Virchow’s triad of stasis, vascular damage, and hypercoagulability contribute to thrombosis. Although patients on extracorporeal membrane oxygenation (ECMO) are usually on pharmacologic anticoagulation (i.e., heparin), it’s still possible to form clots in areas of sluggish flow such as Y-connectors and the membrane oxygenator.
When I’m inspecting a circuit, I use a flashlight to assess for focal areas of clot formation which look like black spots as seen in the image. The upstream side of the oxygenator (specifically the corners) is usually where I find clots; however, one should carefully inspect both sides and the rest of the circuit. I’m especially concerned for clot formation in patients with hypercoagulable conditions such as a malignancy or situations in which the ECMO flow is low due to poor drainage, suboptimal cannula position, etc.
At a given pump speed, the pressure gradient across the oxygenator (ΔP) will start to increase as the clot burden worsens. Consequently, the ECMO flow may drop as more “work” is needed to overcome the increasing resistance. Conversely, if the pump speed is increased to improve flow, one runs the risk of increased hemolysis and “chattering” of the drainage line. Ultimately, the circuit may need to be changed.