“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...

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