Inhalation Anesthesia Kinetics

The kinetics of inhaled anesthetics is fundamental to the clinical practice of anesthesia. It explains the time course of anesthetic movement from the vaporizer and flow meters to the patient’s brain. In 1950 and 1951, Kety wrote a pair of seminal articles on this subject, one for anesthesiologists1 and one for mathematicians2. Interest in those articles led Edmund I Eger II to direct his career toward verifying and extending Kety’s thinking and teaching3 to the unified and apparently complete science we call “uptake and distribution” or “pharmacokinetics” of inhaled gases and vapors. Following Kety’s approach, the measure of anesthetic in each location is anesthetic tension. In equilibrium, anesthetic tension in all connected compartments is equal. At the same time, anesthetic concentrations in compartments differ according to drug solubility in each compartment. This text, modified from my section of the Atlas of Clinical Anesthesiology, follows Kety’s development and explains the subject using a set of figures created with the computer simulation I created for this purpose, Gas Man5. Some of these figures have been directly simulated in Gas Man for Macintosh6, extracted, and annotated while others have been copied directly from pictures, graphs, and overlays from Gas Man Version 2 for Windows7 or Version 3.1.8 for Windows 95, 98, NT, XP, Macintosh with OS 9 or OS X in a Classic window8. Gas Man is introduced in Figures 3 and 4.