scavenging & filters & suctioning

Question 1

what is scavenging?

Answer 1

the process of removing anaesthetic waste gases safely from the operating theatre to reduce theatre pollution and protect staff
may be active or passive

Question 2

tell me about passive scavenging…

Answer 2

consists of
1. collecting system - APL valve with 30mm connecting
2. transfer system - tubing
3. receiving system - rubber bag/ rigid bottle
4. disposal system - tubing that vents into the atmosphere. positioned to help prevent re-entry.

driving force
utilise outside wind and diffusion to carry gases away. also driven by patient expiration

Question 3

pros and cons of passive scavenging

Answer 3

pros
* cheaper and simpler
* theatre ventilation system can assist in the removal or a fan

cons
* inefficient
* outside wind direction can affect and even blow back in

Question 4

tell me about active scavenging systems..

Answer 4

employed in most modern theatres
whereby a vaccuum is used to improve efficiency

consist of
collecting system - APL v +30mm
transfer system - tubing
recieving system - open ended reservoir box
vaccuum to suction air out of the system. - high flow, low pressure system.

Question 5

safety features of a scavening system

Answer 5

both active and passive
safety features
30mm connector
APL valves at -50pa and +1000pa protect from negative and positive pressures.
hosing is non-compressible and kept away from floor so it cant be occluded.

passive - mesh on outlet to prevent insects getting in.

active - open ended recieving system to prevent negative pressures taking air from patient.

Question 6

pros and cons of active scavenging system

Answer 6

PROS
* efficient
* can create large flow rate - 75L/min and thus likely to be able to clear waste at a range of FGF

Cons
* costly
* excess positive pressure e.g. if it gets blocked can lead to barotrauma.
* risk of negative pressure and pulmonary oedema or deflate reservoir bag and result in rebreathing.

hence pressure relief valves put in place.

Question 7

what are the safe limits for the anaesthetic gases in theatre?

Answer 7

over an 8 hour period, the control of substances hazardous to health (COSHH) regulatory body state..

100ppm = N20
50ppm = iso and en
20ppm = sevo
10ppm = halothane

Question 8

what are the concerns around chronic exposure to anaesthetic agents…

Answer 8

sevoflurane - spontaneous abortion, lymphoid tumours

chronic N20 - oxidises colbolt ion of vit B12 stopping it from being a co-factor for methionine synthase. reduces DNA replication - megaloblastic anaesmia and subacute degen of cord (reduces myelin)

Question 9

what are the methods for reducing pollution in theatre?

Answer 9

ventilation system - 15-20 air cycles per hr
scavenging
circle system
regional anaesthesia
TIVA

Question 10

what are the key features of an ideal scavenging system?

Answer 10

easy to set up
cheap

safety
- pressure releif valves to prevent negative/ positive pressure
- disposes gas safely and not to other theatres/ back in
- 30mm connector

functioning
- efficient
- can deal with various flow rates
- not affected by outside conditions
- separate vaccuum system from suctioning otherwise will interfer with this.

Question 11

tell me about the cardiff aldabsorber

Answer 11

this is a passive, portable scavenging system
can be connected to the breathing system via the APL valve

constists of activated charcoal granules
as halogenated anaestheric agents pass through they are adsorbed by charcoal
the canister gets heavier as more anaesthetic agent is adsorbed
once it is fully saturated, the canister can be heated to allow the anaesthetic agent to be removed in a safe place
this recycles the canister.

does not scavenge N20

Question 12

how many air changes are required in labour?

Answer 12

5 / hour

Question 13

pros and cons of cardiff aldadsorber?

Answer 13

pros: cheap and easy to set up and portable

cons: doesnt remove N20, cant tell when exhausted unless its weighed. requires replacement every 12 houts in use. heating the canisters releases the volatiles back into atmosphere.

Question 14

what types of filters are there and how are they distinguished?

Answer 14

breathing system filters - protect against viruses and bacteria - yellow

heat and moisture exchnage filters - conserve heat and moisture of inspiratory gases - blue

combination of above = green

Question 15

what are the different types of breathing system filter?

Answer 15

this depends on their material
hydrophobic filters - pleated membrane filters microbes. more efficient and lasts longer. however more resistance to breathing.

electrostatic filters- works through electrostatic charges and attraction. less dense than hydrophobic therefore less resistance to breathing. however much less efficient when they get wet.

Question 16

how many types of filters exist?

Answer 16

5
combination of BSF types and HME
e.g. HME + hydrophobic
HME + electrostatic
hydrophobic alone
electrostatic alone
HME alone

Question 17

what are the mechanisms that filters

Answer 17

in ascending size order of particles affected (except electrostatic attraction that depends on charge)

brownian diffusion - small particles are able to diffuse - randomly moving and may randomly collide with filter.(D)

interception - gas flows in streamlines and partilces collide and adhere to filter (a) - following the flow of gas and are small but because of close proximity will collide

intertial impaction - gas flowing in streamlines can pass around the object, however particles with mass cannot change direction and pass around the object and thus instread collide with the filter (B). typically larger particles than in interception

gravatational settling - larger particles fall with gravity and can settle onto the filter (C)

electrostatic attraction

Question 18

which mechanism of filtration is most effective ? which particle size are least filtered.

Answer 18

depends on particle size
e.g. for small particles = brownian diffusion
e.g. for large particles = gravitational setting

in generall combined efficiency of all mechanisms filters , particles of 0.05um to 0.5um pass through the filter more easily than others, with lowest efficiency at 0.3um

Question 19

how is the efficiency of a filter measured?

Answer 19

% of penetration of particles at a particular size.

filter is exposed to aerosol of particles of a particular size and the number of particles getting through is measured
% penetration = the number that got through/ number leaving the aerosol

hence the lower the penetration the better the performance of the filter.

usually particles of 0.2um are used to test filters and at flows of 15 or 30L/min for paediatric and adult filters respectively
usually denoted as nominal rating of a certain percentage
e.g. N99 = 1% penetration of particles at 0.2um
e.g. N95 = 5%
e.g. N100 = 0.03%

Question 20

how does the efficiency of a hydrophobic and electrostatic filter compare?

Answer 20

hydrophobic is more efficienct
however more deadspace (larger internal volume) and more resistance to flow.

Question 21

other than efficiency, what other properties of a filter are important to be aware of?

Answer 21

internal volume - hence deadspace
resistance to flow - hence work of breathing

Question 22

what are the problems associated with filters?

Answer 22

• Increased dead space
• Increased resistance to flow
• Can become blocked with secretions and water – should be replaced if visible
• Increases no. of connections and thus risk of disconnection
• Filter performance reduced with higher gas flows. Normally challenged at 30L/min – if gas flows exceed this e.g. in coughing some microbes may be released

Question 23

what is the suction apparatus used for?

Answer 23

airway secretions, blood, vomitting to reduce risk of aspiration
endotracheal suction to unblock ET tube
suction of NG tube before intubation/ extubation

by surgeons - to remove blood from surgical field, for wash out.

Question 24

what are the components of a suction system?

Answer 24

method for generating vacuum
* electrical pump - piston or rotating vane
* mechanical - foot pump
* bernoulli/venturi

reservoir box to collect - with scale to measure volume - too small will need frequent changing, too large will

The suction tubing should be flexible and firm to prevent collapse; transparent, so that the contents aspirated can be visualized

vaccum control box
* on and off switch - dial at the wall
* manometer to measure pressure
* filter
* valve to control amount of vaccuum
* turn off suction/ flow when box is full

Question 25

what are the UK standards for suction?

Answer 25

60kpa below atmospheric (i.e. 40kpa)
40-60 L/min
take no longer than 10 secs

It is recommended that there are at least two vacuum outlets in each operating theatre, one per anaesthetic room and one per recovery or ICU bed.

Question 26

tell me about the central medical vacuum system?

Answer 26

centrally located vacuum plant which generates sub atmospheric pressure.

consists of multiple electrically driven rotatine veins which pump air out to reduce pressure.
A reservoir which is 40 kpa (60kpa below atm)
reservoir is connected to pipeline system for supply around the hospital.

suction devices can be connected to pipeline outlets via schrader valves - coloured yellow and labelled suctioning.

Question 27

does the central medical vacuum system actually produce a vacuum?

Answer 27

no
a true vacuum contains no matter or pressure (0 bar)

medical vacuum is 40kpa (i.e. 60kpa below atm)

Question 28

how does a portable suctioning unit work?

Answer 28

pipeline is not used here. useful for transfers and where pipeline not available.

barrery powered rotary or piston pumps
us bernoulli principle and venturi effect

gas is passed through a constriction, velocity increases, pressure drops
hole is created to allow suction of matter

Question 29

what is the purpose of the float within the suction apparatus ?

Answer 29

sits at top of fluid level
when fluid reaches top of resevoir the float occludes the suction outlet
prevents fluid entering pump
hence prevents contamination

can also be called a valve

In order to further protect the pipeline
from contamination, a suction trap is integrated into the pressure regulator unit.

Question 30

what 2 suction attachments do you know?

Answer 30

yanker - commonly used for airway/ surgical suction. more rigid larger attachment, transparent. angulated head for positioning in oropharynx. the rigidity carrier risk of trauma.

endotracheal suction catheter - smaller attachment, made of flexible transparent plastic, can go down tube and unblock via suckin secretions. there is a vacuum control port which if occluded by finger allows for suction

Question 31

what is this device

Answer 31

portable battery powered suctioning device

Question 32

tell me about this device..

Answer 32

wall suctioning unit
shows on off switch
and dial to create negative pressure

then a barometer that reads gauge pressures.
i.e. -20kpa = 80kpa pressure
goes up to -100kpa

Question 33

what is the lowest pressure on a vacuum and why

Answer 33

-101.3 kpa
cant get less than 0 absolute pressure
because absolute pressure is measured relative to a perfect vacuum, which is considered zero pressure. By definition, you cannot have a pressure lower than zero, so absolute pressure cannot be negative