The document discusses anaesthetic gas scavenging systems which collect excess gases from patient breathing circuits to maintain a safe operating room environment. It describes the components of effective scavenging systems including collecting waste gases, transferring them via tubing, and properly disposing of them. Both passive systems which rely on pressure flow and active systems which use suction are examined. Guidelines for monitoring scavenging system function and controlling pollution in operating rooms are also provided.

1. Scavenger system
in
OR
Dr. P K Maharana

2. Introduction
• When patients are administered anaesthetic gas, its molecules escape into the room and can impact
the performance of medical teams.
• Since the use of gases and agents exceeds the amount necessary for the patient it always escapes to
the surrounding environment and necessary to scavenge it out to keep the environment safe for others.
• Since the late 1960s there has been speculation that trace anaesthetic gases/vapours may have a
harmful effect on operating theatre personnel.
• It has been concluded from currently available studies that there is no association between
occupational exposure to trace levels of waste anaesthetic vapours in scavenged operating theatres
and adverse health effects.
• However, it is desirable to vent out the exhaled anaesthetic vapours and maintain a vapour-free theatre
environment.
• In the Operating Room the Anaesthetic Gas Scavenging System collects and removes waste gases
from the patient breathing circuit and the patient ventilation circuit.
• It can also collect any type of gases or aerosolized medications that is intended only for the patient
should not be breath by others.
• Air Liquid Healthcare provides reliable AGSS systems to ensure the safety of your patients and staff.

3. THE IDEAL SCAVENGING SYSTEM
.
• Should not affect the ventilation and oxygenation of the
patient.
• Should not affect the dynamics of the breathing system.
• A well-designed scavenging system should consist of a
collecting device for gases from the breathing
system/ventilator at the site of overflow, a ventilation system
to carry waste anaesthetic gases from the operating theatre
and a method for limiting both positive and negative pressure
variations in the breathing system.
• The performance of the scavenging system should be part of

4. Definition
An anaesthetic gas scavenging system is a system or
device that collects excess anaesthetic gas from the
breathing system and discharges it outside the
working environment.
• It is used to collect gases or aerosolized medications from the patient
exhalations or found near the patient area because of some treatment
related activities. Often associated with delivery of anaesthesia but may also
include other patient related activities .

5. Objective
 In most jurisdictions, there is a legal requirement to scavenge waste
gases to maintain the level of waste gases in the Operating Room below
the legally acceptable limit.
 In the UK: the limits are typically 100ppm for nitrous oxide and
50ppm for halogenated volatile anaesthetic agents (except halothane
which is 10ppm).
 Other jurisdictions have different requirements for local
environmental contamination
• Nitrous oxide maximum 25ppm and
• Halogenated volatile gases maximum 2ppm.
 In addition to the legal requirement there is an Occupational Health
requirement to maintain a safe workplace and limit exposure to potentially
harmful gases and agents.
 Anaesthetic gas scavenging systems prevent medical staff from
inhaling the anaesthetic nitrous oxide administered to patients

6. Recommended levels for different agents.
• In the United States, the maximum accepted concentrations
of any Halogenated agent should be less than 2 ppm.
• When such agents are used in combination with nitrous
oxide, levels of less than 0.5 ppm should be achieved.
• Nitrous oxide, (when used as the sole anaesthetic agent), at
8-hour time-weighted average concentrations should be less
than 25 ppm during the administration of an anaesthetic.
• Holland has a limit of 25 ppm for nitrous oxide, whereas Italy,
Sweden, Norway and Denmark set 100 ppm as their limit for
exposure to nitrous oxide.
• It is not possible to set uniform levels without sufficient data.

7. Level of different agents which showed no
significant adverse effects on animal studies.
• 100 particles per million (ppm) for nitrous oxide
• 50 ppm for enflurane
• 50 ppm for isoflurane
• 10 ppm for halothane
• 20 ppm for sevoflurane (recommended by Abbot Laboratories)
• No limit set for desflurane although a 50 ppm target is advisable due to
its similarity to enflurane.
 These levels were chosen because they are well below the levels at
which any significant adverse effects occurred in animals and
represent levels at which there is no evidence to suggest human health
would be affected.
 Although not universally agreed upon, the recommended maximum
accepted concentrations in the UK (issued in 1996), over an 8-hour

8. Factors responsible for theatre pollution
Anaesthesia Techniques Anaesthesia Machines
• Leaks from various
connections like tubing
connections if not fitting
properly, soda lime
canister etc.
• Others: Cryosurgery
Unit, Cardiopulmonary
bypass circuit if vapor is
Poorly fitting facemask
Pediatric breathing system( T-piece)
Un-cuffed tracheal Tubes
Gases coming out through APL valve
Gases coming through ventilator
exhaust
Exhalation gases during recovery
Spillage during filling of vaporizers

9. How to reduce pollution in OR?
 1. Adequate theatre ventilation and air conditioning, with frequent and rapid changing of the
circulating air (15–20 times per hour).
 Theatres that are unventilated are four times as contaminated with anaesthetic gases and vapours compared
to those with proper ventilation.
 A non-recirculating ventilation system is usually used. A recirculating ventilation system is not recommended.
In labour wards, where anaesthetic agents including Entonox are used, rooms should be well ventilated with
a minimum of five air changes per hour.
 2. Use of the circle breathing system.
 This system recycles the exhaled anaesthetic vapours, absorbing CO2.
 It requires a very low fresh gas flow, so reducing the amount of inhalational agents used.
 3. Total intravenous anaesthesia.
 4. Regional anaesthesia.
 5. Avoiding spillage and using fume cupboards during vaporizer filling.. Modern vaporizers use special
agent-specific filling devices as a safety feature and to reduce spillage and pollution.
 6. Scavenging.

10. Scavenging
• In any location in which inhalation anaesthetics are
administered, there should be an adequate and reliable
system for scavenging waste anaesthetic gases.
• A scavenging system is capable of collecting the waste
anaesthetic gases from the breathing system and
discarding them safely.
• Unscavenged operating theatres can show N2O levels of
400–3000 ppm.

11. The basic functional components of an Anaesthetic
Gas Scavenging System are as follows:
• 1.A collecting assembly / shroud with a relief valve by
which the waste gas leaves the breathing or ventilation
circuit.
• 2.A transfer system of tubing to conduct waste gases to
the Scavenging Interface.
• 3.The Scavenging Interface, and
• 4.A Disposal line to conduct the waste gas to a
passive evacuation system, or a Waste Anaesthetic
Gas Disposal/Medical Vacuum system via a station outlet.

12. A receiving system
• . A receiving system (reservoir bag) can be used.
• Two spring-loaded valves guard against excessive positive
(1000 Pa) in case of a distal obstruction or negative (–50 Pa)
pressures in case of increased demand in the scavenging
system.
• Without these valves, excessive positive pressure increases
the risk of barotrauma should there be an obstruction beyond
the receiving system.
• Excessive negative pressure could lead to the collapse of the
reservoir bag of the breathing system and the risk of

13. Mechanism of action
• 1. The exhaled gases are driven by either the patienťs respiratory efforts
or the ventilator.
• 2. The receiving system should be mounted on the anaesthetic machine
to minimize the length of transfer tubing, therefore minimizing resistance
to flow.
• Problems in practice and safety features
• 1. Connecting the scavenging system to the exit grille of the theatre
ventilation is possible. Recirculation or reversing of the flow is a problem
in this situation.
• 2. Excess positive or negative pressures caused by the wind at the outlet
might affect the performance and even reverse the flow.
• 3. The outlet should be fitted with a wire mesh to protect against insects.
• 4. Compressing or occluding the passive hose may lead to the escape of
gases/vapours into the operating theatre and thereby polluting it.
• The disposal hose should be made of non-compressible materials and not

14. Scavenging System(Active & Passive)
Active System
• Uses a device like
suction to draw gases
from breathing system.
• Mostly uses a
compressor to draw the
gases and agents.
• Expensive
• Requires maitenance.
Passive System
• This system uses
pressure in the gas line to
drive out the gases out of
the machine.
• It must be located
adjacent to an outside
place.
• The pipes simply passes

15. Passive System
The passive system is simple to construct with zero
running cost.
• Components
• 1. The collecting and transfer system which consists
of a shroud connected to the adjustable pressure
limiting (APL) valve (or expiratory valve of the
ventilator).
• A 30-mm connector attached to transfer tubing leads
to a receiving system.
• The 30-mm wide-bore connector is designed as a safety
measure in order to prevent accidental misconnection to

16. Schematic diagram of
scavenging system, showing
alternative types of receiving and
disposal

17. Lack Circuit(J. A. LACK)

18. Connection to be fitted to APL valve

20. F/air Canister

21. Diagram of a passive scavenging system.
Modern scavenging system has four
components.
a). Collecting System:
b).Transferring System:.
c). Receiving System:
d). Gas disposal Assembly: May be a passive
or active disposal unit.

22. Drawing showing
the flow system of
gases.

23. Active system
Components
• 1. The collecting and transfer system is similar to that of
the passive system .

24. Monitoring the functioning of Scavenging
system.
 Sampling procedures for evaluating waste anaesthetic vapour
concentrations in air should be conducted for nitrous oxide and
halogenated agents on a yearly basis in the UK and on a
quarterly basis in the USA in each location where anaesthesia
is administered.
 Monitoring should include:
• a) Leak testing of equipment
• b) Sampling air in the theatre personnel breathing zone.
Planned preventative maintenance (PPM)
programme. Anaesthetic equipment, gas scavenging, gas supply,
flowmeters and ventilation systems must be subject to a
maintenance programme.
At least once annually, the general ventilation system and the

25. Guidelines for controlling pollution in OR
• There is no association between occupational exposure
to anaesthetic agents trace levels and adverse health
effects.
• There are no agreed international standards of the
maximum accepted concentrations of agents in the
theatre environment.
• Routine monitoring and testing (PPM) are mandatory.

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