Supplementary Material for: Continuous Renal Replacement Therapy during Extracorporeal Membrane Oxygenation: Circuit Haemodynamics and Circuit Failure

Introduction: Treatment with Continuous Renal Replacement Therapy (CRRT) is common during Extracorporeal Membrane Oxygenation (ECMO). Such ECMO-CRRT has specific technical characteristics, which may affect circuit life. Accordingly, we studied CRRT haemodynamics and circuit life during ECMO. Methods: ECMO and non-ECMO CRRT treatments in two adult intensive care units (ICUs) were compared using data collected over a 3-year period. A potential predictor of circuit survival identified in a 60% training data subset as a time-varying covariate within a Cox-proportional Hazards model, was subsequently assessed in the complementary remaining data (40%). Results: Median [interquartile range] CRRT circuit life was greater when associated with ECMO (28.8 [14.0-65.2] vs 20.2 [9.8-40.2] hours, p < 0.0001). Access, return, pre-filter and effluent pressures were also greater during ECMO. Higher ECMO flows were associated with higher access and return pressures. Classification and regression tree analysis identified an association between high access pressures and accelerated circuit failure, while both first access pressures ≥190mmHg (HR 1.58 [1.09 - 2.30]) and patient weight (HR 1.85 [1.15-2.97] third tertile vs first tertile) were independently associated with circuit failure in a multivariable Cox model. Access dysfunction was associated with a stepwise increase in trans-filter pressure, suggesting a potential mechanism of membrane injury. Conclusion: CRRT circuits used in conjunction with ECMO-have a longer circuit life than usual CRRT despite exposure to higher circuit pressures. Markedly elevated access pressures, however, may predict early CRRT circuit failure during ECMO, possibly via progressive membrane thrombosis as evidenced by increased trans-filter pressure gradients.