Kleemann P P
Department of Anaesthesiology, Johannes Gutenberg University Medical School, Mainz, Germany.
Anaesth Intensive Care. 1994 Aug;22(4):396-408. doi: 10.1177/0310057X9402200414.
It has been demonstrated in an experimental study in swine using the scanning electron microscope that a rebreathing technique utilising minimal fresh gas flowrates significantly improves climatization of anaesthetic gases. Consequently, effects of various anaesthetic techniques on airway climate must be assessed, which covers the need for suitable measuring devices. Basic principles and methods of humidity measurement in flowing anaesthetic gases include gravimetric hygrometry, dew point hygrometry, wet-dry bulb psychrometry, mass spectrometry, spectroscopic hygrometry and electrical hygrometry. A custom-made apparatus for continuous measurement of humidity and temperature in the inspired and expired gas mixtures of a breathing circuit (separated by a valve system, integrated between the endotracheal tube and the Y-piece) is described. Comparative evaluation of this apparatus and the psychrometer was carried out. It could be demonstrated that the apparatus, measuring with capacitive humidity sensors, is more suitable for prolonged use under clinical conditions than the psychrometer. In the second part of the study, climatization of anaesthetic gases under clinical conditions was investigated using fresh gas flowrates of 0.6, 1.5, 3.0 and 6.0 l/min. In the inspiratory limb of the circuit an absolute humidity of 21.3 mg H2O/l and a temperature of 31.5 degrees C were obtained after 120 minutes of minimal flow. Humidity and temperature of inspired air obtained with fresh gas flowrates of 6.0 and 3.0 l/min were found to be inadequate for prolonged anaesthesia. Reducing the fresh gas flow to 1.5 l/min increases heat and moisture content in the respired gases, but conditions are still inadequate for prolonged anaesthesia. Sufficient moisture (> or 20 mg H2O/l) and temperature are obtained under minimal flow conditions after one hour.
在一项使用扫描电子显微镜对猪进行的实验研究中已证明，利用最小新鲜气体流量的再呼吸技术可显著改善麻醉气体的气候化。因此，必须评估各种麻醉技术对气道气候的影响，这就需要合适的测量装置。流动麻醉气体湿度测量的基本原理和方法包括重量湿度测定法、露点湿度测定法、干湿球湿度测定法、质谱分析法、光谱湿度测定法和电湿度测定法。本文描述了一种定制装置，用于连续测量呼吸回路（由阀系统分隔，集成在气管内导管和Y形接头之间）中吸入和呼出气体混合物的湿度和温度。对该装置和干湿球湿度计进行了比较评估。结果表明，使用电容式湿度传感器进行测量的该装置比干湿球湿度计更适合在临床条件下长期使用。在研究的第二部分，使用0.6、1.5、3.0和6.0升/分钟的新鲜气体流量，对临床条件下麻醉气体的气候化进行了研究。在最小流量120分钟后，回路吸气支的绝对湿度为21.3毫克水/升，温度为31.5摄氏度。发现新鲜气体流量为6.0和3.0升/分钟时获得的吸入空气湿度和温度不足以进行长时间麻醉。将新鲜气体流量降至1.5升/分钟可增加呼出气体中的热量和水分含量，但条件仍不足以进行长时间麻醉。在最小流量条件下一小时后可获得足够的湿度（≥20毫克水/升）和温度。
