“Low-flow” versus “mid-flow” extracorporeal CO2 removal: A review of clinical performance and device efficiency

25 November 2015 White Papers

By ALung Technologies

The impact of CO2 removal rate during extracorporeal carbon dioxide removal (ECCO2R) on clinical outcomes has not been well characterized in the literature. Furthermore, the effect of blood flow rate on CO2 removal efficiency is often misunderstood as it can vary widely from device to device. The purpose of this white paper is to characterize the effects of blood flow rate on CO2 removal for commercially available veno-venous ECCO2R devices (Hemolung RAS, ALung Technologies; iLA Activve, Novalung) using data from recently published clinical studies.

Study details

Data from recently published clinical studies1,2 utilizing veno-venous ECCO2R in the setting of ARDS or COPD were reviewed. Reported CO2 removal rates were analyzed where direct comparison between devices was appropriate, considering PaCO2 levels, timing of data collection after ECCO2R initiation, and device operational parameters.


CO2 removal rates for the Hemolung RAS (Qb = 428 mL/min; n=18), and iLA Activve (Qb = 1000 mL/min, 1500 mL/min; n=10) are shown in Figure 1.  Median CO2 removal rates were similar for all devices, despite a 3-fold difference in blood flow rates (428 – 1500 mL/min) across the tested devices. Device efficiency was characterized by normalizing CO2 removal rates to the blood flow rates (Figure 2). The low-flow ECCO2R system (Hemolung RAS) demonstrates a CO2 removal efficiency more than twice that of the mid-flow ECCO2R system (iLA Activve).

Figure 1: CO2 removal performance of low-flow (Hemolung RAS) versus mid-flow (iLA Activve) ECCO2R systems

Figure 1: CO2 removal performance of low-flow (Hemolung RAS) versus mid-flow (iLA Activve) ECCO2R systems

Figure 2: Relative CO2 removal rates

Figure 2: Relative CO2 removal rates

How much CO2 removal is necessary?

As evidence for ECCO2R continues to develop, different technological approaches have emerged, providing fractional to full CO2 removal depending on the configuration of the extracorporeal circuit. Most recent studies have utilized low-flow and mid-flow devices to provide partial extracorporeal CO2 removal on the order of 80-90 mL/min, representing 30-40% of metabolic production. This amount of carbon dioxide removal has been shown to be clinically effective for preventing intubation and mechanical ventilation in COPD patients1, and facilitating ultraprotective ventilation strategies for patients with moderate ARDS3.

Why does CO2 removal efficiency matter?

Carbon dioxide removal by an ECCO2R device is predominantly limited by the rate of CO2 diffusion through the blood boundary layer which exists directly adjacent to the gas exchange membrane surface. Gas exchange efficiency can be enhanced by increasing the velocity of the blood next to the membrane in order to disrupt the boundary layer. Unlike traditional ECMO oxygenators adapted for ECCO2R, the Hemolung RAS incorporates patented technology to locally accelerate the blood flow around the membrane, enhancing CO2 removal (Figure 4). The result is a highly efficient ECCO2R device capable of operating at blood flow rates 2-3 times lower than mid-flow devices. As a result, the Hemolung RAS can provide clinically-effective CO2 removal at dialysis-like blood flow rates using a smaller catheter and membrane surface area than other devices (Figure 3).

Figure 3: Scaled comparison of catheter and membrane surface area.

Figure 3: Scaled comparison of catheter and membrane surface area.


Analysis of published clinical studies using approved veno-venous ECCO2R devices shows that the Hemolung RAS can provide the same amount of CO2 removal as traditional “mid-flow” ECCO2R devices. The Hemolung ActivMixTM technology enables clinically significant CO2 removal at blood flow rates 2-3X less than other ECCO2R systems. Smaller venous catheters, similar in size to those used for dialysis, can be used with the Hemolung RAS. Partial carbon dioxide removal of 80-90 mL/min can be achieved with this minimally-invasive approach, helping COPD patients avoid intubation when NIV fails, and facilitating ultraprotective ventilation strategies for ARDS patients.

Figure 4: The Hemolung ActivMix Technology

Figure 4: The Hemolung ActivMix Technology


  1. Burki NK, Mani RK, Herth FJF, et al. A Novel Extracorporeal CO2 Removal System: Results of a Pilot Study of Hypercapnic Respiratory Failure in Patients With COPD. CHEST Journal 2013;143:678-86.
  2. Hermann A, Riss K, Schellongowski P, et al. A novel pump-driven veno-venous gas exchange system during extracorporeal CO-removal. Intensive Care Med 2015.
  3. Parrilla F, Bergesio L, Aguirre-Bermeo H, et al. Ultra-low tidal volumes and extracorporeal carbon dioxide removal (Hemolung RAS) in ARDS patients. A clinical feasibility study. Intensive Care Medicine Experimental 2015;3:A7.

About the Hemolung RAS

The Hemolung RAS from ALung Technologies provides Respiratory Dialysis®, a simple, minimally-invasive form of extracorporeal carbon dioxide removal (ECCO2R). The system utilizes patented technology to provide highly efficient CO2 removal at dialysis-like blood flow rates which are achieved through a single 15.5 Fr venous catheter. For more information, please visit https://old.alung.com.

Download a PDF of this white paper.

HL-PL-0328_RA. © ALUNG TECHNOLOGIES, INC. 2015. All rights reserved. ALung, Hemolung, Respiratory Dialysis, and ActivMix are registered trademarks of ALUNG TECHNOLOGIES, INC. Other products and company names mentioned herein may be the trademarks of their respective owners.