Scavenging system in operating room

1. Presentor : Dr.T.Kumar
Moderator : Dr.Venkatesh
(Asst. professor)
SCAVENGING SYSTEM

2. INTRODUCTION :
Trace level - conc of anesthetic gas that is far below the one
that is needed for clinical anesthesia.
Varies greatly – depending on FGF, ventilation system , the
length of time of anesthesia, measurement site and other
variables
Degree of pollution is more during paediatric surgeries

3. Workplace exposures :
- Hospital-based and stand-alone operating rooms,
- Recovery rooms,
- Dental operatories,
- Veterinary facilities .

4. Two different classes of
chemicals:
nitrous oxide and halogenated
agents
In 1977 National Institute for
Occupational Safety and Health
(NIOSH) –
recommended exposure limits
(RELs) for both nitrous oxide and
halogenated agent

5. Methods of studies
Animal Investigations
Human Volunteer studies
Epidemiological studies of exposed humans
Mortality studies

6. Problems
Spontaneous abortions :
Epidemiological studies - Higher rates in OR personnel
than in women in other settings.
study by Viera et al. (1980), spontaneous abortion was
observed in rats at 1000 ppm or more of N2O
In summary with possible exception of N2O the conc of
halogenated agents should be some 100 times more than
what is present usually

7. Infertility : Studies found higher than expected rates of
involuntary infertility among exposed
Birth Defects : Studies show that conc of inhalation agents
are well above those found in even unscavenged OR
Impaired Skilled performance : many studies failed to
establish , but one study showed that neuropsychological
symptoms and tiredness were reported more by individuals
in OR that are less scavenged

8. Carcinogenicity : A large study found higher risk of cancer in
females than males who are exposed, but data has been
questioned.
Liver disease : recurrent hepatitis – halothane reported in
few individuals
Renal Disease
Hematological : N2O Inactivates Vit B12 – impaired DNA
sysnthesis
Cardiac Disease : higher Freq of HTN and dysrthythmias

9. Scavenging and Waste Anesthetic
Gases (WAGs)
SCAVENGING
Definition
 Scavenging is the collection and
removal of vented anesthetic gases
from the OR.
 Since the amount of anesthetic gas
supplied usually far exceeds the
amount necessary for the patient, OR
pollution is decreased by scavenging.
Scavenger and operating room
ventilation efficiency are the two
most important factors in reduction of
waste anesthetic gases (WAGs).

10. The use of scavenging devices with anesthesia delivery systems is the
most effective way to decrease waste anesthetic gases.
 An efficient scavenging system is capable of reducing ambient
concentrations of waste gases by up to 90%.
 Anesthesia machines and breathing systems delivering
halogenated hydrocarbon anesthetics and/or nitrous
oxide should not be operated unless they are equipped
with a functional scavenging system.
To be effective, a scavenging system must not leak and must control
the concentration of trace anesthetics in ambient air.
 Waste gases should not be discharged into the outside air in an area
where reentry into the building is likely.

11. Types
Scavenging may be active (suction applied) or passive (waste gases proceed
passively down corrugated tubing through the room ventilation exhaust
grill of the OR).
 Active systems require a means to protect the patient's airway from the
application of suction, or buildup of positive pressure.
 Passive systems require that the patient be protected from positive
pressure buildup only.

12. The 2 major causes of waste gas contamination in the O.R :
1. The anesthetic technique used and
2. The equipment issues
Regarding anesthesia technique the following will increase anesthetic gas
pollution when inhalant anesthetics are used:
Administering inhalant anesthetics by open drop (eg, periodically
dripping liquid volatile anesthetic onto a gauze sponge) or insufflation
(eg, delivery of a relatively high flow of anesthetic in oxygen into the
trachea or pharynx through a catheter) techniques.
Turning on flowmeters and vaporizers before attaching the breathing
system to the patient.
Allowing flowmeters and vaporizers to remain on after the patient is
disconnected from the breathing system.

13. Using uncuffed endotracheal tubes that do not create a completely
sealed airway or using cuffed tubes without inflating the cuff.
Disconnecting a patient from a breathing system without eliminating as
much of the residual gases as reasonably possible through the scavenging
system .
Spilling liquid anesthetic during the filling of vaporizers, especially
during an anesthetic procedure.
Poorly fitting masks.
Flushing the circuit.
Use of breathing circuits that are difficult to scavenge, such as Jackson-
Rees.

14. NIOSH recommendations for trace gas levels
anesthetic gas Max. TWA conc.[ppm]
Halogenated agent alone 2
Nitrous oxide 25
Halogenated gas +nitrous oxide 0.5 + 25
Dental facilities[nitrous oxide alone] 50

15. Components of the scavenger system:
Gas collection assembly.
Transfer tubing.
Scavenging interface .
Gas disposal tubing .
Gas disposal assembly.

16. 1.Gas collecting assembly
Captures excess anesthetic gases
and delivers it to the transfer
tubing.
WAG are vented from anesthesia
system through either adjustable
pressure limiting valve or
ventilator relief valve.
Gas passing through these valves
accumulates in the gas collecting
assembly and is directed to the
transfer means.

17. 2.Transfer tubing
The transfer tubes carries excess gas from gas collecting assembly to
scavenging interface.
The tubes must be either 19 or 30 mm, sometimes yellow color-coded .
The tubes should be sufficiently rigid to prevent kinking and as short as
possible to minimize the chance of occlusion.
Separate tubes from the APL valve and ventilator relief valve merge into a
single hose before they enter scavenging interface.
If the transfer means is occluded, baseline breathing circuit pressure will
increase and barotrauma can occur.

18. 3.Scavenging interface
The scavenger interface is the most important component because it
protects the breathing circuit or ventilator from excess positive or
negative pressure.
Positive-pressure relief is mandatory, irrespective of the type of
disposable system used, to vent excess gas in case of occlusion distal to
interface.
scavenger interfaces may be open
closed

19. B&C closed interfaces
A&B are active systems
C is passive system

20. OPEN INTERFACE:
It contains no valves and is open to
the atmosphere, allowing positive and
negative pressure relief.
Open interfaces should be used only
with active disposable systems that
have 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.

21. The efficiency of it depends on several factors:
A.The vacuum flow rate per min must equal or exceed the
minute volume of excess gases to prevent spillage.
B.Spillage will occur if the volume of a single exhaled
breath exceeds the capacity of reservoir.
Open interfaces
are safer for the patients.

22. CLOSED INTERFACE:
It communicates with the atmosphere through valves.
Two types of closed interfaces are commercially available:
positive pressure relief only
positive and negative pressure relief
POSITIVE PRESSURE RELIEF ONLY:
 It has a single positive pressure relief valve and is designated to be used
only with passive disposable systems.
Transfer of the waste gas from the interface to the disposable system
relies on weight or pressure of the waste gas itself because a negative
pressure evacuation system is not used.
In this system reservoir bag is not required.

24. POSITIVE AND NEGATIVE PRESSURE RELIEF:
 It has positive and negative pressure relief valve in addition to a reservoir
bag.
It is used with active disposable systems.
The effectiveness of a closed system in preventing spillage depends on:
the rate of waste gas inflow
the evacuation flow rate
the size of the reservoir
Leakage occurs only when the reservoir bag becomes fully inflated and
pressure increases sufficiently to open the positive pressure relief valve .
In contrast, the effectiveness of a open system in preventing spillage
depends not only on the volume of the reservoir but also on the flow
characteristics within the interface.

25. 4.Gas disposal tubing
The gas disposable tubing conducts waste gas from the Scavenging
interface to the gas disposable assembly.
It should be collapse proof and should run overhead, if possible to
minimize the chance of accidental occlusion.

26. 5.Gas disposal assembly
It ultimately eliminates excess waste gas.
It is of two types: Active
Passive
Active assembly:
most commonly used. It uses central evacuation system.
A vacuum pump serves as mechanical flow inducing device that removes
the waste gases.
An 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.

27. - Piped Vacuum
- Active duct system - employs flow inducing devices (fans ,
pumps , blowers etc..) to move even at low pressures
Advantages
 Convenient in large hospitals, where many machines are in
use in different locations
Disadvantages
 Vacuum system and pipe work is a major expense
 Needle valve may need continual adjustment

28. Passive disposable system:
 does not use a mechanical flow inducing device.
The weight or pressure from the heavier-than-air anesthetic gases
produces flow through the system.
Positive pressure relief is mandatory, but a negative pressure relief and
reservoir are unnecessary.
Passive – simpler and less expensive but not effective
- Room ventilation system
- Nonrecirculating or – Recirculating
- Piping direct to atmosphere
- Adsorption devices
- Catalyst decomposition

29. Charcoal canisters :
activated charcoal
connected to the outlet of the breathing
system
removes halogenated anaesthetics by
filtration
Catalytic Decomposition :
• Catalytic decomposition can be used
to convert nitrous oxide to nitrogen
and oxygen, reducing its contribution
to the greenhouse effect

30. Advantages
 No set-up cost
 Mobile - moves with the machine
Disadvantages
 Continuing cost of replacement.
 Continuos replacement is messy
 Does not remove nitrous oxide
 Heating the canister causes the release of the
inhalational agents

31. Evaluation of Anesthetic Equipment
Each piece of equipment involved in the delivery of inhalant anesthetics
should be evaluated regularly to assure its function and integrity.
Procedures for checkout of anesthesia equipment, depending on
the equipment to be used, should include the following:
Status of the high-pressure system, including the oxygen supply and nitrous oxide
supply - The nitrous oxide supply should not leak when the cylinder valve
is on and the nitrous oxide flowmeter is off.
Status of the low-pressure system (flowmeter function) - A negative-pressure
leak test should be performed at the common gas outlet or the outlet of
the vaporizer immediately upstream from the breathing system.

32. Status of the breathing system - An appropriate leak test for a circle
system and Noncircle systems can usually be done. The quantity of
leakage can be measured by determining the flow rate of oxygen
necessary to maintain a constant pressure in the system, and the
leak rate should be less than 300 ml/min at 30 cm of h2O.
Status of the scavenging system - The scavenging system should be
properly attached at all connectors, and the appropriate vacuum
should be assured for active systems. If charcoal canisters are
employed for scavenging, they should be changed at appropriate
intervals.
Status of mechanical ventilators - Ventilators should be connected
properly to the anesthesia machine, and an absence of leaks should
be assured.

33. Monitoring of the Effectiveness of
Antipollution Techniques
Monitoring trace-gas concentrations in the workplace provides a
quantitative assessment of the effectiveness of a waste-gas control
program.
Measuring the concentration of anesthetic in the breathing zone of the
most heavily exposed workers is the usual procedure.
An air-monitoring program is most appropriately started after anesthesia
delivery systems have been equipped with scavenging systems and after
other techniques for minimizing waste gas pollution are in place.
 An ideal approach would include frequent air monitoring, preferably at least
semiannual evaluations.

34. Effectiveness
Unscavenged operating rooms show 10-70 ppm halothane, and 400-3000
ppm N2O.
 scavenging brings these levels down to 1 and 60 ppm respectively.
 Adding careful attention to leaks and technique can yield levels as low as
0.005 and 1 ppm.

35. HAZARDS
Scavenging system functionally extends the anesthesia circuit all the way
from the anesthesia machine to the disposable site.
Obstruction of scavenging pathway can cause excessive positive pressure in
the breathing circuit and barotrauma can occur.
 excessive vacuum applied can result in undesirable negative pressures
within breathing system.
Loss of Monitoring Input – it may mask the strong odor of a volatile
anesthetic agent, delaying recognition of an overdose
Alarm failure – neg. pressure from the scavenging system interface prevent
the bellows from collapsing when breathing system is disconnected . Low
airway pressure alarm not activated.

36. Avoiding waste gas exposure
Good mask fit.
Avoid unscavengeable techniques if possible (insufflation).
Prevent flow from breathing system into room air (only turn on agent and
nitrous oxide after mask is on face, turn them off before suctioning).
Washout anesthetics (into the breathing circuit) at the end of the
anesthetia.
Don’t spill liquid agent.
Use low flows .
Use cuffed tracheal tubes when possible.
Check the machine regularly for leaks.
Disconnect nitrous oxide pipeline connection at wall at the day’s end.
Total intravenous anesthesia.

37. THANK U….THANK U….