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Anaestheska III Week 5+ Flashcards

1
Q

What are the properties of an ideal breathing circuit?

A 
Simple and safe
Deliver intended fio2
Spont and controlled vent
Low FGF requirement
Protect from barotrauma
Remove waste
Easy maintenance and low cost
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2
Q

What is dead space?

A

Where no gas exchange occurs

There is a mix of inspired and expired gases

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3
Q

How does the APL valve work?

A

Lightweight disk sits on knife edge seating held on by spring
Tension in spring = valve opening pressure
Dial movement adjusts the tension

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4
Q

What are safety issues with APL?

A

Malfunction could keep APL open = ^^ dead space
High positive pressure if left closed resulting in barotrauma - safety relief valve at 60cmh20
Exhaled water vapour may cause disk to stick - hydrophobic material

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5
Q

Describe the reservoir bag.

A

Ellipsoidal, anti-static rubber
0.5-2L size
Accommodates FGF during expiration as reservoir for next inspiration
Can assist ventilation and act as visual aide for spont breathing
Highly compliant so accommodates gas limiting the pressure to 40cmH20

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6
Q

Describe circuit tubing.

A

Must provide laminar flow: uniform shape and large diameter
Must have optimal compliance
Corrugations a resist kinking and improve flexibility

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7
Q

What is the design of the mapleson A magill system?

A

Bag in middle
FGF opposite end
APL patient end

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8
Q

How does the Magill system work?

A

Insp: APL closes, FGF comes in and mixes with exhaled dead space gas
Exp: pt expires forcing APL open, bag is refilling
Pause: exp gas meets FGF in tube and is forced out APL

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9
Q

Pro vs con for magill circuit?

A

Yes spontaneous
FGF=MV
No controlled
3xMV needed

Large dead space not for

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10
Q

How does the Lack system work?

A

Insp: APL closes and FGF comes in outer tube
Exp: patient expires into tube so APL opens; FGF fills bag
Pause: expired gas forced through inner tube and out APL by incoming FGF

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11
Q

Pro vs con of lack?

A

As with Magill
Risk of inner tube malfunction causing high dead space
APL at machine end makes system less cumbersome

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12
Q

What is the design of the Mapleson B system?

A

Bag one end
FGF, patient and APL at other
Corrugated tube in middle acts as reservoir

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13
Q

How does the Mapleson B work?

A

Insp: mix of alveolar and FGF inhaled
Exp: expires into tube and bag; APL opens
Pause: expired gas and FGF forces out

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14
Q

Pro vs con for Mapleson B?

A 
No spontaneous
FGF 2x MV needed
No controlled
FGF 2x MV needed
Gas waste and pollution
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15
Q

What is the design for the Mapleson C?

A 
(Waters without absorber)
Bag one end
FGF, patient and APL other 
Short tube 
Used in emergencies
Works like Mapleson B
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16
Q

What is the design for the Mapleson D-Bain system?

A 
APL and bag one end
FGF and patient at other
Co-axial (also parallel version)
Inner tube FGF
Outer tube expired gas
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17
Q

How does the Bain system work?

A

Insp: FGF flow to patient via inner tube
Exp: expires into reservoir tube which mixes with the still flowing FGF
Pause: FGF washes expired gas out, also filling system with FGF for next inspiration

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18
Q

Pro vs con for Bain system?

A 
No spontaneous 
FGF 2xMV needed
Yes controlled
70ml/kg needed
Good for head/neck surgery
Low R and dead space
Assisted scavenging
Inner tube may fail
Bag movement not good indicator
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19
Q

How does the Ayres T piece work?

A

Insp: FGF flow to patient from reservoir tube
Exp: expires into reservoir tube which mixes with FGF still flowing
Pause: FGF washes expires gas out; fills system with FGF for next inspiration

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20
Q

Pro vs con for Ayres T piece?

A 
Yes spontaneous 
3x MV needed
Yes controlled
FGF=MV due to longer exp pause allowing refill time
Low R and dead space
Valveless - less leaks
Pollution and gas waste
Tube length long enough to not entrain air
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21
Q

How does the Jackson Rees Modification work?

A

As with Mapleson E

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22
Q

Pro vs con for Jackson Rees modification?

A 
Yes spontaneous and controlled
2.5-3x MV needed
Visual respiratory movements
Easy IPPV
Tubing length vs entrainment
Pollution and gas waste
Great
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23
Q

What is the design of the Mapleson A Lack system?

A

Co-axial version of A designed to assist scavenging
Inspiration outer tube, exp inner
Parallel version also available
FGF, APL and bag machine end

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24
Q

What is soda lime for?

A

Absorbs carbon dioxide
Low FGF requirement so highly efficient
Low pollution
Conserves, warms and humidifies

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25
What is the physical design of the soda lime canister?
Vertical Two ports: one delivers insp gas, other receives exp gas Each port has unidirectional valve
26
What happens if carbon dioxide rebreathing occurs?
Acidosis results | Acts as an anaesthetic and will cause coma
27
What are the components of soda lime?
94% calcium hydroxide Sodium hydroxide Potassium hydroxide Water pH 13.5 Colour change ethyl violet dye <10
28
Why is silica added to the soda lime?
Granules prone to powder formation which can cause high resistance and stick to valve The silica helps to harden and prevent powder formation
29
Why is zeolite added to soda lime?
Helps maintain pH for longer and retain moisture to increase the amount of carbon dioxide absorption Also helps reduce formation of carbon monoxide and compound A
30
What are the risks of soda lime?
``` Dust on valves Dust cause high resistance Corrosive (alkaline) Compound A Carbon monoxide Channeling Leaks ```
31
What is the granule size of soda lime?
4-8 mesh (4-8 openings per inch) 3-4mm spheres which allow more even gas flow throughout. Also allows longer life, lower dust and reduced resistance
32
What's the mechanism of soda lime?
Exhaled gas go to canister where carbon dioxide gets absorbed and heat + water is produced (exothermic) This warm/humid gas then rejoins FGF
33
Why does low FGF exhaust like faster?
Most exhaled gases go out the APL but with low flows very little exits the APL so therefore goes through the lime
34
What are the safety features of soda lime?
``` Clear canister houses valves and lime Colour change Sphere, specific sized granules Added silica Uneven canister filling can result in channeling ```
35
How is compound A formed?
When sevo used with soda lime Due to alkali metal in lime degrading the sevo Increased by temp, low FGF and high sevo concentration
36
How is carbon monoxide formed?
When volatiles containing CHF2 moiety (enf, des, iso) used with dry granules Production of carboxyhaemoglobin can occur
37
What is a closed system?
No gas escapes FGF replaces what is consumed by patient and lime FGF and pollution both very low FGF must match perfectly
38
What is a semi closed system?
Pressure relief valve allows excess gas to escape | High flows can be used
39
What may happen if unidirectional breathing valves fail?
Low efficiency Rebreathing Hypercarbia
40
What is the unit of measurement for theatre pollution?
Ppm | Particles per million
41
What are some methods to reduce theatre pollution?
``` Theatre ventilation with 15-20 air changes per hour Non-recirculated Circle system TIVA RA Scavenging ```
42
What are some causes of pollution?
``` Bad mask fit Paed breathing systems Failure to turn of gases at end and to intubate Uncuffed tube Vaporiser filling Exhaling vapour in recovery Machine leaks ```
43
What's the ideals of scavenging?
``` Not affect ventilation Not affect dynamics of system Collecting device, system to carry away and method for regulating pressure Checked daily Passive/active ```
44
Describe passive scavenging.
Simple, no cost Collecting system has shroud connects to APL 30mm connector Receiving system can be used (2 valves protect against high and negative pressures) Disposal via copper pipes to atm or ventilation system Driven by patient effort
45
What is the safety features of passive scavenging?
Valves to protect from high and negative pressure 30mm/19 connection prevent connect to breathing system Wind at outlet causing +/- pressure Outlet should have mesh Protect the tubing to prevent leaks Need long tubes (^R)
46
Describe active scavenging.
Collection and transfer similar to passive Receiving system usually valveless, open ended reservoir between receiving and disposal Antibacterial filter downstream Flow indicator between reservoir and disposal Reservoir has 2 valves Vacuum created by fan, pump or Venturi system Cope with 30-130L/min rates
47
What are safety features of the active scavenging system?
30/19mm connector Receiving system capable of coping with changes in flow rates Increased demand (-P) allow ambient air to entrain so maintaining pressure Opposite occurs with high +P occurs Reservoir prevents -/+P to patient Independent pump used
48
What are the order of components for active scavenging?
``` From expiratory valve: 30mm connection Collecting system Transfer system Receiving system Vacuum generator ```
49
What are the features of an ideal filter?
``` Filter air and liquid borne from 99.99-99.999% Bidirectional Minimal dead space Minimal resistance Unaffected and not affect agent Work when wet and dry Prevent liquids passage Light, not bulky, not traumatic Humidify Transparent Low cost ```
50
What are the basic components of a filter?
2 ports: 15mm and 22mm Sample port on anaesthetic side Filtration element in middle
51
What is an electrostatic filter?
Material exposed to electric field producing felt-like material and high polarity. One type of fibre becomes + and other - Usually 2 polymer fibres used Flat layer of material used so low R Relies on charge to attract particles 99.99% effective Charge efficiency high when dry but low when wet and increases R Charge decays with time so limited life
52
What happens when a hygroscopic layer is added to electrostatic filter?
= HMEF | Pressure drop across element and therefore resistance is higher with water absorption
53
What is a hydrophobic filter?
Lasts long periods Rely on natural electrostatic interactions 99.999% efficiency Pleated paper of inorganic fibres achieve high SA and higher R Forces between H2O are > forces between H2O and filter therefore it collects on surface without absorbing
54
What are the characteristics of the ideal filter?
``` Provide humidification Low resistance Low dead space Microbiological protection Maintain body temp Safe and convenient Economical ```
55
What is a HME?
Heat and moisture exchanger Passive and effective Retains a portion of expiratory moisture + heat It then returns it on inspiration Achieves 60-70% Warmed to 29-34 degrees Delivers absolute humidity of 30g/m3 at 30 degrees
56
How does the HME work?
Exhaled gas passes causing water vapour to condense on cooler HME medium. This is evaporated and returned to patient with next inspiration, humidifying gas. >temp difference = > transfer 5-20mins before optimal 0.2 nanometer pore size = HMEF
57
What might affect the HME performance?
Water vapour content and temperature of insp/exp Flow rates - how much time gas is in contact with medium Larger medium = better performance Low thermal conductivity helps maintain temp difference across HME
58
What are the safety features of a HME?
``` May obstruct from mucus or water Single use Max 24hours use: risk of H2O accumulation = ^R Efficiency low with ^TV 2 way gas flow required to work Place close to patient Increases dead space and R (WOB) ```
59
What are the components of a hot water bath?
Disposable reservoir with inlet and outlet for insp gas to pass Heated sterile water partly filled Thermostat controlled element with temp sensors in reservoir and near pt Tubing delivers gas to pt Water trap along tubing between pt and humidifier (lower than pt) Electric power
60
Describe the receiver system for the AGSS?
Main interface between breathing and disposal system. Must protect from +/-P Provides capacity to cope with peak flows Can be open: reservoir tubular open to atm therefore providing air break (needs active disposal) Closed: reservoir is bag with P release valves
61
Describe the disposal system for the AGSS?
Passive: driven by respiration, tube from patient to outside, short and wide tube to reduce R Active: fan/pump draws gas, used with open receiver system
62
What are the affects of dry and cold gases?
``` Dehydration Hypothermia Infection Atelectasis/shunt Reduced FRC Reduced compliance Cell damage - dysfunction mucocilliary elevator, damaged cilia Thick mucus ```
63
What is a nebuliser?
Produces most of micro droplets of water suspended in a gaseous medium Amount of water droplets delivered does not depend on temperature Smallest droplets more stable and get further in airway Can deliver medicine
64
How does a gas driven nebuliser work?
Capillary tube with bottom end in water container Top end close to Venturi constriction High pressure gas flows through Venturi = -P H2O drawn up capillary tube and broken into fine spray Smaller droplets achieved as spray hits anvil/baffle Mostly 2-4 micrometer produced
65
How does a spinning disk nebuliser work?
Centrifugal force created by motor driven spinning disk causes micro droplets to be thrown out
66
What is a laryngoscope?
Perform laryngoscope and aide intubation Handle - houses battery Blade connects to handle Light source: bulb screwed onto blade, electric connection made when open Light can be in handle or transmitted along fibre optic
67
How does a laryngoscope work?
Blade advance and lifts epiglottis to view cords 4 Mac sizes Left blade available Interchangeable blades on handle: ISO international standard - colour marks same systems (green)
68
How does a straight blade work?
Advanced over posterior border of epiglottis which is lifted upward/forward in order to view larynx
69
How does a curved blade work?
Inserted at right angle Sweeps tongue to left Tip reaches vallecula which pulls epiglottis up from behind
70
What is a McCoy blade?
Like Mac but with hinged tip operated by lever at handle | Also available as straight blade
71
What are the safety features of laryngoscopes?
Can cause trauma Light source may fail Large cheat difficult - short handle or angled blade Needs sterilisation
72
What is the polio and kessel blade?
At angle to help with DI Polio 135 degrees Kessel 110 degrees
73
What is a fibreoptic scope?
Aide intubation Evaluate airway Confirm placement Perform trachea bronchial toilet
74
How does a fibreoptic scope work?
Uses light transmitted through fibres Fibres provide low refraction Light enters at a specific angle, travels fibre repeatedly striking and reflecting glass at same angle until it comes out the end Each fibre carries small part of the picture so arrangement crucial throughout scope Variable cord length and diameter
75
What are safety features of fibreoptic scopes?
``` 3.0-7.0 diameter tubes useable Easily damaged Needs reprocessing Light failure Blocked channels Only use one channel at a time ```
76
What are magill forceps?
Small/large | Used to guide tube, remove foreign body, insert throat pack
77
What's a retrograde intubation set?
Assists DI 18G intro needle, guide wire, 14G hollow guide catheter with distal side port, 15mm Intro inserted into cricoid membrane Guide wire advanced in retrograde direction to exit oral/nasal Catheter inserted antegrade into trachea Tube introduced over catheter
78
What are the features of an ET tube?
``` PCV/silicone Radio opaque line Outer/inner diameter Beveled tip Cuff Murphy eye Vocal cord indicator 15mm connection Level markings (cm) Single use marking Pilot cuff One way valve Oral/nasal marking Curvature ```
79
What is the bevel for?
Left facing and oval shaped Improves view of cords when laryngoscope inserted on the right Shape allows to push through cords, separating them
80
What is a high pressure, low volume cuff?
Prevents passage of secretions High pressures on walls of airway Can cause necrosis
81
What is a low pressure, high volume cuff?
Pressure applied over larger area so less pressure risk over longer time Possible wrinkles so less reliable seal
82
Why should pressure be regularly checked?
May increase with nitrous oxide use and temperatures Could be a slow leak Movement from moving patient Nearby surgery
83
Why is a nasal tube advantageous?
Can't bite More tolerated Frees up the mouth Epistaxis risk
84
What are 8 risks of intubation?
``` Linking Herniated cuff Occlusion by secretions Bevel against wall Oesophageal intubation Trauma - sore throat Dental damage Failed airway ```
85
What is an armoured tube?
``` Plastic or silicone rubber Embedded spiral of metal or tough nylon Had a thicker wall so OD bigger Wire prevents kinking Strong, flexible Introducer often used Cannot cut to length High risk bronchial intubation 2x markers for vocal cords ```
86
What is a RAE tube?
``` Ring, Adair, Elwyn Preformed shape Bend where tube emerges so that connection at chin/forehead High risk bronchial intubation Cuffed RAE = 1 Murphy eye Uncuffed = 2 Murphy eye ```
87
What is a laser tube?
Withstand carbon dioxide or potassium-titanyl-phosphate laser Reduce fire and damage risk Beams are reflected and de focused to reduce strike of healthy tissue Flexible stainless steel body or wrap of laser proof foil Double cuff for extra protection Cuff may be filled with meth blue or saline
88
What's an evoked potential tube?
``` Used if risk of nerve damage Bipolar stainless steel contact electrodes are embedded in tube above cuff where they touch cords This is connected to a nerve stimulator Earth connects to patient Provide visual and audible warnings NIM = neural integrity monitor ```
89
What is a micro laryngeal tube?
Better excess to larynx Small diameter; same length Sufficient length for nasal too Ivory PCV to reduce trauma
90
What are the components of a tracheostomy tube?
Introducer Wings on proximal part allow fixation Adjustable flange to fit variable thickness of tissue Cuff/uncuff 15mm Square tip to reduce obstruction risk against tracheal wall Suction lumen above cuff Some have inner cannula: secretions can collect/dry out (obstruction) on inner which can then be replaced instead of whole thing Neonate to adult size Some have one-way flap valve and window for speech
91
What are the benefits of a tracheostomy?
``` More comfort Less sedation needed Better access for oral hygiene Allow oral nutrition Aides bronchial suction Less dead space Less resistance Less glottis trauma ```
92
What are the safety features of a tracheostomy?
``` Haemorrhage Mis placement, occlusion Pneumothorax Blocked by secretion Infection Over inflation Granulomata Tracheal dilatation Scar ```
93
What is a fenestrated tube?
Window in curve channels air to cords allowing speech After deflation patient can breathe around cuff, through window and through tube - less R and weaning May be fenestrated inner cannula
94
What is a larnygectomy tube?
Cuffed tube inserted through tracheostomy to facilitate IPPV during neck surgery Offer better access by allowing breathing system to be connected away from field Replaced with tracheostomy at end
95
What is a speaking valve?
One way speaking valve can be fitted to tube (if cuffed must be down) Mounts on top
96
What's a tracheostomy button?
Once tracheostomy removed, button inserted into stoma to keep patent and allow suction still
97
What's a percutaneous tracheostomy tube?
Insert between 1+2 or 2+3 ring Withdraw any tube to tip just below cords Insert intro needle and seldinger guide wire through to trachea Use F/O throughout, ensure midline puncture, free of tube, posterior wall not damaged and assess position Forceps/dilatory dilate tissue over wire Trache inserted over wire then remove Can be done at bedside
98
What is a double lumen tube?
Selectively deflate one lung while vent other 2 separate colour codes lumen: tracheal and bronchial Each have bevel and cuff with colour coded pilot balloon, labelled 2 curves: standard anterior to fit trachea and other for L/R Y connector - each lumen to limb
99
What is a left DLT?
Inflates left lung and deflates right lung ALWAYS USE Left lobe to carina is 5cm
100
What is a right DLT?
Inflates right lung and deflates left lung Risk of upper lobe obstruction Eye in bronchial cuff to facilitate vent of upper lobe Right lobe to carina is 2.5cm
101
How is position of DLT checked?
Use F/O Auscultation Inflate tracheal until no leak - both lungs vent Clamp tracheal Inflate bronchial until no leak (3ml) - one lung vent Check other lung vent by clamping bronchial and opening tracheal - one lung vent
102
What is an endobronchial blocker?
Alternative to DLT Blocker catheter with distal cuff, pilot balloon and guide loop Multi port adaptor - 15mm Blocker advanced over F/O using loop and tracked into main bronchus Inflate cuff when in place Vent maintained in other lung via tube
103
What is an oropharyngeal airway?
Anatomically shaped device fits into oropharynx to maintain airway patency Anaesthetic reduces tone resulting in obstruction by tongue or soft palate 000-6
104
What are the components of an oropharyngeal airway?
``` Curved body Inner channel Flat anteroposteriorly Curved laterally Flange to prevent travel Bite portion is straight and prevents occlusion Colour code ```
105
How does oropharyngeal airway work?
Keeps airway patent by preventing tongue and epiglottis from falling back Size = distance from incisor to mandible angle or corner of mouth to tragus Adult: Insert upside down partially then rotate 180 degrees - prevent tongue being pushed back Paed: insert right way up and depress tongue if needed
106
What's a Bergman airway?
Assists with F/O Guides F/O Maintains airway and protect scope Side opening allows removal of F/O
107
What are the risks of an oropharyngeal airway?
Trauma to tissue Broken teeth Could trigger gag Can make worse if incorrect fit
108
What is a nasopharyngeal airway?
``` Through nose to nasopharynx Distal end sits just above epiglottis Curved body Left facing bevel Proximal flange Softer plastic ```
109
What's the mechanism of a nasopharyngeal airway?
Alternate to oropharyngeal of mouth won't open or not tolerated Need lubrication Left bevel eases insertion through right nostril
110
What are the safety features of nasopharyngeal airways?
Don't use if on blood thinners, deformities of nose or sepsis Don't force - false passage Too big may cause necrosis
111
What are the advantages of a supraglottic airway?
``` Don't need direct vision Quick Low CVS disturbance Low coughing Conduit for intubation - aperture aligns with glottic opening Useful in CICO 2nd generation has gastric port ```
112
What are the components of a laryngeal mask?
``` Transparent tube Wide diameter (low R) 15mm Elliptical cuff Forms seal around posterior larynx Inflates via pilot balloon with valve Bars to prevent epiglottis obstruction ```
113
What are the components of a proseal?
Lumen adjacent to airway traverses floor of mask to tip to drain secretion/air Contained in bite block 3D elliptical cuff inflation with 2nd cuff behind bowl to improve seal (rear boot or dorsal cuff) Seal up to 35cmH2O
114
What is a reinforced LMA?
Stainless steel wire spiral in wall | Flexible, kink resistant
115
How do you check an LMA?
``` Inflate and check for hernia Check lumen patent Tube bends to 180 degree without occlusion Inspect for faults, damage, wear Inspect when removed for blood ```
116
What is an I-gel?
``` Extraglottic airway Anatomical fit without cuff Has second drain tube Large lumen 15mm Non-inflatable gel like cuff with ridge at superior anterior edge to prevent epiglottis occlusion Wise oval cross sectional body to prevent rotation and bite Gel material moulds into place ```
117
What is a seldinger technique?
Obtain access to lumen Lumen penetrated by needle, wire passed through, needle removed, then catheter passed over wire Risk haemorrhage, perforation organ, infection, equipment loss inside
118
What is a face mask?
``` Anatomic fit Range of sizes Air filled cuff supports body - helps snug fit 22mm Transparent Flavoured Size proportional to dead space Valve to change cuff volume ```
119
What is a catheter mount?
``` Flexible link between system and airway Variable length Corrugated tubing Concertina design 15mm and 22mm ends May have inbuilt sample port or humidifier ```
120
What is ECG?
Electrocardiogram Measure electrical activity of heart with potentials of 0.5-2 MV at skin Shows HR, ischemia, arrhythmia, conduction No assessment of output or function Bipolar leads measure change between 2 electrodes
121
What are the components of ECG?
Skin electrodes: Silver/silver chloride electrode Held in cup separate from skin by foam pad and conduction gel Colour coded cable to machine Variable length and no. Electrodes Must be all one length in set to reduce electromagnetic interference
122
How does ECG work?
``` Clean skin, abrade, good gel contact, all same type Less impedance on bony prominence High/low pass clean signal Signal boosted by amplifier 3-lead most common: 2 active 1 earth ```
123
What is the CM5 arrangement?
R- manubrium sternum L- 5th intercostal space L anterior axillary N- L shoulder Detects ST changes very well! Lead II ideal for arrhythmias!
124
What are safety features of ECG?
Incorrect placement Muscular interference Diathermy current travel here if pad not on correctly High/low ventricular rate alarms and ST segment monitor Raised ST can show early ischemia Interference from mains, diathermy
125
What is Einthoven's triangle?
``` Arrangement of 3-lead Lead II follows direction of depolarisation so is best Dot 1 (R) always - Dot 3 (L) always + Dot 2 varies depending on lead set Unused dot is earth Heart current travels from - to + ```
126
What is a 5-lead ECG?
Utilises V1 which gives view of heart directly below it More comprehensive picture, better arrhythmia analysis, better ischemic monitor, more balance representation of right and left heart V1 is right stern all border, 4th space
127
What creates an upright or upside down ECG trace?
Depolarisation toward + dot is upright If travelling away it creates inverted wave
128
What is DINAMAP?
Device for indirect non-invasive automatic mean arterial pressure
129
What are the components of NIBP?
Microprocessor controls sequence and pneumatic pump Pneumatic pump causes inflation Solenoid valve causes deflation Pressure transducer detects oscillations
130
How does NIBP work?
Microprocessor control sequence of inflation via pneumatic pump Pump inflates cuff to higher P than previous systolic Solenoid valve deflates incrementally Return of flow causes oscillations sensed by transducer and interpreted by microprocessor
131
What are safety features of NIBP?
Cuff must be correct size: Cover 2/3 of arm, middle of bladder over brachial artery, bladder width 40% of mid circumference of limb Can do venous stasis Must inflate/deflate quick (3mmHg/s) Can be affected by arrhythmia External pressure on cuff can affect Frequent measurement can cause ulna nerve palsy and petechial haemorrhage of skin
132
What is pulse oximetry?
Measure of how much haemoglobin in the artery is carrying oxygen %
133
What is beers law?
Amount of light absorbed is proportional to concentration of light absorbing substance - haemoglobin The more haem = more absorbed
134
What is lambert's law?
Amount of light absorbed is proportional to the length of the light pathway - size of artery Wider artery has same haem per unit area but more overall area so therefore more light is absorbed
135
What are the LEDs used and there wavelengths and how does they relate to pulse oximetry?
Red - 660 nm Infrared - 940 nm Oxyhaemoglobin absorbs more IR than red Deoxyhaemoglobin absorbs more red than IR They absorb a different amount of light at different wavelengths Pulse ox works out sats by comparing how much red/IR is absorbed as a ratio
136
How does the pulse ox distinguish arterial results from surrounding tissue?
Surrounding tissue will also absorb some light Arteries are pulsatile so any changing absorbable just be from an artery as path length changes with each pulse (lambert) Unchanging absorption must be from surrounding tissue
137
What is the plethysmographic waveform?
Graphical form of pulsatile change in absorbance | Shows signal quality
138
How does the pulse ox account for ambient light?
Detector reads red, IR and ambient light Pulse ox rapidly switches LEDs on/off in specific sequence (100/s) Red on: detect red and ambient Red off, IR on: detect IR and ambient Both off: detect ambient only which can then be subtracted
139
What are some problems with pulse oximetry?
``` Movement Incorrect placement Too much ambient light Electromagnetic interference - diathermy Poor perfusion affects pulsation Nail polish, IV dyes and some drugs interfere with wavelength Carbon monoxide joins Hb and detected as oxyHb Below 70% not accurate Change site 2 hourly - pressure sore Venous pulsation eg valsalva ```
140
What are the generals steps to a pulse ox measurement?
Detector detects light from LED Ratio of red to IR calculated Pulsatile vs non-pulsatile Flicking on/off to remove ambient
141
What is a capnograph?
A device that records and displays waveform and value of end of expiration
142
What is a capnogram?
Graphical plot of carbon dioxide partial pressure or percentage vs time
143
What is a capnometer?
A device that shows numerical concentration without a waveform
144
How does end tidal carbon dioxide analysis work?
CO2 absorbs IR Amount absorbed is related to amount of CO2 in sample chamber Remaining IR goes to photodetector which produces heat Heat is measured by a temp sensor and the temp is inversely proportional to amount of CO2 in sample chamber Light also passes reference chamber of room air to compare RR measured from rise/fall
145
Describe a side stream analyser?
1.2mm ID tube samples gas at a constant rate of 150-200ml/min Tube connects to adaptor near pt and delivers to sample chamber Teflon so impermeable to CO2 and unreactive to agents Moisture trap and exhaust allows humid gas to be vented or returned Tube needs to be close as possible Time delays
146
What is a main stream analyser?
``` Sample chamber within patient gas stream High dead space Heated to 41 degrees to prevent condensation No time delay Can't measure other gases Only with intubated patients No gas removed from system ```
147
Compare side stream and main stream analyser.
Side: time delay, moisture trap, sample other gases, removes gas - return, leak risk, need calibration, use on non-intubated Main: no time delay, heat chamber, doesn't remove gas, dead space, can't measure others, can't use on non-intubated, no calibration
148
What are cardiogenic oscillations?
If sample line aspirates gas due to prolonged pause or expiration Ripples appear on the trace during alveolar plateau in sync with the heart beat Smoothed by high lung volume and peep
149
How is oxygen analysed?
Measure of FiO2 | Galvanic, polarographic and paramagnetic method
150
How does the paramagnetic analyser work?
O2 attracted to magnetic field The O2 is attracted and agitated leading to a change in pressure in both chambers The pressure difference is proportional to pp difference between the chambers
151
What are the benefits of the paramagnetic analyser?
``` Very accurate Most common Most rapid and can be breath-by-breath Continuous High and low alarms Displays pp and % (Pauling) Needs water trap - affected by vapour ```
152
What are the components of nitrous and agent analyser?
``` Sample tube Sample chamber IR light source Optical filters Photodetector ```
153
What is the mechanism of the nitrous and agent analyser?
Sample enters chamber and exposed to IR Photodetector measures the light reaching it across correct wavelength Absorption of IR proportional to concentration Electrical signal analysed and process Optical filters used to select correct wavelength
154
How are shapes used to identify agents in the analyser?
Can measure up to 3 agents 5 sensors produce spectral shape which represents spectral signal of agent in sample This is compared with spectral shapes stored in memory to ID Amplitude of shape is inversely proportional to the amount of agent Optical filter used to filter desirable wavelengths
155
How do piezoelectric crystals work in analysis?
Can measure agent concentration Lipophilic coated crystal undergoes changes in natural resonant frequency when exposed to lipid soluble agents Change in frequency proportional to pp of agent Lacks agent specificity Sensitive to vapour
156
What is mass spectrometry?
Breath-to-breath Charge particles of sample with beam and then separate components into a spectrum according to their mass to charge ratio Done in high vacuum avoids interference Abundance of ions at certain mass:charge ratios is determined and relates to composition of mixture Magnet used to separate ion beam into spectrum (Sample hit with high energy electrons and exposed to MF to sort ions) High expense
157
What systems can measure oxygen?
``` Paramagnetic Polarographic Galvanic Mass spec Raman spec ```
158
What systems can measure CO2?
IR Mass spec Raman spec
159
What systems can measure agent concentration?
IR Mass spec Raman spec Piezoelectric
160
What is a pneumotachograph?
Measure gas flow and calculates flow rate, TV and MV Component: tube with fixed resistance from a bundle of parallel tubes, 2 P transducers either side Sense a change of P across resistance (Gas flow through is laminar) Change in P proportional to flow rate TV summated over minute - MV Bi directional Water vapour at resistor affects accuracy - hearing tubes help
161
What factors affect pneumotachograph readings?
``` Location Gas composition Gas temperature Humidity Dead space ```
162
What is a peripheral nerve stimulator for?
Monitor transmission across neuromuscular junction | Establishes depth, reversal and type of block
163
What is EMG and NMT?
Electromyography - electrical activity Neuromuscular transmitter - transmission across junction
164
What nerves can be stimulated?
Ulna Common peroneal- at fibula neck Posterior tibial - at ankle Facial
165
What is the tetanic stimulation mode?
A tetanus of 50-100Hz is used to detect residual block | Fade will be apparent
166
What is TOF mode?
``` Assess degree of block Ratio of 4th to 1st twitch 4x 2Hz twitches over 2s Fade noticed first, then lose 4th then 3rd etc twitch 2 twitches to reverse >3 absent for ideal abdo surgery ```
167
What is the double burst function?
More accurate assessment of residual block 2x short 50Hz tetanus Each twitch comprises of 2-3 square wave impulses
168
What safety considerations should be thought of for nerve stimulators?
Awake can hurt | Hand muscles small in comparison to diaphragm therefore result at hand doesn't reflect true depth of diaphragm block
169
What is BIS?
Bispectral index Monitor electrical activity and sedation of the brain Assess the risk of awareness Allows titration of hypnotics based on individual needs Measures hypnotic component but less sensitive to analgesic components
170
What are the components of BIS?
Display: BIS value, facial EMG, eeg suppression, signal quality index Forehead sensor with 4 electrodes and a smart chip Small tines in electrode part outer skin layers and hydrogel to make contact Reduces impedance and optimise Flexible design fits most
171
How does BIS work?
BIS is a statistic analysis, empirical method that quantifies the level of synchronisation of underlying frequencies Value derived mathematically using info from EEG, frequency and BIS info Produces linear scale 1-100
172
What are the values for BIS?
``` 100 - awake 0 - electrical silence 65 - 85 sedation 40 - 60 GA 60 return of conscious state ```
173
What are some safety features of BIS?
Inaccurate at low temperatures Ketamine is dissociative so cannot monitor Insufficient data for use with neuro disease Interference with diathermy and EMG
174
What is entropy?
Measure anaesthetic depth by amount of disorder of eeg signal Forehead sensors Calculates the frequency of voltages for each time sample and converts into normalised spectrum SE: 0-91; RE: 0-100
175
What is state and response entropy?
State: calculated from low frequency range corresponding to EEG Response: calculated from high frequencies and EMG from frontal muscle
176
What are the components of invasive arterial monitoring?
In-dwelling Teflon cannula Has parallel walls to reduce effect of flow to distal limb Column of NaCl (hep) at 300mmHg in flushing device Connects to transducer which connects to amp and oscilloscope Strain gauge variable resistor used Thin membrane diaphragm is interface between fluid and transducer Low compliance tubing so doesn't move with each pulse
177
How does invasive arterial monitoring work?
Transducer changes R in response to change in P NaCl column goes up/down with arterial pulse causing movement of diaphragm Transducer connects to Wheatstone bridge Changes in R and I are converted and displayed as systolic, diastolic, MAP 3-4ml/Hr flush cannula to prevent back flow and clotting
178
How does a Wheatstone bride in the arterial transducer work?
Electrical circuit for comparison of resistors Galvanometer, 4 resistors in 2 parallel branches 2 known R, 1 Variable and 1 Unknown The ratio of the 2 branches are compared and a current will flow through the galvanometer if there is an imbalance and therefore a reading
179
Draw the waves for an optimal, under and over damped pressure wave and for a square wave test.
See notes
180
What are some safety features of arterial monitors?
Transducer should be at RA level as reference point; every 10cm out gives a 7.5mmHg error Haematoma, infection, nerve damage, thrombosis, ischemia, bleeding More peripheral arteries are narrower and less compliant therefore increased amplitude Narrow/bifurcate arteries impede flow so backward reflect of P wave Drug injection = occlusion, gangrene Re-zeroing to reduce baseline drift
181
Why is zeroing an arterial line important?
Eliminates atmospheric pressure effects | Ensure monitor indicates zero in the absence of applied pressure therefore eliminating drift
182
How is a CVC placed?
Jugular, subclavian or basilic vein Sterile with landmark or ultrasound guidance Seldinger technique J-shaped soft tip wire inserted through into needle. Tip lessens trauma. Needle removed. Small incision in skin. Dilate. Railroad catheter over wire then remove wire. Aspirate and flush each port. Secure and check with X-ray
183
What is a PICC line?
Inserted via ACF Prolonged drug therapy which may be vein irritant Several months
184
What is a Hickman line?
Inserted via subclavian vein with proximal end tunnelled under the skin. Cuffed to hold in place and reduce infection Long term therapy Months - years
185
What are some safety features of a CVC?
``` Too far in - arrhythmia Blocked, failure Pneumothorax Infection, bleeding, nerve damage Air embolism Haematoma Tracheal puncture ```
186
What are ways to reduce CVC infection rate?
``` Sterile method Subclavian site Ultrasound guide to reduce number of attempts Minimal number of ports Remove ASAP AB coated lines Sterile, clear dressings ```
187
What are the components of a PA catheter?
``` 5-8G Upto 5 ports Distal lumen is PA Proximal lumen in RA Other proximals can infuse drugs Another lumen houses wires for thermistor - 3.7cm from tip Lumen to inflate balloon up to 1.5ml air Can be inflated to float with blood or when wanted PCWP Lumen to connect to P transducer Some can measure mixed venous O2 sats ```
188
What is the mechanism of the PA catheter?
Flush lines, test balloon Connect to P transducer Partially inflate balloon to get to RA Watch waveform! Fully inflate balloon to get tip to pulmonary artery branch where it will wedge. This measurement reflects Left atrial filling pressure Deflate balloon so catheter floats back to PA. Keep deflated until PCWP wanted
189
How does thermodilution work?
10ml of cold injectate administered upstream. Thermistor in PA measures change in temperature of blood downstream and a temperature time curve is created. This can then calculate CO. Volume of injectate must be accurate and quick. Mean of 3 readings used. Low blood = high temperature change High blood = low temperature change
190
What are the safety concerns of a PA catheter?
``` Arrhythmia VT Heart block Valve damage Perforate PA Don't advance >10cm without a change in waveform Thrombosis, infection, pulmonary infarction Whip artifacts ```
191
What is the LiDCOrapid?
CO monitor uses arterial waveform analysis to generate cardiac output Assess fluid and inotrope affects Algorithms used Can assess SV and its response to fluid challenges
192
How does a thermistor work?
A temperature dependant semi conductor and a Wheatstone bridge A change in temp = change in R Small and cheap
193
How does an IR tympanic temperature probe work?
Small probe inserted into external auditory meatus Detected by a series of thermocouples (thermopile) Detector receives IR from tympanic membrane IR signal converted to electrical signal Must be accurately timed False low; wax
194
How does a thermocouple work?
2 strips of different metals in contact from both ends and galvanometer One junction for measure and one for reference Metals expand and contract to different degrees with changing temp which produces a voltage compared with reference Generate a voltage which is temperature dependant Accurate to 0.1
195
What are the measurable sites for temperature?
``` Rectal Oesophageal (core) Tympanic (core) Bladder (accurate if output normal) Skin Axillary ```
196
What is the oesophageal Doppler?
Quick estimate of CO Probe in Oesophagus Close to aorta; minimal interference Adequate sedation needed
197
How does an oesophageal Doppler work?
Principle: high frequency when approach and low when travelling away Ultrasound waves encounter moving RBC. Frequency determines flow Probe inserted in mouth with bevel facing up at back of throat Probe rotated and slowly pulled back Position: 5-6 thoracic vertebrae adjacent to aorta
198
What is the mechanism of action of a hot water bath?
Water heated 45-60 degrees Dry/cold gases enter container where some pass close to surface of water = max saturation Container has ^ SA for vaporisation which ensures gas is fully saturated Tubing has poor thermal insulation causing a drop in temp By ^ temp > body temp it's possible to deliver it at 37 degrees, fully saturated Temp measured at pt end and feedback to control water temp
199
What are the safety features of hot water bath?
``` Need electricity Potential shock/burn 2nd thermostat if first malfunctions Water trap should be lower than pt to prevent flooding of airway by condensed water Water may be colonised Microbe risk drops with higher temp but burns risk then increases Large, expensive Leak risk ```
200
Define relative humidity.
Ratio of the amount of water vapour in the air at a specific temp compared to the maximum it could hold
201
Define absolute humidity.
Measure of the amount of water vapour in the air. Measured as partial pressure g H2O vapour/ cm3
202
What is the minimum humidification outcome for an HME?
30 degrees | 30gm-3
203
What are some comments regarding the position of the filter in the system?
Should be higher than lung level and in a vertical position to reduce chance of a complete block. A block on pt side stops exp but allows insp. Should be after lime to prevent drying and therefore not encourage compound A/monoxide production
204
What are the effects from theatre pollution?
``` Abortion Low fertility Haematological malignancy Renal/liver dysfunction Low mental performance ```
205
Describe the collection system for AGSS?
Gather from APL or from ventilator exhaust valve 30/19mm connection This mustn't cause R to expiration
206
What are safety features of the unidirectional valves?
Clear housing Hydrophobic Sit on knife edge to avoid sticking
207
How does colorimetric CO2 work?
It contains paper which changes colour in the presence of CO2 based on pH
208
What is the conversion between kPa and water?
1 kPa = 10 cmH20
209
What is a port-a-Cath?
SC port attached to a central catheter Surgically placed Prolonged intermittent therapy Months - years
210
What is a CVC?
Resuscitation or pressure monitoring | Up to 14 days
211
What are the indications for central lines?
``` Chemo Long term AB TPN Haemodialysis Repeated transfusions or samples Peripheral irritant ```
212
What are the correct DLT sizes?
41/39 male | 37 female

Anaesthesia (8 decks)

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