Hemolysis at low blood flow rates: in-vitro and in-silico evaluation of a centrifugal blood pump.

BACKGROUND: Treating severe forms of the acute respiratory distress syndrome and cardiac failure, extracorporeal membrane oxygenation (ECMO) has become an established therapeutic option. Neonatal or pediatric patients receiving ECMO, and patients undergoing extracorporeal CO2 removal (ECCO2R) represent low-flow applications of the technology, requiring lower blood flow than conventional ECMO. Centrifugal blood pumps as a core element of modern ECMO therapy present favorable operating characteristics in the high blood flow range (4 L/min-8 L/min). However, during low-flow applications in the range of 0.5 L/min-2 L/min, adverse events such as increased hemolysis, platelet activation and bleeding complications are reported frequently. METHODS: In this study, the hemolysis of the centrifugal pump DP3 is evaluated both in vitro and in silico, comparing the low-flow operation at 1 L/min to the high-flow operation at 4 L/min. RESULTS: Increased hemolysis occurs at low-flow, both in vitro and in silico. The in-vitro experiments present a sixfold higher relative increased hemolysis at low-flow. Compared to high-flow operation, a more than 3.5-fold increase in blood recirculation within the pump head can be observed in the low-flow range in silico. CONCLUSIONS: This study highlights the underappreciated hemolysis in centrifugal pumps within the low-flow range, i.e. during pediatric ECMO or ECCO2R treatment. The in-vitro results of hemolysis and the in-silico computational fluid dynamic simulations of flow paths within the pumps raise awareness about blood damage that occurs when using centrifugal pumps at low-flow operating points. These findings underline the urgent need for a specific pump optimized for low-flow treatment. Due to the inherent problems of available centrifugal pumps in the low-flow range, clinicians should use the current centrifugal pumps with caution, alternatively other pumping principles such as positive displacement pumps may be discussed in the future.

Crucial Aspects for Using Computational Fluid Dynamics as a Predictive Evaluation Tool for Blood Pumps.

The suitability of computational fluid dynamics (CFD) as a regulatory tool for safety assessment of medical devices is still limited: A lack of standardized validation and evaluation methods impairs the quantitative comparability and reliability of simulation studies, particularly regarding the assessment of hemocompatibility. This study investigated important aspects of validation and verification for three common turbulence modeling approaches (laminar, k-ω shear stress transport [SST] and stress-blended eddy simulation [SBES]) and three different mesh refinements. Simulation results for pressure head, characteristic velocity, and shear stress for the benchmark blood pump model of the Food and Drug Administration critical path initiative were compared with its published experimental results. For the highest mesh resolution, all three models predicted the hydraulic pump characteristics with a relative deviation averaged over six operating conditions below 6.1%. In addition, the SBES model showed an accurate agreement of the characteristic velocity field in the pump's diffusor region (relative error <2.9%), while the laminar and SST model calculated significantly elevated and deviating velocity amplitudes (>43.6%). The ability to quantify shear stress is fundamental for the prediction of blood damage. In this respect, this study demonstrated that: 1) a close agreement and validation of both pressure head and characteristic velocity was feasible and 2) the shear stress quantification demanded higher near-wall mesh resolutions, although such high resolutions were not required for the validation of only pressure heads or velocity. Hence, a mesh verification analysis for shear stresses may prove significant for the development of credible CFD blood damage predictions in the future.