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

Abstract

Introduction: Extracorporeal gas exchange requires the passage of oxygen and carbon dioxide (CO2) across an artificial membrane. Current European Union regulations do not require the transfer to be assessed in models using clinically relevant haemoglobin, making it difficult for clinicians to understand the CO2 clearance of a membrane, and how it changes in relation to sweep gas flow through the membrane. The characteristics of membrane CO2 clearance are described using a single membrane at different sweep gas flows in an in vitro model with clinically relevant haemoglobin concentrations using three separate methods of calculating CO2 clearance. Methods: To define the CO2 removal characteristics of the extra-corporeal CO2 removal (ECCO2R) device, we devised an in-vitro gas exchange circuit formed by a dedicated ECCO2R circuit (ALung, Pittsburgh, USA) in series with two membrane oxygenators. The system was primed with donated expired human red cells provided by the local blood bank. The experimental set-up allowed constant CO2 input (via one membrane oxygenator) with variable removal from a portion of the blood in a manner which was analogous to that seen in vivo. Blood gases were measured from different ports in the circuit in order to measure the experimental membrane CO2 clearance (VCO2). Results: Results demonstrate that the relationship between VCO2 and gas flow at a constant blood flow of 0.4 L/minute with a haemoglobin of 7 g/dL increases sharply from a gas flow of 0 to 2 L/min but plateaus at gas flows >4 L/minute. VCO2, calculated using three different methods, showed a strong linear correlation with minimal bias. Conclusions: The CO2 clearance of the membrane used in this bench test is non-linear. This has implications for clinical practice, especially during the weaning phase of the device.

A mock circulation loop to test extracorporeal CO2 elimination setups

“…Therefore, an efficient mobile ECCO 2 R with limited sweep gas supply should stay at the lower sweep gas flow rates of this plateau. Similar results have been shown by Barret et al for a blood flow of 400 mL/min and a plateau forV Sweep ≥ 4 L/min [7].…”

“…Barret et al demonstrated a low blood flow single loop ECCO 2 R model and used a Hemolung test ML. 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 ].…”

“…As an alternative, MLs can be tested in mock circuits. Different mock designs have been described in the literature [ 7 – 10 ]. The aim of our study is to present a new mock circuit that reflects the anatomy of a mammal body connected to an ECCO 2 R more closely and to validate that mock in three experimental scenarios.…”

Update on extracorporeal carbon dioxide removal: a comprehensive review on principles, indications, efficiency, and complications

“…44,45 A recent experimental model of ECCO 2 R showed an effective CO 2 removal strongly dependent on sweep gas flow up to about 5 L/min, when a plateau was reached not leading to a relevant increase in CO 2 elimination with higher sweep gas flows. 46 Indications for ECCO 2 R ARDS ECCO 2 R has been originally used to enable less invasive mechanical ventilation in patients suffering from ARDS. 7 At that time (1986), lung protection was thought to be a matter of respiratory rate and a plateau pressure below 45 cmH 2 O.…”

Impaired membrane lung CO2 elimination: is it dead space, V/Q ratio or acidosis?

“…According to their simulator setup, the blood gas sample for V D calculation was taken before the oxygenator for which V D was to be calculated. For correct dead space fraction calculation, post membrane or arterialized CO 2 partial pressure (P pm CO 2 ) and exhaust pCO 2 should be used 2,3…”