CO2 absorption in anesthesia

Maintenance of anesthesia is mainly achieved by using inhaled anesthetics. To deliver these anesthetic gases, complex anesthesia delivery machines have been developed. An important principle is that delivery of these inhaled anesthetics is based on a continuous flow of fresh gas (composed of a mixture of air and oxygen). The reduction of these fresh gas flows is considered an important focus to further improve and optimize anesthesia delivery and practice in general. By reducing fresh gas flows, anesthesiologists try to minimize waste of these inhaled agents, thereby decreasing costs and pollution, both of the operating room and the environment (inhaled agents are greenhouse gases). Lowering fresh gas flows has an important impact on the pharmacokinetics of anesthetic gases and belongs to the essence of state-of-the art anesthesia practice. However, by lowering fresh gas flow well below minute ventilation, part of the gas that is exhaled by the patient is being re-inhaled (rebreathed). Therefore, the percentage of oxygen in inhaled gas should be higher to avoid hypoxemia. In addition, since the patient should not be rebreathing his/her own CO2 present in the exhaled gas, it passes through a CO2 absorbent before being re-inhaled. Currently used calcium hydroxide-based CO2 absorbents are safe over the entire range of fresh gas flows, but still have some shortcomings. Their production and disposal are environmentally unfriendly, they need to be refilled or replaced frequently and anesthesia providers rarely use them to full capacity. Moreover, the dust they generate, even though innocuous to the patient, may accumulate in sensitive parts of the anesthesia machine. In search of innovative technologies that address these issues, this research project will focus on a new CO2 removal device developed by DMF Medical (Halifax, Canada). It uses a technology similar to that of oxygenator membranes in cardiopulmonary bypass machines. A sweep gas is directed through the lumen of semipermeable hollow fibers, while gases from the anesthesia breathing circuit flow between the fibers. Gas exchange occurs across the semipermeable membrane of the fiber walls and permits CO2 removal while retaining (most of) the potent inhaled agent in the anesthetic gas mixture. The aim of this project is to study CO2 and inhaled agent kinetics by testing the device in vitro and in vivo. This will give more insight on the conduct of these gases in closed circuit systems in general and permits further investigation of the feasibility to use new CO2 removal devices in clinical practice. Another aim will be the investigation of the environmental and economic impact and, without doubt, its safety when used in routine clinical practice with modern anesthesia machines.