What is scavenging?
- collection of excess gases from equipment used in administering anesthesia, or exhaled by patients
- removal of these excess gases to an appropriate place of discharge outside the working environment
How does a scavenger decide what remove?
- the scavenger maintains constant pressure in breathing circuit
- removed FGF - volume lost in patient’s O2 consumption
What is the OSHA recommended Level for volatile halogenated anesthetic alone?
2ppm
What is the OSHA recommended Level for nitrous oxide alone?
25 ppm
What is the OSHA recommended Level for volatile halogenated anesthetic with nitrous oxide?
Less than or equal to 0.5 ppm and 25ppm respectively
How does nitrous oxide affect the concentration of an anesthetic in the blood stream?
- second gas effect
- small molecule
- increase soluability coeffient
- higher saturation
What are determinants of exposure to waste gases
- amount of OR ventilation and air turnover
- functional status of anesthesia equipment (machine check/circuit check)
- good fitting mask
- present FGF from entering atmosphere
- turn off anesthetic gas before suctioning patient
- evacuate anesthetic gases into scavenger at end of case
- cuffed/uncuffed ETT (uncuffed lets air escape up)
- integrity of equipment (leaks present)
- TIVA
- avoid N2O
- high FGF can flush more volume into air
What are the five basic components of a scavenging system
- gas collection assembly
- transfer means
- scavenging interface
- gas disposal tubing
- gas disposal assembly
Describe the Gas collection Assembly
- output usually 30mm male-fitting connection
- captures excess gases at the site of emission (breathing)
- site include: APL valve during spontaneous ventilation, spill valve in mechanical ventilation
- delivers the gas to the transfer means tubing
Describe the Transfer Means tubing
- aka exhaust tubing or hose and transfer system
- conveys ga to collection assembly to interface
- usually a made of short, fat (large diameter) tubing with female connector
- designed to carry high flow without increase in pressure
- yellow color; stiffer plastic than breathing tube
Describe the Scavenging Interface
- aka balancing device and balancing valve
- most critical component of the scavenging system
- 30mm male connector
- should be situated as close as possible to the gas-collecting assembly
- 2 types (open/closed)
- 3 elements (positive pressure relief, negative pressure relief, and reservoir capacity)
- prevents pressure increases and decreases to be transmitted to breathing system
What happens when the scavenger removes too much gas from the system?
- creates a negative pressure system or a vacuum in the circuit
What happens when the scavenger does not remove enough gas from the system
- there is too much pressure in the system and could lead to barotrauma
What is an open scavenging interface
- this means it is “open” to the atmosphere via “relief ports” in reservoir, avoiding buildup of positive or negative pressure
- removes risk of barotrauma or vacuum creation in breathing circuit
- utilizes reservoir (open canister) and central vacuum (literally vacuum)
- gas enters the system at the top of the canister and travels through a narrow inner tube to the base
- vacuum control valve can be adjusted to the level of suction on the canister/reservoir (must be equal to or greater than the excess gas flow rate to prevent OR pollution)
In an open system too much suction from the vacuum results in what?
Entrains room air into scavenger
In an open system too little suction from the vacuum results in what?
Scavenged gas into the OR
What is a closed system interface?
-
Two types:
- positive pressure relief only
-negative pressure relief and positive pressure relief
Closed System with positive pressure relief only
- single positive: pressure relief valve opens when a max pressure is reached
- passive disposal: no vacuum used; no reservoir bag needed
Closed System with positive and negative pressure relief
- has positive pressure relief valve, and negative pressure relief valve and a reservoir bag
- used with an active disposal system (vacuum control valve adjusted two that the reservoir bag is not over distended or completely deflated)
- gas is vented to the atmosphere if the system pressure exceeds 5cm H2O
- room air is entrained if the system pressure is less than -0.5cm H2O
- a backup negative pressure relief valve opens at -1.8cm H2O if the primary negative pressure relief valve becomes occluded
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