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CPS > Breathing systems > Flashcards

Breathing systems Flashcards

1
Q

What are the functions of a breathing system?

A
  • Supply oxygen
  • Supply anaesthetic agent
  • remove CO2
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2
Q

What are the 2 types of breathing circuit?

A
  • Re-breathing

- Non-rebreathing

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3
Q

Describe the main features of non-rebreathing circuits

A
  • High flow rates used to flush out CO2
  • Expensive
  • More oxygen, nitrous oxide and inhalant used
  • Cannot be used for large animals
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4
Q

Name the main types of non-rebreathing circuit

A
  • Magill
  • Lack (and mini Lack)
  • Bain (and mini Bain)
  • T piece
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5
Q

Describe the Magill breathing circuit

A
  • Valve near patient
  • Bag at opposite end
  • Circuit factor 1
  • Should no longer be used
  • Used in large dogs over 10kg
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6
Q

What are the disadvantages of the Magill breathing circuit?

A
  • Heavy end near patient due to valve, risk of pulling ET tube out of the patient’s mouth
  • Inefficient for IPPV
  • Risk of breathing own CO2
  • Alveolar gas is vented and dead space gas is rebreathed
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7
Q

What are the advantages of the Magill breathing circuit?

A

Efficient for spontaneous breathing

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8
Q

Describe the Lack breathing circuit

A
  • Bag and valve at machine end
  • Parallel running tubes
  • Green tube is fresh gas
  • Circuit factor 1
  • Only for animals >10kg spontaneously breathing
  • Inefficient for IPPV
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9
Q

Describe the mini Lack breathing circuit

A
  • Smooth bore tubing
  • Lightweight valve
  • Minimal resistance
  • Circuit factor 1
  • Animals 2-10kg
  • Not suitable for long term IPPV unless fresh gas flow increased to 600ml/kg/min
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10
Q

Describe the Bain and mini Bain breathing circuits

A
  • Smaller tube within another tube (green is inner, supplies fresh gas)
  • Circuit factor 2.5
  • High flow rates
  • Good for IPPV
  • Bain can be used on animals 7-20kg
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11
Q

Describe the T piece breathing circuit

A
  • No valves
  • Low resistance
  • Used for animals <10kg
  • High flow rates
  • Circuit factor 2.5
  • Good for IPPV
  • Long green tube, smaller bore
  • Shorter white tube with bag ad valve at end
  • Valve at machine end
  • Human pediatric versions often used with teddy on bag
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12
Q

Explain how fresh gas flow rate is calculated for non-rebreathing systems

A
  • Assume minute volume is approx 0.25L/kg

- Flow rate (L/min) = circuit factor x body weight x 0.25

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13
Q

What factors may affect the fresh gas flow rate required?

A
  • Pain
  • Pyrexia
  • Depth of anaesthesia
  • Size of animal
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14
Q

In what proportion of fresh gas flow should nitrous oxide be given?

A
  • Should be given as 2/3rds of total fresh gas
  • 1/3rd oxygen
  • I.e. 5L/min total FGF, give 3L nitrous oxide, 2L oxygen
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15
Q

What are the different types of rebreathing circuits?

A
  • To and Fro

- Circle

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16
Q

Describe To and Fro circuits

A
  • Outdated
  • Soda lime between patient and bag
  • Can lead to soda lime dust inhalation
  • CO2 channeling over soda lime so is not absorbed
  • Dead space increases with time
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17
Q

Describe the benefits of circle circuits

A
  • Efficient
  • Warms and humidifies gas
  • Less pollutant
  • Easy to use and perform IPPV
  • Lower fresh gas flows, less oxygen, less inhalant required
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18
Q

Describe the layout of circle circuits

A
  • Fresh gas flow enters from commo gas outlet of anaesthetic machine
  • Flows through one way valve to patient through inspiratory tube
  • Through Y-piece to patient
  • From patient through expiratory tube, through one way valve on expiratory limb
  • In and out of reservoir bag
  • Through soda lime cannister and back to patient mixed with fresh gas
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19
Q

What is the main difference between rebreathing and non-rebreathing circuits?

A

Rebreathing circuits have absorbent (most commonly soda lime) in circuit

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20
Q

Describe absorbents in rebreathing circuits

A
  • Usually calcium hydroxide (soda lime) and barium hydroxide lime
  • Incorporate indicators to show activity
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21
Q

Give the chemical reaction that occurs in soda lime

A

2H2CO3 + 2NaOH + Ca(OH)2 -> CaCO3 + Na2CO3 + 4H2O + heat

H2O+CO2 -> H2CO3

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22
Q

Describe the valves used in rebreathing circuits

A
  • Pressure generated by patient’s breathing, causes disc to move, gas passes in one direction only
  • Transparent dome allows visualisation of movement
  • Valves/discs can be made of deformable rubber or mica or plastic (light materials)
  • Must be checked as can get stuck
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23
Q

What volume of air must be in the breathing bag on a circuit?

A
  • Must be greater than the patient’s inspiratory capacity

- Estimated to be 30ml/kg

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24
Q

What volume should be absorber cannister be?

A
  • At least double that of the tidal volume of the patient in order to optimise efficiency
  • Soda lime contains 50-70% air around the granules
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25
Q

What are the 2 types of fresh gas flows that can be used with circle circuits?

A
  • Closed

- Semi-closed/open

26
Q

Describe the closed fresh gas flow system

A
  • O2 consumption (m/min)= 10xbodyweight^0.75
  • Only supplying enough oxygen for the patient to stay alive
  • E.g. for a 20kg dog, require 95ml/min of O2, only supply this amount
  • Requires FIO% monitor
  • Risky, not used
27
Q

Describe the semi-closed/open fresh gas flow system

A
  • O2 flow rate exceeds patient’s O2 consumption
  • Excess lost via pressure relief valve into scavenge
  • Initially have high flow rate, high vaporiser setting to raise concentration of anaesthetic in circuit
  • For maintenance, both are reduced
  • General rule: 2-3L/min for first 10-15 min, then 500-1L/min during maintenance
  • For large animals e.g. horses, 8-10L/min initially then reduce
28
Q

What are the advantages of lower fresh gas flow?

A
  • Less wastage
  • Cheaper (less inhalant and carrier gas used)
  • Less pollutant
  • Gases warmed and humidified
29
Q

Describe the steps required when changing inhalant concentration used during anaesthesia in an open circle system

A
  • Open valve
  • Increase fresh gas flow
  • Set to desired concentration
  • Expel old concentration using bag
  • Close valve but leave semi-open
  • Reduce FGF after 10-15mins to maintenance
30
Q

In what ratio is nitrous oxide used in circle systems?

A

50:50, but little benefit of using nitrous oxide, MAC is unachievably high

31
Q

What are the advantages of the HUmphrey ADE circle (combination) system?

A
  • Compact, robust, easy to clean
  • Versatile (2-100kg)
  • Positive End Expiratory Pressure Valve maintains positive pressure between breaths and stops collapse of alveoli in small patients
  • Excellent for IPPV
  • Metal is non-ferrous, can go close to MRI
32
Q

Describe induction chambers

A
  • Useful as removes need for stressful restraint of small animals
  • Scavenge from top or lid
  • Oxygen and volatile enter at bottom
  • removable clear partition may be available to accommodate all sizes
33
Q

What is IPPV?

A

Intermittent Positive Pressure Ventilation

34
Q

Describe how IPPV is performed

A
  • AMBU bag or bag on breathing system
  • AMBU bag is self inflating
  • Deliver room air or oxygenated air to patient where they are not doing this themselves by squeezing the bag
35
Q

When is IPPV required?

A

When the patient cannot ventilate itself in order to prevent hypoxaemia (and consequent hypoxia)

36
Q

Describe the anaesthetic machine safety check

A
  • Switch off flow control valves
  • Ensure cylinders are closed and fitted securely on hanger yolks
  • Press emergency O2 button until no gas flows from common gas outlet
  • Check flowmeters and pressure gauges read 0
  • Switch on oxygen cylinder slowly and check pressure gauge, replace if low
  • Switch on flowmeter and check smooth operation
  • Check emergency O2 flush (switch off, then test second cylinder if present)
  • Check N2O cylinder
  • Switch O2 to 2L/min, N2O to 4L/min, then switch off )2 - oxygen failure device should alarm
  • check vaporiser is connected, full of agent, smooth dial movement when gas off, no leaks
  • Check emergency overpressure valve and air intake valve if fitted
37
Q

How useful is the nitrous oxide pressure gauge at indicating volume remaining in cylinder?

A

Poor, as nitrous oxide is stored a liquid/vapour and so will always read as full until empty, as vapour is constantly replaced from the liquid reservoir

38
Q

What is the importance of the flow control valves (flowmeters) on an anaesthetic machine regarding the part of the machine?

A
  • Divides machine into 2 parts
  • High pressure circuit upstream of flowmeters
  • Low pressure circuit downstream of flow control valves
39
Q

How is flow into the low pressure system of an anaesthetic machine regulated?

A
  • Regulated by the operator

- Adjust flowmeter control valves

40
Q

What is the function of the pin index on anaesthetic machines?

A
  • Pin Index Safety System is a safeguard that prevents cylinder interchaging
  • each gas or combination of gases has its own particular pin pattern to prevent wrong placement of gases onto yokes
41
Q

Where is gas flow rate read from depending on the type of float in a flowmeter?

A
  • Read from middle of ball

- Top of bobbin/float

42
Q

How do hypoxia prevention devices on anaesthetic machines work?

A
  • Interface oxygen and nitrous oxide systems to ensure minimum of 25% oxygen at common gas outlet
  • But are not foolproof
43
Q

What is the purpose of interlock devices on anaesthetic machines?

A

Prevent concurrent use of more than one vaporiser

44
Q

What is a potential outcome of tipping of vaporisers?

A

Movement of liquid anaesthetic into the bypass chamber, leading to very high anaesthetic agent concentrations being released to the patient

45
Q

What are the ISO colours for oxygen, nitrous oxide, medical air, suction and CO2 cannisters?

A
  • Oxygen: white
  • NO2: light blue
  • Medical air: black and white
  • Suction: yellow
  • CO2: grey and green
46
Q

What causes turbulent flow in breathing systems?

A

Bends and changes in direction of the gas and increases the resistance further

47
Q

When should soda lime be exchanged?

A

When the indicator has changed colour in approx 2/3rd of the absorbent

48
Q

What are important considerations when using circle circuits for small patients?

A
  • Standard circle absorbers cannot be used in small patients because of dead space
  • Have small tidal volumes and not enough pressure to open the valves
  • Effective dead space of Y-piece is larger than it appears so smaller Y-pieces must be used
49
Q

What affects the rate of change of anaesthetic concentration?

A
  • Fresh gas flow rate

- High FGF rate will achieve equilibration must faster than if low FGF rate is used

50
Q

Describe the Humphrey ADE-circle system

A
  • Combines advantages Mapleson A (spontaneous breathing patients) , D and E (preferable for controlled ventilation and small patients) systems
  • Possibility of adding absorbent canister and converting into circle
51
Q

What are the advantages of passive scavenging systems?

A
  • Inexpensive to set up
  • Simple to operate
  • Charcoal cannisters are mobile
52
Q

What are the disadvantages of charcoal cannister scavenges?

A
  • Continuing cost of replacemeent
  • Can be refilled with fresh charcoal but is messy
  • Does not remove nitrous oxide
  • Heating cannister causes release of inhalational agents
53
Q

Describe a simple active scavenge

A
  • Reservoir made of plastic pipe 3” diameter, 2 feet long
  • Capped at both ends, needle valve at bottom
  • 2 holes drilled in top cap
  • 1 hole for hose from outlet of anaesthetic machine to be inserted
  • Other to allow passage of atmospheric air
  • Valve adjusted so air is slowly sucked into pipe when anaesthetic machine is in use, preventing waste gas escape into the atmosphere
54
Q

What is an advantage of a simple active scavenge?

A

Convenient in large hospitals/practices where many machines are in use in different locations

55
Q

What is a disadvantage of a simple active scavenge?

A

Vacuum system and pipe work is major expense and may need continual adjustment

56
Q

What is meant by ambulatory infusion?

A
  • Animal is freely moving without need for tether to connect with catheter
  • Normally only in large animals that can carry jackets with infusion pump and compound reservoir
57
Q

What is meant by an atraumatic procedure?

A

Minimal tissue injury caused during the procedure

58
Q

What is meant by biocompatibility?

A

Good toleration of implants by animal tissues after implantation

59
Q

What is a biofilm?

A

A coating which develops on implanted materials derived from the animal’s own tissue fluids and cells

60
Q

What is the friction coefficient?

A

The surface friction of a catheter, affects how easily a catheter can be inserted into a blood vessel

CPS (13 decks)

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