“The signs of oxygen want and plane of anesthesia as shown by color, muscular phenomena, etc. must be watched constantly…”

Ralph Waters, MD, Anesthesia & Analgesia, 1926

One hundred years ago, Dr. Ralph Waters introduced carbon dioxide absorbents to facilitate rebreathing of exhaled anesthetics, and reduce the need for adding fresh gas and anesthetic to the breathing circuit. Advantages included reduced use (cost) of inhaled anesthetics, reduced exposure of the surgical team to anesthetics, since scavenging systems were not used, and better preservation of the patient’s temperature and airway humidity. As the quote above from his 1926 article indicates, Dr. Waters was concerned about the safety implications of reducing fresh gas flow, specifically inadequate oxygen and inadequate anesthetic depth (Anesth Analg 1926;5:160-2). With careful clinical observation, Dr. Waters was able to safely practice low-flow anesthesia using a bag-mask type device with an integrated CO2 absorbent. In 1936, he published his experiences of using this technique to safely administer 20,000 anesthetics over more than 15 years. (Proc R Soc Med 1936;30:11-22). This is indeed a remarkable achievement considering that monitoring the adequacy of oxygen and anesthetic concentrations relied upon clinical observation alone.

Fast forward 100 years, and the practice of low-flow anesthesia is in the spotlight. While the advantages of reducing cost and preserving heat and humidity are still relevant, global warming has highlighted the environmental impact of inhaled anesthetics, adding another motivation to adopt practices that reduce the anesthetic gases entering the atmosphere via the scavenging system. The safety concerns remain unchanged. Reducing fresh gas flow to create rebreathing of exhaled gas increases the risk of inadequate oxygen and anesthetic delivery. While Dr. Waters only had his skills of clinical observation to keep his patients safe, in modern anesthesia practice we have the technology to continuously monitor oxygen and anesthetic concentrations, as well as blood oxygenation (pulse oximetry) and the patient’s anesthetic depth (processed EEG). While there are additional technologies to help the anesthesia professional safely reduce fresh gas flow, knowledge of the impact of reducing fresh gas flow is required to become skilled at the art of low-flow anesthesia. Significantly reducing inhaled anesthetic pollution requires practice strategies during all phases of the anesthetic – induction, maintenance, and emergence.

The scientific foundations of low-flow anesthesia have been well known for decades and readily available in both journal and textbook publications. Many of the publications are highly technical, however, and the basic knowledge needed to practice low-flow anesthesia has not been consistently taught to trainees, nor does board certification require any specific knowledge of the practice. Fortunately, the Anesthesia Patient Safety Foundation (APSF), in collaboration with ASA, has launched an online course on low-flow anesthesia using guided simulation to help the learner develop the mental models needed to comfortably embark on a practice of low-flow anesthesia. (Figure) The course is free to all anesthesia professionals and offers continuing education credits as well.

Figure: Guided, simulation-based course on low-flow anesthesia with visualization of gas flows. Example indicates how reducing fresh gas flow (FGF) causes rebreathing and reduced waste out the scavenging system. FD, FI, and FE refer to fractions of oxygen (O2) and anesthetic agent (A) in the delivered, inspired, and expired gases, respectively.

Figure: Guided, simulation-based course on low-flow anesthesia with visualization of gas flows. Example indicates how reducing fresh gas flow (FGF) causes rebreathing and reduced waste out the scavenging system. FD, FI, and FE refer to fractions of oxygen (O2) and anesthetic agent (A) in the delivered, inspired, and expired gases, respectively.

The course is divided into eight topics, each intended to require about a 15-minute interaction to complete. Three credit hours are offered for CME since the simulation can be used to explore practices beyond the guided topics, and other resources are available to learn about the practice of low-flow anesthesia. Fundamental topics of low-flow anesthesia are taught along with clinical strategies for reducing fresh gas flow during maintenance, induction, and emergence. Since CO2 absorption is essential to the practice of low-flow anesthesia, there is a specific topic on CO2 absorbents, including a discussion of why sevoflurane can be used safely and effectively at fresh gas flow settings well below those described in the drug labeling. (Please see the online article for additional details about the course and other low-flow information.)

It is remarkable that Ralph Waters was able to practice low-flow anesthesia using just a bag and mask, and his clinical skills. In modern practice, every anesthetizing location where a circle system is used to administer an inhaled anesthetic has capabilities to support the safe practice of low-flow anesthesia that far exceed what was available to Dr. Waters. The road to reducing fresh gas flow and the cost and environmental impact of your inhaled anesthetic practice is a short course away. It is available online, free to all with continuing education credits for all professionals. For physicians enrolled in the MOCA process, the CME credits are safety eligible. Why wait? Follow the link to the APSF Low-Flow Anesthesia landing page (apsf.org/tei/lfa).