Extracorporeal therapy was performed using Prismaflex or AK 200 devices (Gambro-Hospal; Meysieu, France). Blood flow was between 200 and 300 ml/min. The upper pressure alarm limit was 350 mm Hg on the outlet line of both ECT devices. Duration of plasmapheresis or hemodialysis sessions was 4 hours, and maximal recommended lifetime of the hemofilter during hemofiltration was 72 hours. Unfractioned heparin was used for anticoagulation, with a targeted anti-Xa between 0.2 and 0.4 IU/ml. Measures were recorded 1 hour after beginning ECT.
Twenty-one patients under ECMO support had ECT with connection to the circuit using our technique. Features of the patients are reported in Table 1. The average VA ECMO, VV ECMO, and ECT blood flows were 3.76 ± 0.86 L/min, 4.10 ± 0.83 L/min, and 234.0 ± 31.6 mL/min, respectively. The average lifetime of the hemofilter was 57.5 ± 24.0 hours. In 10 patients, the hemofilter reached its recommended duration time (72 hours). No ECT was interrupted for excessive circuit pressure. In all cases, serum urea decreased when renal replacement therapy was achieved. No severe complication, such as circuit disconnection, hemorrhage, air embolism, hemolysis with free bilirubinemia above 30 mmol/L, blood pressure drop at ECT initiation, or lower limb ischemia occurred during the study period.
The major interest of connecting ECT to an ECMO circuit is to avoid complications related to central venous catheter placement. Moreover, iterative undetected blood flow reductions related to catheter have been reported, with a shortened hemofilter lifetime.5
Some authors previously described different possibilities for ECT connection to the ECMO circuit. The most used is to connect both inlet and outlet lines between the pump and the oxygenator (alternate connection site No. 1, Figures 2 and 3). However, the main limitation of this technique is the high circuit pressure when ECMO blood flow rises above 3 to 3.5 L/min, hindering the ECT outlet flow. In that case, the only way to perform ECT is to decrease the ECMO blood flow, which could not be tolerated by the patient.
Others described ECT outlet line connection to the ECMO prepump line decreased outlet pressure6 (alternate connection site No. 2, Figures 2 and 3). However, the major issue of using the prepump line for any connection is a high risk of air entrapment in this negative-pressure part of the circuit. Moreover, pressure variations are high in this part of the ECMO circuit and could cause ECT iterative dysfunctions. Thus, a recently published work in adults using this technique reported a much lesser hemofilter duration time (22 hours) than we noticed.3
In all cases of ECT device connection to the ECMO circuit, the most challenging is to manage excessive outlet pressure. Thus, we connected the outlet line to the most distal point of the ECMO circuit, where according to Poiseuille’s law, pressure is the lowest. This part of the circuit corresponds to distal arterial perfusion cannula in VA ECMO or to venous return cannula in VV ECMO. The inlet line has to be connected to the oxygenator to provide oxygenated blood to the limb in VA ECMO and to avoid oxygenator shunt during VV ECMO. Our reported connection is safe for two main reasons. First, the embolic risk seems to be minimal with this technique because of the positive blood pressure of the ECMO circuit and the ECT device air detector. Second, blood flow through the distal perfusion cannula is at least equal to that would be observed without ECT, because backflow to the arterial cannula only occurs if its pressure is inferior to distal perfusion cannula pressure. Thus, no limb ischemia occurred in patients under VA ECMO support. The main risk of this technique is the ECT accidental disconnection, with subsequent severe bleeding. For this reason, we recommend ECT connection and disconnection under senior physician supervision. The main limitations are the need for a distal perfusion cannula when used in VA ECMO or very high ECMO blood flows (i.e., above 6 L/min) with subsequent high and difficultly predictable pressures. In that case, pressure measurement before connection is recommended.
In conclusion, connecting an ECT device to the distal perfusion cannula during VA ECMO or to the venous return cannula during VV ECMO is simple, effective, and costless. Because high pressures management remains challenging, we suggest the present technique as first choice for ECT device connection in ECMO patients.
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3. de Tymowski C, Augustin P, Houissa H, et al. CRRT connected to ECMO: managing high pressures. ASAIO J 2017.63: 48–52.
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during extracorporeal membrane oxygenation
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Keywords:Copyright © 2018 by the American Society for Artificial Internal Organs
extracorporeal membrane oxygenation; renal replacement therapy; plasmapheresis