A double catheter approach for extracorporeal CO₂ removal integrated within a continuous renal replacement circuit

After the avian flu epidemic in 2009, oxygenation-improving techniques such as extracorporeal membrane oxygenation (ECMO) and extracorporeal CO₂ removal (ECCO₂R ) gained momentum considerably.[1] ECCO₂R systems in particular earned increasing clinical appeal as adjuvant therapy of the acute respiratory distress syndrome (ARDS) and chronic obstructive pulmonary disease (COPD). ECCO₂R allowed safe application of ultra-protective ventilation in ARDS and improved PaCO₂, pH, and minute ventilation in COPD patients.[2] The basic physiological concept of ECCO₂R was already elaborated in the late seventies.[3] Since then, technical progress has made giant steps evolving from spontaneous arterio-venous to pump-driven veno-venous ECCO₂R, and finally, the embedding of ECCO₂R within a continuous renal replacement therapy (CRRT) circuit.[4]

Blood flow is an important factor that may limit optimal CRRT-ECCO₂R use. Some patients require a blood flow of 450 mL/min in order to achieve significant CO₂ removal to assure a pH above 7.2.[5] In many cases, such high blood flow can only be maintained for 24 h,[6] even when up to 16 Fr double lumen catheters are used. These large-bore catheters are also mostly armored and expensive. The amount of removed CO₂ dramatically declines when blood flow decreases to 300–350 mL/min. CO₂ elimination then becomes more dependent upon sweep gas flow rather than blood flow.[7]

In the intensive care unit of the Brugmann University Hospital, we developed a novel and cost-saving approach that enables to run ECCO₂R integrated within a CRRT circuit at a 450 mL/min blood flow for 48 h to 72 h. Briefly, two double-lumen catheters were inserted in a jugular vein and in a femoral vein respectively. Both catheters were 13 Fr sized and 25 cm long (GamCath^®, Gambro, Lund, Sweden). Adapting a similar approach as for veno-venous ECMO,[8] blood was extracted from the CRRT-ECCO₂R system via the femoral catheter and, after decarboxylation, reinfused through the cephalic catheter. The lumina of the double-lumen catheters were linked by a y-adapter to create a single blood line without loss of blood flow. Compared with the single catheter approach, access pressures measured in the Prismaflex® (Baxter, Illinois, ISA), were reduced by 40%, which allowed, as previously reported in case studies, an almost 40% increase in blood flow.[7] Some centers have used this double catheter technique on specific occasions and only when a single approach was found to be ineffective. The true originality of our approach lies in the systematic implementation of the double catheter technique in all CRRT-ECCO₂R-treated patients. Significant improvements in the pressure regimen and circuit rheology permitted to run CRRT-ECCO₂R for at least 48 h and, in the majority of cases, for up to 72 h.

No increased incidence of bleeding or catheter-related infection was observed with this double catheter approach. Of importance is that diluted citrate anticoagulation should be avoided when performing CRRT-ECCO₂R with the Prismaflex® device. A blood flow of 450 mL/min will dramatically increase citrate flow. This may cause an unwarranted increase in transmembrane pressure and a more pronounced pressure drop which promotes filter clogging and compromises filter lifespan.[9] Moreover, an increased citrate flow can enhance the risk of citrate intoxication.[10] Unfractionated heparin therefore is the preferred anticoagulation approach. It remains to be determined whether concentrated citrate could be an acceptable surrogate.[11]

In conclusion, a double catheter approach to integrate ECCO₂R within a CRRT circuit guarantees optimal and prolonged removal of CO₂. Our experience in more than 50 treated patients learns that the technique is safe and cost-effective.