Evaluation of a Respiratory Assist Catheter that Uses an Impeller Within a Hollow Fiber Membrane Bundle

Abstract

Respiratory assist using an intravenous catheter may be a potential treatment for patients suffering from acute or acute-on-chronic lung failure. The objective of this study was to evaluate a novel respiratory catheter that uses an impeller within the fiber bundle to enhance gas exchange efficiency, thus requiring a smaller fiber bundle and insertional size (25 Fr) and permitting simple percutaneous insertion. Bench testing of gas exchange in deionized water was used to evaluate eight impeller designs. The three best performing impeller designs were evaluated in acute studies in four calves (122 + or - 10 kg). Gas exchange increased significantly with increasing impeller rotation rate. The degree of enhancement varied with impeller geometry. The maximum gas exchange efficiency (exchange per unit surface area) for the catheter with the best performing impeller was 529 + or - 20 ml CO(2)/min/m(2) and 513 + or - 21 ml CO(2)/min/m(2) for bench and animal studies, respectively, at a rotation rate of 20,000 rpm. Absolute CO(2) exchange was 37 and 36 ml CO(2)/min, respectively. Active mixing by rotating impellers produced 70% higher gas exchange efficiency than pulsating balloon catheters. The sensitivity of gas exchange to impeller design suggests that further improvements can be made by computational fluid dynamics-based optimization of the impeller.

Effect of Impeller Design and Spacing on Gas Exchange in a Percutaneous Respiratory Assist Catheter

“…Rotation speed remains an important factor in active mixing, as was shown for all geometries tested previously (22). Other possible design parameters or arrangements that may contribute to gas exchange that were not investigated in this work are impeller length and driveshaft orientation relative to other impellers (i.e., whether the impeller is aligned with blades offset to neighboring impeller).…”

“…Pressure drop across the fiber bundle was monitored with differential transducers (143C; Honeywell International, Inc., Morristown, NJ, USA). We have shown previously that measured CO 2 removal in water bench testing correlates well with in vivo performance (within ~10%) for IPRAC devices, so for simplicity all testing was performed in deionized water at 37°C (22,23). Water flow rate was maintained at 3.0 L/min in the loop and monitored with a clamp-on ultrasonic flow probe (Transonic Systems, Inc., Ithaca, NY, USA).…”

“…Earlier work focused primarily on characterizing the relationship between rotation rate and gas exchange, as well as evaluation of eight different impeller designs. Not surprisingly, gas exchange correlated directly with rotation rate, and maximum CO 2 removal rates were achieved at the highest rate tested (20 000 rpm) (22). A strong dependence of gas exchange on impeller design was also observed.…”

Acidic sweep gas with carbonic anhydrase coated hollow fiber membranes synergistically accelerates CO2 removal from blood

“…Achieving clinically significant CO 2 removal at blood flow rates less than 500 mL/min remains a challenge. New technologies such as active blood mixing within gas exchange fiber bundles have improved CO 2 removal efficiency at low blood flow rates [23]–[25], but gas transport in ECCO 2 R devices is ultimately limited by the blood CO 2 partial pressure (PCO 2 ) gradient across hollow fiber membranes (HFMs) [26]. Our lung tissues face the same diffusional challenges as HFMs, however they employ the enzyme carbonic anhydrase (CA) within red blood cells and on the endothelial surfaces of lung capillaries to accelerate diffusion by catalyzing the reversible dehydration of HCO 3 − (bicarbonate) to gaseous carbon dioxide: ${\text{CO}}_2+{\mathrm{H}}_2\mathrm{normalO}\stackrel{CA}{\iff }{{\text{HCO}}_3}^{-}+{\mathrm{H}}^{+}$.…”

Extracorporeal Carbon Dioxide Removal: The Future of Lung Support Lies in the History

“…Improvisations in catheter design are being attempted to achieve at least 50% of gas exchange requirements. Among these, attempts to generate active mixing in the catheter include placement of an intra-aortic balloon pump in the vicinity of hollow fibers or rotation of the fiber bundle (dynamic intravascular lung assist devices) or positioning impellers to generate mixing [60,61]. In addition, biocatalysis achieved by immobilization of carbonic anhydrase on the surface of the fibers increases CO 2 liberation from bicarbonate and consequently may further promote increased CO 2 elimination by as much as 75% [62].…”