning, the circuit ML/centrifugal pumphead block was disassembled, revealing a large opalescent deposit covering a large portion of the surface of the venous side of the ML (Figure 1).2,3 Moreover, after cannula removal, point of care ultrasound (POCUS) revealed a large floating sheath running in inferior vena cava (IVC) (Figure 2; See Video 2, Supplemental Digital Content). A thoraco-abdominal contrast enhanced computed tomography (CECT) confirmed the presence of tubular-shaped filling defects in IVC (Figure 3), without signs of pulmonary embolism. Appearance was consistent with the so-called “fibrin sheath.”4,5Figure 2.: Ultrasonographic finding of a large floating tubular structure (“sheat,” blue arrows) in the inferior vena cava after cannula removal. A: Transthoracic echocardiography, subcostal view long axis. B: Transthoracic echocardiography, subcostal view short axis. C: Transhepatic ultrasonography, long axis; white arrow: thrombus-like structure embedded in the floating sheath. D: Transesophageal echocardiography, short axis.Figure 3.: Slice from the early venous phase of a contrast enhanced computed tomography demonstrating a tubular shape filling defect in the inferior vena cava above renal veins (blue arrows).These finding stress the need to strictly monitor circuit and vessels for complications during the run; looking for cannulation-related vascular complications is also pivotal after decannulation.