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Anaesthesiology > Equipment In Anaesthesia: Part 1 > Flashcards

Equipment In Anaesthesia: Part 1 Flashcards

Information from this deck is from the book Equipment in Anaesthesia in Critical Care: A complete guide for the FRCA.

1
Q

What is a VIE

A

Vacuum Insulated Evaporator
Storage tank for liquid oxygen
Keep contents below 160 Celsius
Provide piped O2 to most hospitals

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2
Q

Advantages of a VIE

A
  1. Storing liquid oxygen is highly space efficient
  2. Liquid oxygen is stored at much lower pressures than gas at room temperature
  3. No power source required
  4. Cheaper option for storage and delivery
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3
Q

Disadvantages of a VIE

A
  1. Initial equipment costs higher than manifold
  2. Backup cylinder manifold or VIE required in case of interruption
  3. If demand is not continuous, oxygen will be vented and lost.
  4. SAFETY: VIE must be kept outside due to fire risk.
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4
Q

What is the pressure inside a VIE, and what is the relevance?

A

7 Bar / 700kPA
It is the saturated vapour pressure of O2 at -160C

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5
Q

What happens to oxygen in a VIE before entering the hospital pipeline

A
  1. Superheater brings to ambient temperature
  2. Pressure regulator brings to 400kPA
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6
Q

Two ways of measuring the oxygen content in a VIE

A
  1. Mass: weighing on a tripod scale. Subtract tare weight from measured weight.
  2. Difference between vapour pressure at the top of VIE and the bottom of the liquid Oxygen. Calculate height of column and deduce volume from cross-sectional area.
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7
Q

What is a cylinder manifold

A

A pipe with several openings connected to cylinders;
Primary supply for small hospitals OR backup supply for larger hospitals.

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8
Q

Which gases are typically supplied by a cylinder manifold

A

Oxygen
Nitrous Oxide
Entonox

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9
Q

Size cylinders used in a manifold

A

J, L

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10
Q

Advantages of cylinder manifold

A
  1. Simple and cheap
  2. Effective backup
  3. Alarm system avoids running empty
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11
Q

Disadvantage of cylinder manifold

A
  1. Limited capacity compared to VIE
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12
Q

Safety considerations for a cylinder manifold

A
  1. Keep in a well-ventilated building separate from main building, due to fire and explosion risk;
  2. Main cylinder store should be in a separate room
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13
Q

Materials used for gas cylinders

A

a. Chromium molybdenum steel
b. Aluminium

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14
Q

Information found on a gas cylinder

A
  1. Label: gas, chemical formula, cylinder size, batch number, maximum safe operating pressure, expiry date, notes on storage, handling, and hazards;
    Plastic disk: date cylinder was last tested
    Valve block: testing pressure
    Cylinder itself (engraved): test pressure, dates tested, tare weight, serial number
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15
Q

What are various cylinder sizes used for:
CD
E
J

A

CD: transporting patients
E: attached to anaesthetic machine
J: cylinder manifold

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16
Q

Size CD tank:
- oxygen volume at 137 Bar, 15C
- water capacity
- tare weight

A
  • 460 litres
  • 2 litres
  • 3 kg
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17
Q

Size E tank:
- oxygen volume at 137 Bar, 15C
- water capacity
- tare weight

A
  • 680 litres
  • 4.7 litres
  • 5.4 kg
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18
Q

Size J tank:
- oxygen volume at 137 Bar, 15C
- water capacity
- tare weight

A
  • 6800 litres
  • 47 litres
  • 69 kg
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19
Q

Define critical temperature of a gas

A

Temperature at which the gas turns from liquid into gas,
above the temp it is impossible to compress it into liquid

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20
Q

Critical temperature of:
1. oxygen
2. nitrous oxide

A
  1. -116C
  2. 36.5C
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21
Q

Advantages of gas cylinders

A
  1. small cylinders are portable
  2. variety of connectors exist
  3. refillable, reusable
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22
Q

Disadvantages of gas cylinders

A
  1. big cylinders are heavy to transport
  2. not all connectors present on all cylinders
  3. amount of gas limited by volume of cylinder
  4. no alarm if gas runs out
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23
Q

Safety considerations for gas cylinders

A
  1. must be tested every 5-10 years
  2. filling ratio used (in UK: 0.75 at 15.5C; in warmer climates: 0.67)
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24
Q

Define filling ratio of gas cylinders;
explain its purpose

A

Weight of the liquid in a full cylinder, divided by the weight of water that would completely fill the same cylinder;
allows for pressure increases if temperature rises, without the risk of explosion.

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25
Q

True/False:
A filling ratio of 0.75 is exactly the same as the cylinder being 75% full

A

FALSE

Reason: differences between density of water and cylinder contents

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26
Q

Sources of production of medical grade air

A
  1. air compressor
  2. cylinder banks (smaller hospitals)
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27
Q

Pressures and respective uses of medical air

A

400kPa (4Bar): anaesthetic equipment/ventilators;
700kPa (7Bar): powering surgical equipment

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28
Q

Advantages of air compressor

A

More cost-effective for larger hospitals than a cylinder bank

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29
Q

Disadvantages of air compressor

A

Higher initial costs than cylinder bank

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30
Q

Safety considerations: air compressor

A
  1. Risk of contamination by air pollution: must be carefully situated and regularly inspected
  2. Risk of oil mist contamination
  3. Non-interchangeable Schrader valves to prevent accidental connection of high-pressure air to anaesthetic machine
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31
Q

Function: oxygen concentrator

A

Produce concentrated oxygen from air;
Inlet: 78% Nitrogen, 21% Oxygen, 1% Argon, variable water vapour;
Outlet: 95% Oxygen, 5% Argon

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32
Q

What is a zeolite

A

Aluminosilicate;
Forms lattice structure in oxygen concentrator;
molecular sieve;
filters specific molecules while letting others through.

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33
Q

Oxygen concentrator: advantages

A
  1. cheap and reliable for home oxygen
  2. reduce need for commercial deliveries of oxygen
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34
Q

Oxygen concentrator: disadvantages

A
  1. Argon accumulates if used at low flows on anaesthetic circle system (leads to hypoxic mixture)
  2. requires power supply
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35
Q

Oxygen concentrator: safety considerations

A

Explosion hazard; patient must give up smoking

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36
Q

Safety features of piped medical gas supply

A
  1. colour-coded hoses and sockets
  2. labelled hose and outlet
  3. schrader probes/connections
  4. diameter index collar connection
  5. non-interchangeable screw thread for connection to anaesthetic machine
  6. emergency shutoff valves
37
Q

Minimum physical paremeter requirements for a medical vacuum system

A

Pressure: -400mmHg/-53kPa
Flow: 40l/min
i.e: high pressure, low flow

38
Q

Medical vacuum system: advantages

A
  1. essential for safe anaesthesia
  2. centralised vacuum supplies are highly reliable
  3. collection systems are cheap, simple, disposable
39
Q

Medical vacuum system: disadvantage

A
  1. disconnections and leaks are common
  2. portable units battery life limit use
40
Q

Use of scavenging systems

A

reduce environmental anaesthetic gas concentrations by collecting waste gases and venting them outside the building.

41
Q

Describe active and passive scavenging systems

A

Active: pump generates negative pressure. Requires open receiving system to prevent transfer of negative pressure to patient.
Passive: uses positive pressure generated by patient’s expiration to transmit gas to atmosphere via closed receiving system

42
Q

Components of a scavenging system

A
  1. Collecting system (connected to APL)
  2. Transfer system (corrugated hose)
  3. Receiving system (active or passive)
  4. Disposal system (modern systems are high flow, low pressure)
43
Q

How many times per hour should the air in operating theatres be changed

A

At least 20 times

44
Q

What is a Cardiff Aldasorber

A

A simple passive device: canister containing activated charcoal, which absorbs volatile agents.
Used in resource-poor locations.
If heated, agents are vented to atmosphere.

45
Q

Factors that affect the oxygen delivery by a variable performance device

A
  1. mask volume
  2. respiratory dynamics of patient
  3. seal of the mask
46
Q

Examples of fixed performance oxygen devices

A
  1. venturi mask
  2. high flow nasal cannulae
47
Q

Nasal cannula: advantages

A
  1. simple and cheap
  2. patients can speak, eat, and drink
  3. good patient compliance
48
Q

Nasal cannula: disadvantages

A
  1. variable FiO2
  2. drying of nasal mucosa limits flow
49
Q

Oxygen masks: advantages

A
  1. simple, cheap, widely available
  2. easy to vary oxygen delivered, but not to precise concentrations
  3. simplest way to deliver high concentrations of oxygen
50
Q

Oxygen masks: disadvantages

A
  1. variable performance device
    - precise FiO2 unknown, not suitable for calculations
  2. rebreathing of exhaled CO2 is possible
51
Q

True/False:
A Venturi mask can deliver higher oxygen concentrations than its labelling

A

False

52
Q

State the Bernoulli principle

A

in order to maintain a constant FLOW,
a fluid must increase its VELOCITY
as it flows through a CONSTRICTION

53
Q

State the first law of thermodynamics

A

Energy cannot be created or destroyed, only transferred

54
Q

True/False:
The apertures of a 60% Venturi mask are smaller than the apertures of a 24% Venturi mask

A

TRUE

55
Q

Venturi mask: advantages

A
  1. simple, lightweight
  2. delivers a specific and consistent FiO2 under normal circumstances
  3. Patient’s respiratory rate and pattern do not alter the FiO2
56
Q

Venturi masks: disadvantages

A
  1. risk of under-delivery if flow set too low
  2. high flows can dry airways
  3. less accurate at higher FiO2
  4. behaves like a variable performance device if patient’s inspiratory flow requirement exceeds the O2 flow.
  5. droplets from humidifiers may occlude the narrow oxygen inlet
57
Q

Nasal high-flow devices:
1. max flow deliverable
2. positive airway pressure provided

A
  1. 60l/min
  2. 5 cmH2O
58
Q

Nasal high-flow: advantages

A
  1. better tolerated by some
  2. fixed performance, permitting up to 100% FiO2
  3. gas is warmed and humidified
  4. low level positive airway pressure is possible
59
Q

Nasal high-flow: disadvantages

A
  1. little peer-reviewed evidence so far
  2. more expensive
  3. not widely available
60
Q

Sealing face masks: advantages

A
  1. Allows up to 100% FiO2
  2. Simplest way of applying positive pressure ventilation
61
Q

Sealing face masks: disadvantages

A
  1. seal may be difficult to achieve
  2. volume within mask is dead space
  3. patients may be claustrophobic
  4. masks can cause pressure injuries: skin breakdown, trigeminal nerve injury
62
Q

Guedel airway: disadvantages

A
  1. poorly tolerated by semiconscious patients
  2. may cause bleeding and oropharyngeal injuries
  3. incorrect sizing may cause obstruction
63
Q

Nasopharyngeal airway: advantages

A
  1. tolerated in semiconscious patients
  2. provides a conduit for suctioning
64
Q

Nasal airways: safety risks

A
  1. coagulation disorders
  2. basal skull fractures
65
Q

LMA: advantages

A
  1. neuromuscular blocking drugs not required
  2. insertions easier than intubation
  3. minimal haemodynamic response cf intubation
  4. emergence is smooth
  5. part of difficult airway algorithm
66
Q

LMA: disadvantages

A
  1. difficulty obtaining a seal in some patients
  2. not a definitive airway - risk of aspiration
  3. may cause laryngospasm
  4. seals to low airway pressure: 20cmH2O
  5. position less stable in edentulous patients
67
Q

Which IV induction agent is better for use with LMA, and why

A

Propofol;
inhibits airways reflexes to a much greater degree than thiopentone

68
Q

Bougie: uses

A
  1. facilitate tracheal intubation
  2. airway exchange
  3. during emergency surgical cricothyroidotomy
69
Q

Bougie: advantages

A
  1. narrow diameter: superior visualisation of airway anatomy
  2. angled tip to identify tracheal rings
  3. some shape retention
70
Q

Bougie: disadvantages

A

Size 4 ETT minimum

71
Q

What useful feature is found in an airway exchange catheter

A

it has an adapter for connection to a standard 15mm connector or jet ventilator. Allows for oxygenation/ventilation during exhange.

72
Q

What is the correct use for a left-handed laryngoscope blade

A

In patients with large RIGHT SIDED facial deformities

73
Q

What is the functional difference between curved and straight laryngoscope blades

A

Curved blades indirectly lift the epiglottis via pressure on the hyoepiglottic ligament;
Straight blades are placed directly over the epiglottis to lift it directly.

74
Q

Adjustments to laryngoscopes for patients with large breasts

A
  1. blade mounted on the handle at 135 degrees instead of 90 degrees
  2. stubby handle
  3. indirect laryngoscopes
75
Q

Rigid indirect laryngoscopes: advantages

A
  1. convert difficult intubations to easy
  2. reduced lifting force required, therefore reduced haemodynamic response to intubation
  3. minimal cervical spine movement required
  4. reduced airway trauma
  5. easier to teach
76
Q

Rigid indirect laryngoscopes: disadvantages

A
  1. difficulty passing tube despite excellent views
  2. better mouth opening required than for fibreoptic intubation
  3. expensive
  4. blood and secretions significantly impair the view.
77
Q

Fibreoptic endoscopes for intubation: uses

A
  1. awake or asleep intubation in difficult airways
  2. confirm position of ETT, especially in double lumen tubes
  3. placement of bronchial blockers
  4. guiding percutaneous tracheostomy
  5. suctioning, pulmonary toilet
  6. diagnosis of upper airway pathology
78
Q

Define: critical angle of incidence

A

The angle of incidence that causes the angle of refraction to equal 90 degrees

79
Q

State Snell’s Law

A

When light moves from a material with a higher index of refraction to a material with a lower index of refraction, it is bent away from the normal.

80
Q

Define total internal reflection

A

Occurs when the angle of refraction is 90 degrees or greater, and is reflected back into the original material. No more light enters the new material.

81
Q

What should be the inflation pressure of the cuff of an ETT

A

20-30cmH2O

82
Q

What are modern ETTs made of

A

clear polyvinyl chloride

83
Q

Use of laser ETT

A

Laser airway surgery, to resist melting and combustion of tube

84
Q

True/False:
Laser tubes are not necessary for laser surgery away from the airway

A

True

85
Q

Safety features of laser ETT

A
  1. Metal exterior with a matt surface, defocuses reflected beams to protect healthy tissue
  2. double cuff to maintain seal if the first one is perforated
86
Q

What is a microlaryngeal tube

A

Size 4-6mm ETT with longer lengths that can be used in adult patients.

87
Q

Uses of microlaryngeal tubes

A
  1. microlaryngeal surgery
  2. patients with pathologically narrow trachea or larynx.
88
Q

Microlaryngeal tubes: disadvantages

A
  1. narrow lumen may become blocked
  2. high resistance precludes spontaneous ventilation
  3. surgical access still impaired compared to jet ventilation

Anaesthesiology (12 decks)

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