Patients receiving extracorporeal membrane oxygenation (ECMO) often require continuous renal replacement therapy (CRRT). The intra-circuit pressure of adult ECMO usually deviates from the physiological range. We investigated the use of CRRT connected to an ECMO circuit with physiological intra-circuit pressures (0-150 mmHg, defined as the "safety range") using an in vitro experiment involving a water-filled ECMO circuit. The intra-circuit pressure pre-pump, post-pump, and post-oxygenator were measured while varying the height of the pump or ECMO flow. The bypass conduit pressure and distance from the post-oxygenator port were measured to find the "safety point", where the bypass pressure remained within the safety range. Both drainage and return limbs of the CRRT machine were connected to the safety point and the inlet and outlet pressures of the hemofilter were recorded while varying the ECMO and CRRT flow. The pre-pump pressure only remained within the safety range for heights >75 cm (ECMO flow = 4 L/min) or ECMO flow <3.5 L min (height = 50 cm). The post-pump and post-oxygenator pressure was generally outside of the safety range. The bypass pressure decreased according to the distance from the post-oxygenator port and the safety point was found at 60 or 75 cm (in a 90-cm length conduit) regardless of ECMO flow. The hemofilter inlet and outlet pressures remained within the safety range for all conditions of ECMO and CRRT flow, findings validated in clinical cases. The bypass conduit within an ECMO circuit can be connected to a CRRT machine safely under physiological pressures in adult patients receiving ECMO.
Keywords: Adult; Bypass conduit; Continuous renal replacement therapy; Extracorporeal membrane oxygenation; Pressure.