Let’s say you are performing an anesthetic. You have the fresh gas flow (FGF) at 2 L/min. We know that the FGF enters the circle circuit, joining the exhaled gas that will be rebreathed. But eventually, what happens to all the gas and vapor we control with our flowmeters and vaporizers? It has to go someplace. It has to leave the machine; otherwise, the machine would explode.
There is an exhaust for the machine. It is called the scavenger system. But it is more than merely the tail pipe for the anesthesia machine. It has a role in protecting you and the rest of the people in the OR. This assembly takes all the gas that leaves the machine and directs it out of the operating room (OR) so we are not exposed to the waste anesthetics. A properly adjusted scavenger system’s output is the same as the FGF.
There are two main types of scavenger systems, classified by whether medical suction is used to evacuate the exhaust gas. An active system requires wall or pipeline suction to evacuate the waste gas. A passive system relies on the upstream flow of gas coming out of the machine to passively flow out of the system, similar to how water flows through and out of a garden hose (a garden hose doesn’t need suction at the end of it to pull the water out of it).
As stated, an active system must be attached to some form of suction or evacuation unit, which would be the facility wall or pipeline suction. In most instances, there are separate plug-ins on the wall for scavenging suction and patient suction. Somewhere in the scavenger apparatus, there will be a means of adjusting the negative pressure from the wall, so the suction will not be too strong or too weak to be effective.
Active systems need some form of negative pressure relief to ensure the suction will not be so strong as to create a vacuum within the anesthesia machine itself. An active system also needs some type of positive pressure relief in case suction is not adequate or is disrupted so positive pressure will not build up in the anesthesia machine. In fact, one of the possible hazards of scavenger systems is barotrauma to the patient if the scavenger suction is not strong enough or is not working at all.
A passive system is a low-pressure system that relies on the passive flow of gas out of the machine and is connected to some sort of egress out of the room so as to not pollute the OR (which is, remember, the whole ...