CO₂ clearance by membrane lungs

Abstract

Introduction Commercial membrane lungs are designed to transfer a specific amount of oxygen per unit of venous blood flow. Membrane lungs are much more efficient at removing CO2 than adding oxygen but the range of CO2 transfer is rarely reported. Methods Commercial membrane lungs were studied with the goal of evaluating CO2 removal capacity. CO2 removal was measured in 4 commercial membrane lungs under standardized conditions. Conclusion CO2 clearance can be greater than 4 times that of oxygen at a given blood flow when the gas to blood flow ratio is elevated to 4:1 or 8:1. The CO2 clearance was less dependent on surface area and configuration than oxygen transfer. Any ECMO system can be used for selective CO2 removal.

In-vitro performance of a low flow extracorporeal carbon dioxide removal circuit

“…18,19 Although the relationship between CO 2 clearance is effectively linear in healthy humans varying directly with changes in minute ventilation, pulmonary blood flow and CO 2 content, the relationship between CO 2 clearance and both blood and sweep gas flow in this extracorporeal circuit is highly sensitive to changes in gas flow rate at low gas flow rates, but becomes less sensitive at high sweep flow rates, similar to other reports in the literature. 8–10,20–23 Compared with the reported CO 2 clearance from other devices, the clearance at low sweep gas flows (1-2L/minute) is similar, however the maximum CO 2 clearance is not as high as that seen in devices with blood flow over 1L/minute, although all reach a plateau at a ventilation to perfusion ratio of 10:1. 8–10,20–23 To gain further increases in CO 2 clearance, an increase in blood flow is required.…”

“…8–10,20–23 Compared with the reported CO 2 clearance from other devices, the clearance at low sweep gas flows (1-2L/minute) is similar, however the maximum CO 2 clearance is not as high as that seen in devices with blood flow over 1L/minute, although all reach a plateau at a ventilation to perfusion ratio of 10:1. 8–10,20–23 To gain further increases in CO 2 clearance, an increase in blood flow is required. 7,24–26…”

“…7 These same factors affect membrane clearance of CO 2 in vivo as do technical factors including sweep gas flow rate, blood flow through the membrane, ventilation/perfusion matching within the membrane, membrane surface area. 8 Furthermore, the relationship between CO 2 clearance and both blood and sweep gas flow in extracorporeal circuits is known to be non-linear. 8 For any given blood flow rate, at low sweep flow rates, CO 2 clearance is highly sensitive to changes in gas flow rate, but at high sweep flow rates clearance becomes less sensitive.…”

“…8 Furthermore, the relationship between CO 2 clearance and both blood and sweep gas flow in extracorporeal circuits is known to be non-linear. 8 For any given blood flow rate, at low sweep flow rates, CO 2 clearance is highly sensitive to changes in gas flow rate, but at high sweep flow rates clearance becomes less sensitive. 9,10 This is less apparent in high blood flow devices as the clearance of CO 2 tends to plateau above a ventilation/perfusion ratio of 10:1.…”

A mock circulation loop to test extracorporeal CO2 elimination setups

“…The impact of the sweep gas flow (air) on CO 2 removal and the relationship between and dead space was investigated [ 7 ]. Moreover, Sun et al tested four commercial MLs in a closed loop circuit with one centrifugal pump [ 12 ]. The CO 2 removal rates for the tested Maquet Quadrox pediatric iD MLs were in the same range as our results using the same ML for a Hb of 15 g/dL (Table 3 ).…”