title: [Definition of a leak model and derivation of formulas for quantifying the accompanying leak surfaces in the anesthetic system].
abstract: Our intention was to conceive a simple model for the evaluation of well-defined leakages in the anesthetic breathing system. Utilization of any model requires a formula to calculate the corresponding leakage surfaces. METHOD. The leak is defined as the projection of a circle (radius r) onto the surface of a cylinder (radius R) in which anesthetic gas is flowing. If we remove the leakage surface from the cylinder and flatten it out this produces neither a circular nor an elliptic shape. We will develop an expression for the leakage surface depending on the two radii, r and R, in a two-dimensional coordinate system. RESULTS. Formulas (3), (4) and (5) can be used to compute leakage areas for our model. An analytic solution of the equations is impossible by the application of calculus, but a PC program for numeric integration can yield values with a sufficient degree of accuracy. Some results for well-defined leakages in breathing tubes (R = 11 mm) are shown. These show that the difference between the leakage area and the projected circle (radius r) can practically be neglected for some values of r. CONCLUSION. Leakages in most anesthetic breathing systems cause some gas loss. The main causes are leaking plug connections and screw joints. Damage to the breathing tubes or bellows is less significant. Part of the tidal volume will disperse into the environment via the leak. This might be hazardous for the patient because the breathing volume and inspiratory oxygen concentration are reduced and for the operating team because of air pollution. To examine how such parameters as flow, compliance and resistance cause loss of pressure and volume and variations in gas concentration in the case of leakages an appropriate model of practical use is needed. Application of the formulas derived from our model makes it possible to compare measurements gained from studying the impacts of leakages in cylindrical tubes of different diameters. By experimental research of pressure and volume loss we intend to gather reliable information that will allow us to make proper recommendations for efficient setting of the pressure disconnection alarm.
authors.affiliation: Institut für Anaesthesiologie, Universität Erlangen-Nürnberg.
authors.forename: U
authors.initials: U
authors.lastname: von Hintzenstern
authors.forename: G
authors.initials: G
authors.lastname: Berthold
authors.forename: S
authors.initials: S
authors.lastname: Daun
authors.forename: G
authors.initials: G
authors.lastname: Bäz
mesh_terms: D000769:Anesthesia, Inhalation / Q000295:instrumentation*; D004868:Equipment Failure; D006801:Humans
vernacular_title: Definition eines Leckagemodells und Herleitung von Formeln zur Quantifizierung der zugehörigen Leckflächen im Narkosesystem.