Abstract With the recent advances in computer technology, computational fluid dynamics ( CFD s) has become an important tool to design and improve blood‐contacting artificial organs, and to study the device‐induced blood damage. Commercial CFD software packages are readily available, and multiple CFD models are provided by CFD software developers. However, the best approach of using CFD effectively to characterize fluid flow and to predict blood damage in these medical devices remains debatable. This study aimed to compare these CFD models and provide useful information on the accuracy of each model in modeling blood flow in circulatory assist devices. The laminar and five turbulence models (Spalart‐Allmaras, k‐ε (k‐epsilon), k‐ω (k‐omega), SST [Menter's Shear Stress Transport], and Reynolds Stress) were implemented to predict blood flow in a clinically used circulatory assist device, the C entri M ag centrifugal blood pump. In parallel, a transparent replica of the C entri M ag pump was constructed and selected views of the flow fields were measured with digital particle image velocimetry ( DPIV ). CFD results were compared with the DPIV experimental results. Compared with the experiment, all the selected CFD models predicted the flow pattern fairly well except the area of the outlet. However, quantitatively, the laminar model results were the most deviated from the experimental data. On the other hand, k‐ε renormalization group theory models and Reynolds Stress model are the most accurate. In conclusion, for the circulatory assist devices, turbulence models provide more accurate results than the laminar model. Among the selected turbulence models, k‐ε and Reynolds Stress Method models are recommended.
Case Reports: V-V ECMO has been utilized as a bridge to lung transplant and is becoming more common as a treatment for ARDS. The average duration of ECMO for this population is often 14 -21 days. We recently managed a patient for 155 days on V-V ECMO until bilateral lung transplantation was performed. The patient developed acute respiratory failure and ARDS from a wound infection. A 22 year old female was readmitted after Cesarean section and treated for a wound infection yet developed worsening fevers and progressive shortness of breath. Broad spectrum antibiotics were started and the patient intubated. A CT scan demonstrated ARDS. The patient further decompensated and was unresponsive to maximal mechanical ventilator support. V-V ECMO was emergently initiated at the bedside via percutaneous cannulation of the right internal jugular vein with a 21- French arterial cannula and right femoral vein with a 25- French venous cannula. The patient's oxygenation immediately improved. However the patient's course was further complicated by both increased mixing leading to hypoxia and progressive right ventricular dysfunction. This necessitated converting the peripheral ECMO cannulation to right atrial to pulmonary artery central cannulation. Attempts to wean off ECMO support failed. Follow up CT scans showed worsening lung injury with widespread fibrosis and consolidation with extensive traction bronchiectasis. The hope for recovery waned and the patient was listed for pulmonary transplant. During the waiting period the patient was removed from the ventilator and underwent aggressive physical therapy. 155 days after the initiation of V-V ECMO the patient successfully underwent a bilateral lung transplant on cardiopulmonary bypass with postoperative plasmapheresis. This case demonstrated the expanded role of ECMO in the management and support of respiratory failure. It can be initiated emergently as a bridge to decision, can be liberally offered to patients with no prior history of respiratory failure, and can be successfully utilized as a long term bridge to transplant as we continue to expand the time course of that bridge.
