Otteni J C, Ancellin J, Cazalaà J B
Service d'anesthésie-réanimation chirurgicale, CHU de Hautepierre, Strasbourg, France.
Ann Fr Anesth Reanim. 1997;16(1):68-72. doi: 10.1016/s0750-7658(97)84283-9.
A defective Air/O2 mixer of a ventilator located downstream of the gas outlets of two pipelines is a potential cause of retropollution. Retropollution of O2 with Air or vice versa carries a risk of either a) a hypoxic gas mixture delivery during anaesthesia, including O2-N2O administration, when the O2 pipeline supplies Air instead of O2, or b) a hyperoxic gas mixture delivery in the intensive therapy unit for neonates during administration of a O2-Air mixture, when the Air pipeline supplies O2 instead of Air. A defective O2/N2O flowmeter-mixer of an anaesthesia machine, with N2O flow control by O2 through a differential pressure manometer, can cause retropollution of O2 supply pipeline with N2O or vice versa. The prerequisite for retropollution is the association of three events: build-up of a pressure difference between the two gas lines; defective or absent back-flow check value in the circuit of the gas at a lower pressure; one of the following defects: a) the pressure equilibrating valves of the mixer cannot amend the pressure difference and allow a gas reflow at the gas mixture outlet; b) leak in the diaphragm of a pressure equilibrating valve; c) defective bypass supply valve. The optimal means for the recognition of a pipeline contamination by another gas is the O2 analyzer, especially in anaesthetic areas where the presence of N2O and Air carries the risk of a hypoxic gas mixture delivery. The mixer or flowmeter-mixer responsible for retropollution can be recognized in plunging successively the various quick couplers underwater into a glass, while the others remain connected to their outlets and the mixer set at a O2 concentration of 50 vol% or the flowmeters set at a similar flow. In case of retropollution, the gas reflow produces bubbles. It is recommended: a) in anaesthetic areas to set the O2 pressure at about 0.2 bar above that of Air and the latter at a pressure of about 0.2 bar above that of N2O; b) in intensive therapy units for neonates, to set the Air pressure at about 0.2 bar above that of O2; c) in all areas to disconnect from the gas outlets the devices equipped with a mixer or a flowmeter-mixer when not in use.
位于两条管道气体出口下游的呼吸机的空气/氧气混合器故障是逆流污染的一个潜在原因。氧气与空气的逆流污染存在以下风险：a）在麻醉期间，包括使用氧气 - 氧化亚氮时，当氧气管道供应的是空气而非氧气时，会输送低氧混合气体；b）在新生儿重症监护病房使用氧气 - 空气混合气体时，当空气管道供应的是氧气而非空气时，会输送高氧混合气体。麻醉机的氧气/氧化亚氮流量计 - 混合器故障，通过差压计由氧气控制氧化亚氮流量，可能导致氧气供应管道被氧化亚氮逆流污染，反之亦然。逆流污染的前提是三个事件同时发生：两条气体管路之间形成压差；低压气体回路中回流止回阀有缺陷或缺失；以下缺陷之一：a）混合器的压力平衡阀无法修正压差并允许气体在混合气体出口处回流；b）压力平衡阀隔膜泄漏；c）旁路供应阀故障。识别管道被另一种气体污染的最佳方法是使用氧气分析仪，特别是在存在氧化亚氮和空气且有输送低氧混合气体风险的麻醉区域。负责逆流污染的混合器或流量计 - 混合器可以通过依次将各个快速接头浸入水下的玻璃杯中进行识别，而其他接头仍连接到其出口，并且混合器设置为氧气浓度50%（体积）或流量计设置为类似流量。发生逆流污染时，气体会产生气泡。建议：a）在麻醉区域，将氧气压力设置为比空气压力高约0.2巴，空气压力设置为比氧化亚氮压力高约0.2巴；b）在新生儿重症监护病房，将空气压力设置为比氧气压力高约0.2巴；c）在所有区域，不使用时将配备混合器或流量计 - 混合器的设备从气体出口断开。
