BIO12: Toward a Wearable Extracorporeal CO2 Removal System with Integrated Exhaust Gas CO2 Sensing

Purpose: Extracorporeal membrane oxygenation (ECMO) and extracorporeal carbon dioxide removal (ECCO2R) have been used frequently in the last ten years to treat patients with severe respiratory failure. These therapeutic strategies mitigate the complications associated with invasive mechanical ventilation. Further, concurrent ambulatory and physical therapy is demonstrated to improve patient outcomes, reduce hospital cost, and enhance patient quality-of-life. However, the complexity of these extracorporeal systems and rapid changes in patient metabolism and acid-base balance complicate logistics for ambulation. Here we present a wearable ECCO2R system with exhaust gas CO2 (EGCO2) sensing capabilities. Methods: The wearable ECCO2R system (Fig 1) integrates a blower module, a membrane oxygenator optimized for CO2 removal (MLung), and an exhaust module. Two redundant blowers push air through a flow sensor, to maintain fixed flow rates, then through the MLung. A CO2 sensor (STC31) in the exhaust module senses MLung EGCO2. It is preceded by a water trap, sampling pump, Nafion tubing, and heater which remove moisture and protect the STC31. Pressure sensors record the gas-side pressure drop of the MLung. First, control of sweep flow and CO2 sensing were tested individually. The blower module was attached to the MLung and commanded to maintain a set of target flows. The exhaust module was directly fed compressed CO2 and N2 to ensure it could measure a range of CO2 concentrations. Finally, as a system in-vitro test (Fig 2), the device was electronically integrated and connected to a conditioning lung fed by compressed CO2 and N2. The CO2 concentration in the sweep gas of the conditioning lung was varied to simulate metabolic changes. Results: The assembled device measures 23x20x8 cm and weighs 1.4 kg (with primed MLung and tubing; without batteries). The device quickly (<2s) attained target sweep up to 4 L/min (Fig 3A), and has a maximum sweep flow of 7 L/min with the MLung. It measured EGCO2 for all values tested (Fig 3B; up to 50 mmHg; <1 mmHg error). During the system test with water, the ECCO2R system was able to qualitatively detect changes in EGCO2 caused by the simulated metabolic changes. Conclusion: We present progress toward the first wearable ECCO2R system. Its integrated CO2 sensing makes it a suitable platform for future use as the first ECCO2R with closed-loop feedback control to automatically respond to the respiratory needs of the patient.Figure 1. (A) Blower module showing internals. (B): Sensor module; most components are enclosed. (C) Rendering of system on a patient, with arteriovenous access to the subclavian a. and v.Figure 2. System-level test setup. Blue arrows denote gas flows, and red arrows denote water flows (water is used as an analog for blood). In this test, compressed CO2 was fed into the conditioning lung. The CO2 was dissolved into the circulating water, and then removed by the MLung. Finally, it went to the exhaust module.Figure 3. (A) The device quickly attains desired sweep flows. It has a 7 L/min maximum flow rate when used with the MLung. (B) With a 2-point calibration, the device accurately (<1mmHg) measures CO2 in a gas stream, in reference to an arterial-blood-gas machine.