Connecting continuous renal replacement therapy in parallel with extracorporeal membrane oxygenation: is there no problem?

Abstract

To the Editor: We read with great interest the article by Santiago et al. The continuous renal replacement therapy (CRRT) device functioned correctly after connecting with the extracorporeal membrane oxygenation (ECMO) circuit in parallel, not in series. Previously we observed different problematic pressures in connecting the CRRT device with the ECMO circuit in adults and children. It is clear from this article that the low blood flow rate of the CRRT device drained from the ECMO circuit will trigger the ‘arterial line disconnection’ alarm, owing to the positive inlet pressure exceeding the normal range. How can we ignore a prior warning of the Food and Drug Administration in 2005 on the potential risk of fluid imbalance in a Prisma device by allowing the alarm to be silenced repeatedly? Therefore, the real fluid removal from the CRRT device should be measured to make sure an accurate balance. When we tried the same connection system in adults, the normal blood flow (150ml/min) of the CRRT device avoided alarm because of difficulty in blood extraction, but not in blood return. Actually, the high resistance within the ECMO circuit following the centrifugal pump hindered the outlet flow of the CRRT device. Again, the on-line monitoring of pressure became an obstacle. It is not recommended to override the alarm, owing to the potential risks of hemolysis and filter clotting. Difficulty in finding vascular access for renal replacement therapy is a common problem in critically ill patients, especially in children. Thus, the utility of the ECMO circuit might be an alternative solution. However, it is inappropriate to conclude that inclusion of the CRRT device in the ECMO circuit is safe and effective without any complications in all patients.