Presentor : Dr.T.Kumar Moderator : Dr.Venkatesh

(Asst. professor)

SCAVENGING SYSTEM

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

Workplace exposures :

- Hospital-based and stand-alone operating rooms,

- Recovery rooms, - Dental operatories, - Veterinary facilities .

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

Methods of studiesAnimal Investigations

Human Volunteer studies

Epidemiological studies of exposed humans

Mortality studies

ProblemsSpontaneous 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

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

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 sysnthesisCardiac Disease : higher Freq of HTN

and dysrthythmias

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).

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.

TypesScavenging 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.

The 2 major causes of waste gas contamination in the O.R :

1. The anesthetic technique used and 2. The equipment issuesRegarding 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.

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.

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

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

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.

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.

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

B&C closed interfacesA&B are active systemsC is passive system

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.

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.

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.

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 reservoirLeakage 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.

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.

5.Gas disposal assemblyIt ultimately eliminates excess waste gas.It is of two types: Active PassiveActive 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.

- 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

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

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

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

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.

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.

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.

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.

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.

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.

THANK THANK U….U….