scavenging & filters & suctioning Flashcards
what is scavenging?
the process of removing anaesthetic waste gases safely from the operating theatre to reduce theatre pollution and protect staff
may be active or passive
tell me about passive scavenging…
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
pros and cons of passive scavenging
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
tell me about active scavenging systems..
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.
safety features of a scavening system
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.
pros and cons of active scavenging system
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.
what are the safe limits for the anaesthetic gases in theatre?
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
what are the concerns around chronic exposure to anaesthetic agents…
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)
what are the methods for reducing pollution in theatre?
ventilation system - 15-20 air cycles per hr
scavenging
circle system
regional anaesthesia
TIVA
what are the key features of an ideal scavenging system?
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.
tell me about the cardiff aldabsorber
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
how many air changes are required in labour?
5 / hour
pros and cons of cardiff aldadsorber?
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.
what types of filters are there and how are they distinguished?
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
what are the different types of breathing system filter?
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.
how many types of filters exist?
5
combination of BSF types and HME
e.g. HME + hydrophobic
HME + electrostatic
hydrophobic alone
electrostatic alone
HME alone
what are the mechanisms that filters
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
which mechanism of filtration is most effective ? which particle size are least filtered.
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
how is the efficiency of a filter measured?
% 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%
how does the efficiency of a hydrophobic and electrostatic filter compare?
hydrophobic is more efficienct
however more deadspace (larger internal volume) and more resistance to flow.
other than efficiency, what other properties of a filter are important to be aware of?
internal volume - hence deadspace
resistance to flow - hence work of breathing
what are the problems associated with filters?
- 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
what is the suction apparatus used for?
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.
what are the components of a suction system?
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
what are the UK standards for suction?
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.
tell me about the central medical vacuum system?
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.
does the central medical vacuum system actually produce a vacuum?
no
a true vacuum contains no matter or pressure (0 bar)
medical vacuum is 40kpa (i.e. 60kpa below atm)
how does a portable suctioning unit work?
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
what is the purpose of the float within the suction apparatus ?
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.
what 2 suction attachments do you know?
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
what is this device
portable battery powered suctioning device
tell me about this device..
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
what is the lowest pressure on a vacuum and why
-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
complications of using suction…
trauma from yanker device - especially if not under vision - both physical and suction effect
can suction away O2 - hypoxia
negative pressure pulmonary oedema or atlectasis
stimulation - vagal and bradycardia, laryngospasm
