3.5 Scavenging Systems:
3.5.1 Function and characteristics:
Scavenging is the collection and subsequent removal of vented gases from the operating room. The excess gas comes from either the APL valve if the bag/vent selector switch is set to bag or from the ventilator relief valve if the bag/vent selector switch is set to "vent" All excess gas from the patient exits the breathing system through these valves. In addition, when the bag/vent selector switch is set to vent, some anesthetic breathing systems direct the drive gas inside the bellows canister to the scavenging system. The amount of delivered gas used to anesthetize a patient commonly far exceeds the patient’s needs. The anesthetist must be certain that the scavenging system is operational and adjusted properly to ensure adequate scavenging.
- Scavenging systems may be characterized as active or passive. An active system is connected to the hospital’s vacuum system and gases are drawn from the machine by a vacuum. A passive system is connected to the hospital’s ventilation duct and waste gases flow out of the machine on their own. Many anesthesia machines provide scavenging with a waste gas receiver mounted on the side of the anesthesia machine. Advantages of this system include (1) a needle valve that allows the clinician to manually adjust the amount of vacuum flow through the scavenging system, (2) a needle valve that can be adjusted such that the 3-L reservoir bag will be slightly inflated and appear to breathe with the patient, and (3) unlike other active scavenging systems, a waste gas receiver that does not require a strong vacuum to operate. If an active system is being used make sure that it is working appropriately and no occlusions are present.
3.5.2 Hazards of scavenging systems include:
- Obstruction of the scavenging pathways, which can result in excessive positive pressure in the breathing circuit and possible barotrauma.
- Excessive vacuum applied to the scavenging system, which can cause negative pressures in the breathing system.