These systems connect the exhaust of the breathing system to the hospital vacuum system via an interface controlled by a needle valve.
The Ohio scavenging interface has connections for the outlets from the breathing system and ventilator (A), one or two reservoir bags (B) and the vacuum line (V). The suction is controlled by the needle valve (N). There are both positive (P1) and negative (P2) pressure relief valves in case the reservoir bag becomes empty or too full.
An example of a simple scavenging system:
This consists of a reservoir made of plastic pipe of around 3" in diameter and 2 feet in length, capped at both ends and with a needle valve fitted at the bottom. Two holes are drilled in the top cap, one to allow the hose from the outlet of the anaesthetic machine to be inserted and the other to allow passage of atmospheric air. The valve is adjusted so that air is slowly sucked into the pipe when the anaesthetic machine is in use: this will prevent waste gases escaping into the atmosphere.
Convenient in large hospitals, where many machines are in use in different locations
Vacuum system and pipe work is a major expense
Needle valve may need continual adjustment