Using the Anesthetic Gas Filter CONTRAfluran While on Cardiopulmonary Bypass: Preliminary Study of the Feasibility, Security, and Efficiency

The two hypnotic agents currently used for the maintenance of general anesthesia during cardio-pulmonary bypass (CPB) are propofol and sevoflurane. Propofol can be administered directly in the cardiotome of the CPB while sevoflurane is administered through the CPB's oxygenator1. Both agents have environmental concerns, and, as far as we know, the carbon footprint of those two agents are equivalent2. But, to do so, anesthesiologists have to be very cautious when using sevoflurane. One of the main issues is to maintain a fresh gas flow ≤0.5 liter per minute2. This condition cannot be met while on CPB. To insure a good gas exchange, the gas flow through the CPB oxygenator should be approximately equal to the CPB output (2.4 L min−1m−2 for an adult patient under normothermic conditions). CONTRAfluran © (ZeoSys Medical Gmbh, Luckenwalde, Allemagne) is a gas capture system: it contains a unique adsorbent that captures 99% of the sevoflurane or desflurane contained in the exhaled gases. It has been developed to prevent the release of these volatile anesthetic gases into the operating room and atmosphere. It is of particular interest because the gas captured by the device can be extracted, retreated and, potentially re-used (pending a regulatory and legal approval)3. It consists in a canister to capture the anesthetic gases and a sensor (SENSOfluran© ZeoSys Medical Gmbh, Luckenwalde, Allemagne) indicating when the canister is saturated. In a global approach to reduce our environmental impact we wanted to test the possibility of adapting a CONTRAfluran© device on the outlet of a CPB oxygenator and to evaluate the safety and the efficiency of the installation. For ethical and economical reasons, we conducted this pilot study on a bench to test the oxygenation, decarboxylation and safety of the CPB circuit we use on a daily basis equipped with a CONTRAfluran© device (figure 1), trying to mimic as closely as possible our clinical practice. The circuit was tested using all the theorical flow of our oxygenator (Inspire 8F SORIN ©, suitable for a blood flow from 4 to 8 L min−1). The CPB priming solution were composed with Ringer lactate and whole blood of a pig (which had been euthanised after another experiment and approval of ethics committee) (total volume: 500 mL, final hemoglobin level: 6 g dL−1). Sevoflurane was directly administered into the gas inflow of the oxygenator via a calibrated anesthesia vaporizer (G.E Datex Ohmeda Tec 7© Soma Tech Intl, Bloomfield, USA). The inspired fraction of sevoflurane varied between 1 and 3%, according to our clinical practice. We conceived, with a 3D printer, a device to adapt the 30 mm hose to the 6.35 mm (1/4 inch) gas outlet of the oxygenator (see 3D printed adapter in Supplementary Material). We added a water trap to avoid water condensation and saturation in the hose and in the CONTRAfluran© with water. Indeed, the temperature drop from the oxygenator (36°C) to the room temperature (19°C) caused condensation of the gas mixture saturated with water vapor (figure 2) The oxygenation capacity was tested by measuring the rise of the oxygen partial pressure (PO2) when the FiO2 of the gas mixture entering the oxygenator was increased. The decarboxylation capacity was tested by measuring the drop in the carbon-dioxide (CO2) partial pressure (PCO2) when the inspired fraction of CO2 of the gas mixture entering the oxygenator was decreased. To verify if the CONTRAfluran© did not produce an increase in CPB circuit pressure, the pressures were measured on two different points in the circuit (Figure 1: number 8 and 11) during all the experiments. We also disconnected our installation periodically to see if the manipulation had any impact on these pressures. We monitored the amount of gas bubbles present in the circuit with two gas embolus detector (figure 1: number 12 and 13). To test the efficiency of the device, we measured the sevoflurane with our anesthetic workstation (G.E Aisys CS²©) anesthetic gases monitoring system (figure 1: number 27) at three different points of the circuit: at the entry of the oxygenator (aSEVO), at the outlet of the oxygenator (sevoflurane received by the CONTRAfluran©) and at the outlet of the CONTRAfluran© device (Sevo out). In addition, the experiments were repeated 3 times with the same canister to ensure that our results were not dependent on the canister's saturation in volatile anesthetics. Once with a new canister, once with a used canister but without any saturation warning and finally with a saturated canister (red light flashing and alarming) (see Supplementary Material for the experimental plan). During these 3 experimental setting (with a new canister, with a used canister and with a saturated canister), oxygenation and decarboxylation were maintained, no presence of bubbles were detected, and the circuit pressures were not affected by the addition of the CONTRAFluran© device. From an efficiency point of view, the CONTRAFluran© scavenged all the sevoflurane from the oxygenator gas outlet, over the entire range of blood flow (from 4 to 8 L min−1) and of sevoflurane administration (from 1 to 3% of the administered gas) (see Supplementary Material for the detailed results). These results show that the CONTRAFluran© device effectively scavenges the volatile anesthetics at the outlet of the oxygenator of a CPB circuit: given the fresh gas flows used during CPB, this could result is significant decrease in the release of anesthetic gases in the atmosphere. These results need to be confirmed with a study on an animal model before testing in humans. 1McMullan V, Alston R, Tyrrell J. Volatile anaesthesia during cardiopulmonary bypass. Perfusion. 2015;30(1):6-16. doi:10.1177/02676591145313142Pauchard JC, Hafiani EM, Bonnet L, et al. Guidelines for reducing the environmental impact of general anaesthesia. Anaesth Crit Care Pain Med. 2023;42(5):101291. doi:10.1016/j.accpm.2023.1012913Hinterberg J, Beffart T, Gabriel A, et al. Efficiency of inhaled anaesthetic recapture in clinical practice. Br J Anaesth. 2022;129(4):e79-e81. doi:10.1016/j.bja.2022.04.009 The authors do not have any conflicts of interest in relation with this report. Departmental resources only.