von Hintzenstern U, Berthold G, Daun S, Bäz G
Institut für Anaesthesiologie, Universität Erlangen-Nürnberg.
Anaesthesist. 1991 Feb;40(2):113-7.
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.
我们的目的是构思一个简单的模型，用于评估麻醉呼吸系统中明确界定的泄漏情况。任何模型的应用都需要一个公式来计算相应的泄漏面积。方法。泄漏被定义为一个圆（半径为r）在麻醉气体流动的圆柱体（半径为R）表面上的投影。如果我们从圆柱体上移除泄漏表面并将其展平，它既不是圆形也不是椭圆形。我们将在二维坐标系中推导一个取决于两个半径r和R的泄漏表面表达式。结果。公式（3）、（4）和（5）可用于计算我们模型的泄漏面积。通过微积分应用无法得到这些方程的解析解，但一个用于数值积分的计算机程序可以产生具有足够精度的值。展示了一些呼吸管（R = 11毫米）中明确界定的泄漏的结果。这些结果表明，对于某些r值，泄漏面积与投影圆（半径为r）之间的差异实际上可以忽略不计。结论。大多数麻醉呼吸系统中的泄漏会导致一些气体损失。主要原因是插头连接和螺纹接头泄漏。呼吸管或波纹管的损坏不太严重。潮气量的一部分将通过泄漏扩散到环境中。这对患者可能是危险的，因为呼吸量和吸入氧浓度会降低，对手术团队也有危险，因为会造成空气污染。为了研究诸如流量、顺应性和阻力等参数在泄漏情况下如何导致压力和体积损失以及气体浓度变化，需要一个实际可用的合适模型。应用从我们的模型推导出来的公式，可以比较从研究不同直径圆柱管中泄漏影响所获得的测量结果。通过对压力和体积损失的实验研究，我们打算收集可靠的信息，以便能够为压力断开警报的有效设置提出适当建议。
