Anaesthetic Equipment Flashcards
(178 cards)
1
Q
What medical gases are piped
At what pressure
A
Oxygen 420kpa
Nitrous oxide
Medical air 420 and 700kpa
Medical vacuum
Scavenging vacuum
2
Q
FEatures of medical gas distribution network
A
Copper pipes
Isolation valves to specific areas
Non interchangeable screw threads
Colour coded
Non interchangeable connections for equipment (schrader)
3
Q
What are the features of a schrader valve
A
Labelled
Colour coded
Matched connection (collar indexing)
4
Q
What is the union between the connection hose and medical equipment termed (opposite end to schrader valve
A
NIST union
5
Q
What is hospital oxygen stored in
What does it consist of?
A
Vacuum insulated evaporator
Stainless steel tank with outer steel jacket with vacuum in between for insulation
6
Q
How is oxygen stored in a vacuum insulated evaporator
Temp and pressure
A
Liquid and gaseous oxygen held between -160 and -180oC
Pressure 1100-1300kPa
7
Q
Boiling point and critical temp of oxygen
Implications for vacuum insulated evaporator
A
Boiling point -183
Critical temp -118
Held Below critical temp so can be compressed into liquid by pressure
Held above boiling point at 1atm so must be put under pressure to be in liquid state
8
Q
How can oxygen leave a vacuum insulated evaporator
A
Via a top valve with pressure 6 - 10 bar (600-1000kpa, 6-10atm)
Withdrawn via the bottom as a liquid then superheated to top up during surges of demand
9
Q
What is backup if the vacuum insulated evaporator fails
A
A cylinder bank of oxygen
10
Q
Roughly how long does a vacuum insulated evaporator last
A
Around 10 days
Reserve cylinder bank 1 day
11
Q
How is nitrous oxide stored in a hospital
Crit temp of nitrous and implication
A
Cylinder bank consisting of mixed liquid and gas as below crit temp of 36.5oC
12
Q
How is medical air provided in a hospital
A
Either a compressor (which can lead to contamination with oil mist and water vapour) or a cylinder bank
Delivered at 420kpa for anaesthetics or 700kpa for powering surgical equipment
13
Q
What is the strength of the medical vacuum used for suctioning
A
53kpa (400mmHg)
14
Q
Why is medical vacuum for suction not the same system as for scavenging
A
Suction requires low flow but high levels of vacuum
Scavenging requires high flow but low levels of vacuum
15
Q
What are gas cylinders made of
A
Molybdenum steel
16
Q
What is marked on a gas cylinder
A
Tare weight
Hydraulic test pressure
Identy of gas
Density of gas
Serial number
Owner of cylinder
Manufacture of gas
17
Q
What are the cylinder pressures in kpa of
Oxygen
N2o
Entanox
Air
Co2
Helium
A
Oxygen -13700
N2o -4400
Entanox - 13700
Air -13700
Co2 -5000
Helium -13700
18
Q
Which medical gases are actually presented as vapours?
Why
A
Nitrous
Co2
Entonox is mixed
Their critical temperatures are above room temp
19
Q
Boiling point and critical temp of oxygen
A
Boils -183
Critical -118
20
Q
Boiling point and critical temp of nitrous oxide
A
Boils at -89, critical temp 36.5
21
Q
Boiling point and critical temp of co2
A
Boils at -78.5
Critical at 31
22
Q
Boiling point and critical temp of helium
A
Boils at -269
Critical temp -268
23
Q
At what point does gas separation occur in nitrous
A
-6oC
24
Q
What bodies does the pin index conform to?
A
British standard
International organisation for standardisation
25
Colour of oxygen cylinder
Black
White shoulders
26
Colour of nitrous oxide cylinder
Blue
Blue shoulders
27
Colour of entanox cylinder
Blue
Blue and white shoulders
28
Colour of air cylinder
Black
Black and white shoulders
29
Colour of co2 cylinder
Grey
Grey shoulders
30
Colour of helium cylinder
Brown
Brown shoulders
31
What seal fits over then valve outlet of a gas cylinder
Features
Bodok seal
Gas tight metal and rubber ring
32
Pin index of oxygen
2.5
33
Pin index of nitrous oxide
3.5
34
Pin index of entanox
7
35
Pin index air
1.5
36
Pin index co2
1.6
37
How often should gas cylinders be tested
How
Hydraulic testing with water every 5 years
Endoscopic or ultrasound analysis for internal cracks
38
How is cylinder size classified?
Letters according to water capacity, capacity of gas varies by type.
39
Water capacity of a cd cylinder, e cylinder
Cd 2 litres
E 4.7 liters
40
Oxygen capacity of a size a cylinder
Relationship to increasing Zoe
170l
Doubles at d to 340 then sequential doubling to F
41
How can cylinder contents be estimated?
Comparing actual weight vs tare weight
In the case of the gases (not vapours) - oxygen, air, helium then pressure is directly proportional to mass of gas present
42
How many litres of oxygen are in a E sized cylinder at atmospheric pressure (ie when released)
What law is used
Boyles law Relating pressure to volume
P2.V2=P1.V1
V2=P1.V1/P2 = 13700.4.7/100 = 643.9
43
What is the filling ratio of a vapour cylinder
Ratio of weight of substance compared to weight of water equal to internal volume of cykinder
44
What is the filling ratio of n2o
0.75
45
What cause change in pressure of vapour cylinder
Change in temperature
When all of the liquid has evaporated
46
When do vapour cylinders quickly change temperature, effect on pressure?
On rapid emptying - due to absorption of latent heat of vapourisation causing cooling and pressure drop.
47
Why do patients connected to an o2 cylinder not get 13700 kpa of pressure? What do they get
What else does this do
about 420kpa
Due to a regulator - as high pressure enters device pushes up a diaphragm attached to a spring which is connected to a stopper which partly closes the entry valve. Lower pressure then exits through the outlet which is left unobstructed.
Compensates for variation in demand and cylinder pressure keeping a constant flow.
48
Features of framework of anaesthetic machine
Stainless steel
Electrically earthed
Anti static wheels
49
Features of anaesthetic machine piping
Copper with brazed fixed joints, more recently nylon pipes
Any detachable joints screw threaded and sealed with compressible washer and ptfe tape
Pipes different diameters for different gases to reduce risk of cross connection
50
What makes a nist connection specific for a specific gas?
Other safety features
Non interchangeable threaded nut
Specific diameter shoulder with oring seal
Specific diameter forward shaft
Non return valves and gauze filters
51
Key safety measures built into anaesthetic machine
Secondary pressure regulators - smooth out gas pressure fluctuations
Oxygen failure warning device
Oxygen bypass circuit
52
Features of oxygen failure warning alarm
Name of old design
>60dB
Triggers when o2 supply <200kpa
Power supply comes from oxygen supply pressure
Cannot be switched off or result until oxygen supply restored
When triggered opens fresh gas flow to air
Ritchie whistle
53
What is the oxygen bypass circuit
How much o2 can it deliver
Bypasses the rotameter block and back bar
Can deliver 30lpm
54
Where is the back bar located in the anaesthetic machine
What is found here?
Between the rotameters and the common gas outlet
Vaporisers
55
Rough pressures in the back bar
7-10kpa at Rotameter end
1kpa at outlet end
56
How is the back bar protected from excess pressure if the common gas outlet is occluded, why necessary
Has a blow off pressure relief valve set at around 30kpa
Protects the vaporisers
57
Features of vaporisers connections on back bar
No leak whether vapourised connected or not
Allows easy installation and removal
Locking mechanism to stop more than one being used at once
58
What is the issue if an anaesthetic machine allows multiple vapourisers to be switched on
Mixed gas
absorption of a more voletile agent by an upstream less voletile agent leading to very high release when less voletile agenet subsequently turned on
59
What is the size of the common gas outlet?
Other features
22mm external
15mm internal
Swivel mount (cardif swivel)
Stand bending motion of 10Nm
60
Function of vaporiser
To vaporise
To mix with fresh gas
To deliver reliable concentration
61
Features of voletile which govern characteristics of vaporiser
SVP
Boiling point
MAC
62
How does a variable bypass vaporiser work?
Gas flow spilt into two streams, one bypassing the vaporiser chamber
Gas through the vaporiser becomes saturated with vapour
This is fed back into the bypassing flow wi th the fraction allowed back determining final concentration of the vapour
63
Main types of bypass vaporiser
Plenum vaporiser
Draw over vaporiser
64
SVP, BP and MAC of Sevo
SVP 21.3
BP 58
MAC 2
65
SVP, BP and MAC of Iso
Svp 31.5
Bp 48
MAC 1.15
66
SVP, BP and MAC of des
Svp 88.5
Bp at 23
MAC 6
67
What are the conditions used to give standard values for svp and boiling point
Svp 20oC
BP 100kpa
68
How does a plenum bypass vaporiser work
Fresh gas flow drawn into chamber with saturated vapour then fed out to splitting valve where it mixes with bypassed flow,
69
Resistance of a plenum vaporiser
Implication for ventilation.
Has a resistance of about 0.4kPa/l/min thus to draw a rate of 30lpm on inspiration and spontaneously breathing patient would need to generate 12kpa pressure. This is too high. For it to work the circuit must have a resevoir bag.
70
If the flow through the back bar is 5lpm and 200ml of this goes through the vaporiser what is the flow spitting ratio
4.8/0.2=24
71
Examples of plenum variable bypass vaporisers
Drager vapor
TEC5
72
How does a drawover variable bypass vaporiser work
Features
Inspired gases at atmospheric pressure are drawn through the chamber by inspriatory effort by the patient
Must have very low resistance to flow but can be used directly with the patient with air as a carrier gas
73
Disadvantages of draw over vaporiser
Flow rate varies considerably through resp cycle which means flow through vaporiser also does, this leads to inaccuracy
74
What is the saturated vapour concentration if the svp is 31.5 and chamber pressure 105
SVC = SVP/chamber pressure x 100 = 31.5/105 x 100 = 30%
75
How do measured flow vaporisers work?
Volatile heated in a chamber under pressure equal to its svp
Vaporiser then controls addition of the pressurised vapour to the fgf using a pressure sensor control valve
76
Example of a measured flow vaporiser
TEC6 desflurane vaporiser
77
Why does desflurane need a measured flow vaporiser?
Boiling point of 23.6 thus in a plenum vaporiser would be intermittently boiling and producing an unreliable concentration
78
Features of a tec6 vaporiser
Mains supply with battery back up
Three heaters to boil desflurane at 39oC and prevent re condensation
Electronics with warnings of disconnection and low level
79
How long does it take a desflurane tec 6 vaporiser to be prepared?
What percentage can it deliver
10 minutes
18%, 3 Mac
80
What happens to voletile concentration at high flow rates, why?
What helps mitigate this
Can drop beneath the dialled number as gas is not getting fully saturated
Also at higher flows more vaporisation occurring causing more absorption of latent heat with drop in temperature further reducing vapour concentration
Lower flows or larger area in contact
81
How do vaporisors compensate for changes in temp
Altering splitting ratio with more flow through vaporiser at lower temps
Increase thermal capacity of vaporiser to buffer temp changes (eg filling a compartment with water or incorporate a mass of metal like copper)
82
What would occur if a vaporiser was moved to altitude
Pressure in vaporiser chamber falls thus SVC increases
However, though the concentration is increasing the partial pressure exerted in the tissues will remain the same
83
What is the pumping effect on vaporisors
How to combat
If outlet gas flow periodically obstructed (eg with a minute volume divider or assisting ventilation) then there will be alternating compression and release of gas from the back bar (and thus surges of volatile)
Reduced with one way valves and increasing vaporiser flow resistance
84
What is the effect of increased nitrous oxide concentration on vaporisers
Reduced viscosity and increased density of gas
Decreased gas flow through vaporiser
Nitrous also has increased solubility in volatile agents which can result in its fraction increasing
Small drop in volatile concentration achieved
85
What is the issue with overfilling a vaporiser
Can cause leakage into the back bar and over delivery of gas to the patient
86
What servicing should vaporisors undergo?
Yearly Maintainance
2 weekly drainage and cleaning
87
What product of halothane can build up in vaporisors
Thymol
88
Desirable features of a vaporiser
Large surface area
Large heat sink
Temp sensitive control valve
Accurate splitting valve
Low resistance to flow
Stable mounting
Locking device
Clear gauge
Agent specific filling point
Easy to maintain
89
Distinction between open and closed breathing systems
Closed controls the gas mixture delivered to the patient
90
Subdivisions of closed breathing systems
Rebreathing - inhalation of previously expired gasses, many systems allow this but we overcome it by increasing flow rates
Non rebreathing - can be achieved with valves, flow rates or carbon dioxide absorbers
91
What dead spaces exist in breathing systems
Apparatus dead space - from patient to the expiratory valve
Functional dead space - all areas of system that become contaminated with expiratory gas (can be greater or less depending on system and fresh gas flow)
92
How is efficiency of a breathing system expressed
As minimum fgf to maintain patients minute volume
Eg. Spontaneous magill circuit has efficiency of >0.7
93
What are the diameter of the hoses used in breathing systems
22mm in adult
15mm paeds
30mm scavenging
94
Safety feature in anaesthetic resevoir bag
Low compliance to try reduce development of harmful pressures if system valves accidentally closed
95
What components does the mapleson system consider for classification.
Configuration of:
Resevoir bag
Hosing
Apl valve
Face mask
96
What are the mapleson classification names?
A - magill or lack
B -
C - waters
D - bain
E - Ayers t piece
F - Jackson Rees modification
ADE - Humphrey
97
Description of a Magill circuit
Fresh gas flow and bag at machine end, apl at patient end.
SV - good - tubing cleared out of apl during expiratory pause. FGF = MV
CV - poor - pressure in pause struggles to clear tubing. FGF > 2x MV
98
Description of lack circuit
Coaxial mapleson A,
bag, fgf and apl all at machine end. Return tube can either be inside (risk of rupture making whole system dead space) or running back as separate tube in parallel
Similar principles and flows to magill (SV 1xMV, CV >2xMV) but with apl valve more conveniently located near anaesthetic machine
99
Description of waters circuit
Short, minimal tubing,
bag, fgf, apl, patient
Practical for resus, suitable for sv or cv
100
Description of Bain circuit
Coaxial circuit
Machine end bag and apl valve,
Fresh gas flow down inner tubeing delivered at mask end
Expired air passes back to machine end outlet though outer tube
Again may have a parallel system rather than coaxial
Less efficient for sv (approx 3xMV or 300ml/kg/min) than magill but more efficient for cv (approx <1xMV or 70ml/kg/min)
101
Describe Ayers t piece
Paed circuit
No bag, open tubing, fgf at patient end, no apl valve
Expiratory limb tubing acts as inspiratory resevouir
Needs 2-4x mV to avoid rebreathing
102
Describe Jackson Rees modification
Open ended resevoir bag on end of Ayers t piece
103
What is a Humphrey circuit
Can switch between a magill and a Bain/Ayers for max efficiency in either sv or cv
104
Components of a circle system
Input from ventilator combing with bag and apl valve at a ventilator/bag switch.
Soda lime canister
Fresh gas flow input
One way valve
Inspriatory limb
Patient
Expiratory limb
One way valve
Back to switch
105
Where should the fgf and bag be optimally placed in a circle system for minimum resistance
Between the soda lime and inspriatory valve
106
Advantages of circle system
Very low fgf due to soda lime
Allows recirculating of voletile reducing cost and enviro damage
Low functional dead space due to the removal of co2
107
Disadvantage of circle system
Bulky
One way valves increase flow resistance
108
What is the effect of low and high fgf on flow resistance in a circle system
Low fgf increase inspiratory resistance but decrease expiratory resistance
High fgf vica versa
109
In an older ventilator with a bag in bottle approach what would tidal volumes in a circle system depend on
How does it differ with a modern one
Ventilator settings
Fresh gas flow
Modern sense the Tv delivered and compensate for fgf
110
How can volatiles get used in a circle system
Advantages and disadvantages
VOC out of circuit - FGF through vaporiser then into the circle system. Expired gas dilutes the inspired volatile until equilibrium reached when end tidal voletile conc the same as inspired.
VIC in circuit - inspired gas recirculated through vaporiser continuing to increase in conentration potentially reaching saturation levels.
111
How do carbon dioxide absorbers work?
Co2 dissolved in water to form carbonic acid
Co2 + H2O = H + HCO3-
Then carbonic acid reacts with calcium hydroxide to form calcium carbonate and water
H + HCO3- + Ca(OH)2 = CaCO3- + 2H2O
112
How does the absorption media change as co2 absorbed
Becomes wet - producing more environment for co2 to combine and become carbonic acid
Exothermic - becomes hot driving reaction further
pH increases enabling indicator dye to show calcium hydroxide level
113
When at equilibrium what flow rates are needed in a circle? Why
100-300ml/min
To replace oxygen absorbed and leakages through apl
114
What is in soda lime
80% calcium hydroxide
4% sodium hydroxide
16% water
115
Why is size of soda lime granuals important
Small enough for low space and high surface area
Large enough to leave gaps not to resist air flow
116
How much co2 can 100g soda lime absorb
25L
117
Why is soda lime not used with waters circuit?
To and fro motion of gas can cause inhalation of caustic granules
118
What is soda lime channeling
Passage of gas through channels in the soda lime bypassing much of the granules and not being fully scrubbed
119
What toxic products can soda lime produce and how
Carbon monoxide - volatiles with CHF2 (iso, does, en) pass through dry soda lime produce this. Fairly artificial as soda lime usually wet.
Compound A - sevo decomposes in soda lime to form this, usually only produced at a fraction of toxic levels
Dichloroethylene - a neurotoxin, only produced when used with trichloroethylene (no longer used)
120
How can oxygen delivery systems be described?
Variable or fixed performance
Low medium or high dependency
121
What does fiO2 depend on in variable performance systems?
What can it get up to?
How can it reach this level
Oxygen flow rate
0.9
To get high fiO2 needs a resevoir
Probably also non return valves
122
What are low medium and high dependency systems for oxygen administration
Low spont breathing at atmospheric pressure
Medium spont breathing with support eg cpap
High mechanically ventilated
123
What does fiO2 of variable performance systems depend on
Flow rate
Tidal vol and resp rate
Capacity of system
Use of non return valves
124
FiO2 obtainable using variable performance low dependency systems
Nasal cannula .21 - .3
Face mask .21 - .5
Reservoir mask with NRB valve .21 - .8
125
FiO2 available with a Venturi mask or t piece
What do they require
.24 - .6
Oxygen jet
Venturi device
Reservoir tubing
126
Key parts of resuscitation breathing systems
Examples
Ambu system and laerdal system
Self inflating bag
NRB Valve
Reservoir bag
Oxygen supply
127
Types of NRB valve used in resus bags
Rubén’s valve - spring loaded bobbin - open bag to patient on inspiration, then closed to bag open patient to air on expiration
Ambu valve - movable flaps, mushroom valve
128
Features of a standard endotracheal tube
Non irritant transparent plastic
Toxicity compliance stamp
Internal and external diameter marking
Length markings
Radioopaque line
High volume cuff (to produce lower pressure)
Pilot ballon with self sealing valve
Left facing bevel with eye
129
Special ETT feature
Multilumen
Armoured
Laser resistant
Microlaryngoscopy
Cuffs with foam or water (to prevent nitrous driven expansion)
Anatomically shaped - oxford, Rae
130
Alleged side effects of occupational exposure to anaesthetic gasses chronically
Increased spontanious abortions
Reduced fertility
Increased female births!
Increased minor congenital abnormalities
Vit B12 inactivation
Increased leukaemia and lymphoma
131
Maximum ppm level for
Nitrous
Halothane
Enflurane
Isoflurane
Sevoflurane
Nitrous 100
Halothane 100
Enflurane 50
Isoflurane 50
Sevoflurane 20
132
Why do scavenging systems need a resevoir
Other safety features
To cope with wide variations in flow
Positive and negative pressure relief valves
30mm connections to avoid connecting to wrong valve
133
How does a passive scavenging system work
Issues
Patients expiratory effort expels waste gas down tube to outside atmosphere
Inefficient
Increased resistance to expiration
Risk of obstruction
134
How do active scavenging systems work
Pressure of scavenging system in cmH2O at 30lpm
Remote fan unit produces a sub atmospheric pressure drawing large gas flows down piped system expelling it remotely
-0.5 to +5
135
What absorber can be used to remove voletile
Activated charcoal
136
What methods are there to mechanically ventilate
Positive pressure
High frequency jet
Negative chest wall pressure
137
What are the phases mapleson scheme classifies positive pressure ventilators
Inspriatory phase
Inspiratory cycling
Expiratory phase
Expiratory cycling + inspiratory triggering
138
How can a ventilator deliver an inspiratory phase? How do they fudamentally differ?
Pressure generator - must provide high flow at set pressure thus low internal impedance to flow
Flow generator - delivers a presets flow irrespective of lung compliance so must have very high internal impedance to attenuate the effect of compliance. Gives a fixed tidal volume.
139
Inspriatory and expiratory pressure and flow pattern of a pressure generator ventilator vs flow
Pressure generator - blocked waveform pressure (immediately to set pressure with immediate fall off at end) rapid increase in flow to peak then tails off to 0 at end of inspiration followed by rapid reversal (expiratory flow peak at start of expiration tailing off to 0 at end)
Flow generator - increasing pressure during inspriation to peak at end inspiration with boxed flow (constant at set value through inspiration) expiration similar to that of pressure controlled.
140
Effect of high and low compliance pressure and flow generator vents
Pressure - high compliance runs risk of volutrauma, low compliance causes truncation of tidal volume delivered
Flow - high compliance little effect, low compliance runs risk of barotrauma as high pressure used to deliver set volume
141
How do flow and pressure ventilators reduce risk of volu and baro trauma respectively
Flow - pressure limits and alarms
Pressure - volume limits and alarms
142
How can pressure and flow ventilators compensate for leakage
Pressure - can compensate for small leaks as ventilator acting to deliver presets pressure
Volume - leaked volume will be lost with lower tidal volumes
143
What is simv ventilation
Synchronised intermittent mandatory ventilation
Set number of breaths, allows spontanious breathing,
144
How can tidal volume be calculated from the flow curve?
Area under the curve
145
How can inspriatory Cycling be performed?
Volume cycling - switch to expiration once present volume has been delivered. May include an inspiratory pause to prolong the inspiratory phase.
Pressure cycling - switch to expiration once present inspriatory pressure reached
Time cycling - inspiratory phase duration fixed and switches to expiration at this point regardless
146
How does expiratory cycling occur?
Usually on a timed basis given it is a passive process
Inspiration may be triggered by spontanious effort too in supported or assisted ventilation modes
147
How does a minute volume divider work?
Driven by fresh gas supply
Gas passes into bellows which divide it up into dial volumes
First bellow empties into second bellow
Second bellow delivers tidal volume to patient
148
How does a bag in bottle ventilator work?
Fresh gas enters bag mounted in a bottle
Ventilator compresses bellows by pressurising the bottle
Bag then opens to an expiratory port
Ventilator circuit isolated from patient circuit - often used in anaesthetic machines and microprocessor controlled
149
How do microprocessor controlled electronic ventilators work?
Usually with bellows driven mechanically but controlled electronically for accuracy and ancillary modes to benefit difficult patients
150
How does high frequency jet ventilation work.
When is it Used? Advantages disadvantages
High pressure supply 400kpa to inject through tube.
Used for icu and thoracic surgery
Doesn’t need a sealed airway
Can cause barotrauma and issues with humidiciation
151
Different ancillary modes of ventilation and brief descrition
PEEP - continued pressure in expiration for recruitment
CPAP - continued pressure in insp and expiration to assist spont breathing
Intermittent mandatory ventilation - supply’s a preset number of mandatory breaths per minute and allows patient to breath spontanious with support between them
Synchronised intermittent mandatory ventilation - synchronises the mandatory breaths with patients own
Pressure support - assisted ventilation where ventilator provides support to a patients spontaneous effort
152
How does simv benefit over imv
Synchronisation avoids breath stacking.
153
How can humidity be defined
Absolute - mass of water Vapor in given vol of gas eg g/m3
Relative - ratio mass of water present in given volume of air at given temp against mass of water needed to fully saturate same volume of air at same temperature
154
How much water is found in fully saturated air at 20oC
17g/m3
155
How controlling humidification of air help
Reduces heat and moisture loss
Reduces damage to mucus membrane
Comfort of theatre staff
Risk of static shocks
Corrosion and frost damage to medical pipes, cylinders and valves
156
How should fresh gas be ideally supplied to the patient
At body temp with a relative humidity of 100%
157
What energy loss can patients suffer from the application of non humidified gas
>10W (10% BMR)
158
How does a bottle humidifier work
How effective
Bubble o2 though a bottle of water at room temp
RH of 40%
159
What is the contribution of soda lime to circuit humidity
Reaction produces water with a RH of 60%
160
What is a heat and moisture exchanger
Efficiency
Capsule with a condensing filter (stainless steel mesh) and hygroscopic/hydrophobic material (eg paper with calcium chloride or ceramic fibres respectively)
Capsule of low thermal conductivity plastic so not lost to environment
Fitted in line to circuit
Expired gas passes the capsule and water deposited + heat retained. Incoming dry air then humidified and warmed
RH 60-70%
161
Advantages of hme
Disadvantages
Can be combined with a filter and an etco2 sensor
Increase dead space and flow resistance
Lower efficiency with higher tidal volumes
162
How does a hot water bath work
Efficacy
Hot water tank through which fgf passed
Thermistor at airway feeds back to control tank temp
Large surface area ensures 100% RH if temp set higher than body temp to allow for cooling in the intervening circuit
163
Disadvantages of hot water bath
Risk of scalding and electric shock
Risk of water condensation in resp tract
Risk of colonisation and infection
Needs power supply
164
How do nebulisers work?
Gas jet - high pressure gas fed over top of small tube of liquid (water or drug), negative pressure at orifice entrains water from the tube creating a spray which is broken into small droplets on an anvil. Produces droplets 2-5micrometer
Ultrasonic - uses a 1-3MHz transducer to break up a water feed dripping onto it. Produces droplets 0.5-2micrometer
165
Where are droplets of various sizes deposited from a nebuliser
<1 micrometers alveoli
5-10micrometers trachea and pharynx
166
What is the created RF of a nebuliser
Theroric no upper limit as droplets aren’t vapourised.
167
How fast do art lines flush
3ml/hr
168
Colour of a pulmonary artery catheter tube
Yellow
169
Which reading from an art line is most accurate?
MAP as it is least effected by over or under damping
170
How many drips per ml. In a giving set
20 in an adult
60 in a paed set
171
Mesh size in a blood giving set
Size of a RBC
150micrometers
RBC 8micrometers
172
Adaptations of nerve block needles
Shorter bevel which is hard to get through skin but gives more tactile feel and less trauma to nerve
More USS reflective
Insulated apart from tip for use with stimulator
Plastic tubing for injection to minimise movement
173
Function of the stylet in a spinal needle
Makes needle more rigid
Prevents occlusion with core of tissue
174
Where are the holes on an epidural tip
3 side holes, blind ended tip. - less likely to enter inter vascular
175
Methods of cleaning
Decontamination - physical removal of infected material
Disinfection - killing of non sporting organisms
Sterilisation - killing of all microorganisms including virus fungi and spores
176
Methods of disinfection
Pasteurisation (20 mins at 70oC, 10 at 80 or 5 at 100)
Chemical (formaldehyde, 70%etoh, 0.5 chlorhexidine, 2% gluteraldehyde, hydrogen peroxide, phenol, 10% hypochlorite)
177
Methods of sterilisation
Dry heat 150oC for 30
Moist heat (steam pressure, autoclave)
Ethylene oxide
Gamma irradiation
178
Times for effective autoclaving
30mins at 1 atmosphere at 122oC
10mins at 1.5 atm at 126oC
3 mins at 2 atm at 135 oC
