Impact of sweep gas flow on extracorporeal CO2 removal (ECCO2R)

Abstract

BackgroundVeno-venous extracorporeal carbon dioxide (CO2) removal (vv-ECCO2R) is increasingly being used in the setting of acute respiratory failure. Blood flow rates range in clinical practice from 200 mL/min to more than 1500 mL/min, and sweep gas flow rates range from less than 1 to more than 10 L/min. The present porcine model study was aimed at determining the impact of varying sweep gas flow rates on CO2 removal under different blood flow conditions and membrane lung surface areas.MethodsTwo different membrane lungs, with surface areas of 0.4 and 0.8m2, were used in nine pigs with experimentally-induced hypercapnia. During each experiment, the blood flow was increased stepwise from 300 to 900 mL/min, with further increases up to 1800 mL/min with the larger membrane lung in steps of 300 mL/min. Sweep gas was titrated under each condition from 2 to 8 L/min in steps of 2 L/min. Extracorporeal CO2 elimination was normalized to a PaCO2 of 45 mmHg before the membrane lung.ResultsReversal of hypercapnia was only feasible when blood flow rates above 900 mL/min were used with a membrane lung surface area of at least 0.8m2. The membrane lung with a surface of 0.4m2 allowed a maximum normalized CO2 elimination rate of 41 ± 6 mL/min with 8 L/min sweep gas flow and 900 mL blood flow/min. The increase in sweep gas flow from 2 to 8 L/min increased normalized CO2 elimination from 35 ± 5 to 41 ± 6 with 900 mL blood flow/min, whereas with lower blood flow rates, any increase was less effective, levelling out at 4 L sweep gas flow/min. The membrane lung with a surface area of 0.8m2 allowed a maximum normalized CO2 elimination rate of 101 ± 12 mL/min with increasing influence of sweep gas flow. The delta of normalized CO2 elimination increased from 4 ± 2 to 26 ± 7 mL/min with blood flow rates being increased from 300 to 1800 mL/min, respectively.ConclusionsThe influence of sweep gas flow on the CO2 removal capacity of ECCO2R systems depends predominantly on blood flow rate and membrane lung surface area. In this model, considerable CO2 removal occurred only with the larger membrane lung surface of 0.8m2 and when blood flow rates of ≥ 900 mL/min were used.

In vivo carbon dioxide clearance of a low-flow extracorporeal carbon dioxide removal circuit in patients with acute exacerbations of chronic obstructive pulmonary disease

“…The amount of CO 2 removed is higher for a blood flow of approximately 0.4 L/minute and a membrane surface areas of 0.59 m 2 than has been reported in previous studies, including those where membranes with larger surface areas were explored. [28][29][30] Furthermore, the amount of CO 2 removed also varies with the blood flow -for any given sweep flow, a higher blood flow results in a greater CO 2 clearance. 28 It is likely that this is due to the far higher PCO 2 in patients' venous blood than in the in vitro models as it is known that the PCO 2 and total CO 2 content in venous blood are important determinants of the CO 2 which can be removed.…”

“…[28][29][30] Furthermore, the amount of CO 2 removed also varies with the blood flow -for any given sweep flow, a higher blood flow results in a greater CO 2 clearance. 28 It is likely that this is due to the far higher PCO 2 in patients' venous blood than in the in vitro models as it is known that the PCO 2 and total CO 2 content in venous blood are important determinants of the CO 2 which can be removed. 29 Indeed, when the inlet PCO 2 is normalized, the VCO 2 is reduced, although the relationship between CO 2 clearance and sweep gas flow is maintained (Figure 1(b)).…”

Low-flow assessment of current ECMO/ECCO2R rotary blood pumps and the potential effect on hemocompatibility

“…In daily clinical practice, systems operating at blood flow rates up to 500 mL/min remove CO 2 on the order of 80 mL/min. This can be nearly doubled by doubling the blood flow rate, thereby accounting for approximately 50% of the CO 2 production of an adult resting intensive care unit (ICU) patient [19–22]. Furthermore, ECMO therapy for neonatal and pediatric patients uses comparable blood flow rates with current rotary blood pumps.…”

Evaluation of a New Extracorporeal CO2 Removal Device in an Experimental Setting

“…Animal data conflict with one another. Karagiannidis et al [ 11 , 12 ] demonstrated, using a porcine model, that a blood flow rate > 1 L/min with a membrane lung with a surface area > 0.8 m 2 may remove the 50% of total CO 2 production and correct severe respiratory acidosis. Contrarily, Duscio et al [ 10 ] reported a very high VCO 2 (171 mL/min) with a low blood flow (400 mL/min) and a high surface membrane lung (1.8 m 2 ).…”

“…Animal data, instead, were controversial. Duscio et al [ 10 ] reported very high CO 2 removal (171 mL/min) using a low-flow device (400 mL/min), while Karagiannidis et al [ 11 , 12 ] showed that only high blood flow rates (>900 mL/min) and adequate membrane lungs (surface area > 1 m 2 ) can effectively correct severe respiratory acidosis. However, both studies converge on the point that the sweep gas flow can increase CO 2 removal only when high blood flow rates are used.…”