What is scavenging in OT? what are five basic parts of a scavenging system? What are the hazards of a scavenging system?
Scavenging is the collection and the subsequent removal of waste
anesthetic gases from the operating room
Scavenging systems generally have five components (1) the gas-collecting assembly, (2) the transfer means, (3) the
scavenging interface, (4) the gas-disposal assembly tubing, and (5) an active or
passive gas-disposal assembly An “active
system” uses a central evacuation system to eliminate waste gases. The “weight”
or pressure of the waste gas itself produces flow through a “passive system.
”
Gas-Collecting Assembly
The gas-collecting assembly captures excess anesthetic gas and
delivers it to the transfer tubing. Waste
anesthetic gases are vented from the anesthesia system either through the APL
valve or through the ventilator relief valve which accumulates in the gas-collecting assembly and is directed to the
transfer means.
Transfer Means
The transfer means carries excess gas from the gas-collecting
assembly to the scavenging interface. The tubing must be either 19 or 30 mm, and should be sufficiently rigid to prevent kinking, and as short as possible
to minimize the chance of occlusion.and is sometimes color code with yellow to distinguish it from 22-mm breathing system tubing.. The two tubes frequently merge into a single hose
before they enter the scavenging interface.
Scavenging Interface
The scavenging interface is the most important component of the
system because it protects the breathing circuit or ventilator from excessive
positive or negative pressure. The interface
should limit the pressures immediately downstream from the gas-collecting
assembly to between -0.5 and +10 cm water with normal working conditions. Interfaces can be open or closed, depending on the
method used to provide positive and negative pressure relief.
Open Interfaces
An open interface contains no valves and is open to the atmosphere,
allowing both positive and negative pressure relief. Open interfaces is used with active disposal systems that use a central evacuation system.
Open interfaces require a reservoir because waste gases are intermittently
discharged in surges, whereas flow from the evacuation system is
continuous.
An open canister provides reservoir capacity which should be large enough to accommodate a variety of waste gas
flow rates. Gas enters the system at the top of the canister and travels through
a narrow inner tube to the canister base. Gases are stored in the reservoir
between breaths. Positive and negative pressure relief is provided by holes in
the top of the canister
Closed Interfaces
A closed interface communicates with the atmosphere through valves.
All closed interfaces must have a positive-pressure relief valve to vent excess
system pressure if obstruction occurs downstream from the interface. A
negative-pressure relief valve is mandatory to protect the breathing system from
subatmospheric pressure if an active disposal system is used. Two types of closed interfaces are commercially
available. One has positive pressure relief only; the other has both positive
and negative pressure relief.
Gas-Disposal Assembly Conduit
The gas-disposal assembly conduit conducts waste gas from the scavenging interface to the
gas-disposal assembly. It should be collapse-proof and should run overhead, if
possible, to minimize the chances of accidental occlusion
Gas-Disposal Assembly
The gas-disposal assembly ultimately eliminates excess waste gas There are two types of disposal systems:
active and passive.
The most common method of gas disposal is the active assembly,
which uses a central evacuation system. A vacuum pump serves as the mechanical
flow-inducing device that removes the waste gases usually to the outside of the
building.
interface with a negative-pressure relief valve is
mandatory because the pressure within the system is negative. A reservoir is
very desirable, and the larger the reservoir, the lower the suction flow rate
needed.
Hazards
Scavenging systems add
complexity to the anesthesia system.
A scavenging system extends
the anesthesia circuit all the way from the anesthesia machine to the ultimate
disposal site.
Obstruction
of scavenging pathways cause excessive positive pressure in the breathing
circuit, resulting in barotrauma .
Excessive vacuum to a scavenging
system can cause undesirable negative pressures within the breathing system.
Scavenging system catching fires in engineering equipment rooms that house the
vacuum pumps used for waste anesthetic gas evacuation. due to oxygen enrichment
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