Breathing Systems


Breathing Systems

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  1. Breathing Systems

    Slide 1 - Breathing Systems

    • Lisa Angell RVN
  2. What are the purpose of breathing systems?

    Slide 2 - What are the purpose of breathing systems?

    • Breathing systems are interposed between an anaesthetic machine and a patient.
    • Purpose:
    • -> Deliver Oxygen and Anaesthetic agents from the anaesthetic machine to the patient
    • -> Remove CO2 exhaled by the patient
    • -> Provide a means of ventilating the lungs
    • -> Deliver waste gases to the scavenging system
  3. Components of breathing systems

    Slide 3 - Components of breathing systems

    • Breathing tubes (limbs)
    • -> Move gases to and from patients
    • -> Allow flexible positioning of the breathing system
    • -> To act as a reservoir
    • Reservoir bag (breathing bag)
    • -> Allows accumulation of gas during exhalation
    • -> To Act as a reservoir for inhalation
    • -> Anaesthetist can visualise breathing
    • -> Method of assisted ventilation
  4. Embedded Quizzes – Office MIX

    Slide 4 - Embedded Quizzes – Office MIX

  5. Fresh gas inlet

    Slide 5 - Fresh gas inlet

    • -> Connects to the common gas outlet on the anaesthetic machine allowing the flow of oxygen
    • Pressure Relief Valve (APL valve)
    • -> Limits the build up of pressure within the system
    • -> Releases waste gases
    • -> Allows a safe connection to a scavenging system
    • CO2 Absorbant (Soda lime)
    • -> To absorb carbon dioxide, thus allowing complete
    • rebreathing of exhaled gases
    • One way valves
    • -> Ensure gases flow the correct way through the breathing
    • system
    • -> Prevents mixing of fresh gas with CO2 rich gas
  6. UK general classifications of breathing systems

    Slide 6 - UK general classifications of breathing systems

    • Open:
    • The anaesthetic agent is vaporised from a swab held close to the airway, for example a jam jar ether system
    • Semi-open:
    • The anaesthetic agent is vaporised from a swab held over the airway, for example a Cox’s mask
    • Semi-closed:
    • The patient inhales gas from an anaesthetic machine. Expiratory gas is voided into the atmosphere. e.g the Magill system
    • Closed:
    • The system incorporates chemical absorption of carbon dioxide, for example the circle system
    • Mapleson classification. (explained later)
  7. Non rebreathing systems

    Slide 7 - Non rebreathing systems

    • Non rebreathing systems rely on high fresh gas flow rates based on multiples of minute volume to flush expired CO2 from the circuit so that it cannot be rebreathed in the next breath
    • Advantages
    • -> Low resistance – ideal for small animals and birds
    • -> Simple construction
    • -> Inexpensive
    • -> Soda lime not required
    • -> Circuit concentration of anaesthetic can be changed rapidly
    • Disadvantages
    • -> High flow rates
    • -> High volatile agent consumption rate
    • -> Expired moisture and heat lost as dry cold gases are delivered to patient
  8. Mapleson's classification of non-rebreathing circuits

    Slide 8 - Mapleson's classification of non-rebreathing circuits

    • In 1954 Mapleson divided five non-rebreathing circuits into functionally similar groups (A – E), on the basis of the fresh gas flow required to prevent rebreathing and the ease with which intermittent positive pressure ventilation may be performed.
    • The mapleson F circuit was added later by Willis et al 
  9. Mapleson A

    Slide 9 - Mapleson A

    • Known as the Magill attachment
    • Popularised by Sir Ivan Magill in the 1920’s
    • The Magill consists of a 3 way tube connected to...
    • F: the fresh gas outlet
    • B: Rebreathing Bag
    • R: Reservoir tube
    • V: APL valve
    • P: Patient connection
    • Can be used on patients weighing between 10kg and 40kg.
  10. Function during respiratory cycle

    Slide 10 - Function during respiratory cycle

    • Inspiration:
    • -> The valve closes and the patient inspires fresh gas from the reservoir tube
    • Expiration:
    • -> The patient expires into the reservoir tube
    • -> The bag fills and positive pressure opens the valve
    • Expiratory pause:
    • -> Fresh gas washes the reservoir tube and fills again
  11. Controlled ventilation?

    Slide 11 - Controlled ventilation?

    • The Magill is generally not suitable for performing IPPV as when the bag is squeezed, the gas tends to escape from the circuit via the expiratory valve, rather than inflating the lungs.
    • This can be avoided by closing the valve during each inspiration, but is highly inconvenient.
    • It can be reduced by partially closing the valve, but would require high flow rates to prevent rebreathing.
  12. Advantages

    Slide 12 - Advantages

    • Inexpensive
    • Generally lower flow rates (as long as not trying to provide IPPV!)
    • Disadvantages
    • The position of the valve close to the patients head may get in the way during some surgeries
    • Difficult to perform IPPV effectively
  13. The other Mapleson A

    Slide 13 - The other Mapleson A

    • The Lack Circuit
    • A co-axial modification of the Mapleson A system
    • Dr A Lack. Retired Salisbury anaesthetist
    • Consists of :
    • F: 4 way block attached to the fresh gas outlet
    • R: Reservoir tubing (connected to the block
    • P: Patient attachment
    • E: Inner exhaust tube
    • B: Breathing bag
    • V: APL valve
    • Can be used on patients weighing more than 10kg
  14. Function during respiratory cycle

    Slide 14 - Function during respiratory cycle

    • Inspiration:
    • -> The valve closes and the patient inspires fresh gas from the outer reservoir tube
    • Expiration:
    • -> The patient expires into the reservoir tube
    • -> The bag fills and positive pressure opens the valve
    • -> Expired gas escapes via the inner exhaust tube
    • Expiratory Pause:
    • -> Fresh gas washes the expired gas from reservoir tube, filling for next breath
  15. Controlled ventilation

    Slide 15 - Controlled ventilation

    • As for the Magill circuit
    • Although the position of the APL valve and the breathing bag makes short term IPPV easier
  16. Advantages

    Slide 16 - Advantages

    • Inexpensive
    • Location of the valve is more convenient for short term IPPV
    • Disadvantages
    • Not suitable for IPPV
    • In common with other co-axial systems, if the inner tubing becomes disconnected or breaks, the entire reservoir becomes dead space.
    • This can be avoided by using the parallel lack system in which the inner and outer tubes are replaced by conventional breathing tubing and a Y piece:
  17. Mapleson B

    Slide 17 - Mapleson B

    • The Mapleson B system features the fresh gas inlet near the patient, distal to the expiratory valve
    • The expiratory valve opens when pressure in the circuit increases, and a mixture of alveolar gas and fresh gas is discharged
    • During the next inspiration a mixture of alveolar gas and retained fresh gas is inspired. Rebreathing is avoided with fresh gas flow rates of greater than twice the minute volume of the patient.
    • This circuit is unsatisfactory for anaesthesia, but may be used in emergency resuscitation
  18. Mapleson C

    Slide 18 - Mapleson C

    • This circuit is also known as the Waters circuit without an absorber.
    • It is similar in construction to the Mapleson B, but the main tubing is shorter
    • A fresh gas flow equal to twice the minute volume is required to prevent rebreathing.
    • CO2 builds up slowly with this circuit.
    • This circuit is unsatisfactory for anaesthesia, but may be used in emergency resuscitation
  19. Mapleson D

    Slide 19 - Mapleson D

    • Bain Circuit
    • A co-axial modification of the basic T-Piece system
    • Developed to facilitate scavenging of anaesthetic gases
    • Consists of:
    • F: Tube to carry fresh gas which travels inside an outer reservoir tube
    • R: Reservoir tube
    • P: Patient connection
    • Suitable for patients over 10kg
  20. Function during respiratory cycle

    Slide 20 - Function during respiratory cycle

    • Inspiration:
    • -> The patient inspires fresh gas from the outer reservoir tube
    • Expiration:
    • -> The patient expires into the reservoir tube.
    • -> Although fresh gas is still flowing into the system at this time, it is wasted as it is contaminated by the expired gas
    • Expiratory pause:
    • -> Fresh gas from the inner tube washes the expired gas out of the reservoir tube filling it with fresh gas for the next inspiration
  21. Controlled ventilation?

    Slide 21 - Controlled ventilation?

    • Can be used for long term IPPV
  22. Advantages

    Slide 22 - Advantages

    • Inexpensive
    • Low dead Space
    • Low resistance to breathing
    • Scavenges well
    • Can be used for IPPV and attached to a ventilator
    • Disadvantages
    • High fresh gas flow required in larger animals
    • High volatile agent consumption
    • Is co-axial, Although a parallel Bain system may be used. The inner and outer tubes are replaced circle tubing and a y-piece (this arrangement is also used in the Humphrey ADE system.
  23. Mapleson E

    Slide 23 - Mapleson E

    • The Mapleson E is a modification of the Ayres T piece which was developed in 1937 by Philip Ayre. He was a Newcastle Anaesthetist
    • The circuit was developed for use in paediatric patients undergoing cleft palate repair or intracranial surgery.
    • Consists of a 3 way T tube whose limbs are connected to:
    • F: Fresh Gas Supply
    • R: Reservoir tubing
    • P: Patient connection
    • The T piece has minimal dead space, no valves and minimal resistance
    • Suitable for patients weighing less that 10 kg
  24. Function

    Slide 24 - Function

    • Same as Bain
    • Fresh gas is inspired from the reservoir tube
    • Patient expires into the reservoir tube
    • During expiratory pause, fresh gas washed expired gas from the reservoir tubing
  25. Controlled Ventilation?

    Slide 25 - Controlled Ventilation?

    • Same as Bain
    • IPPV may be performed by intermittently occluding the end of the reservoir tube
    • The T-Piece can be connected to a ventilator.
  26. Mapleson F

    Slide 26 - Mapleson F

    • Jackson Rees’ modification of the Ayres T piece connects a two ended bag to the expiratory limb of the circuit. Gas escapes via the tail end of the bag.
    • This allows respiratory movements to be seen more easily and permits IPPV if necessary.
  27. Advantages

    Slide 27 - Advantages

    • Compact
    • Inexpensive
    • No valves
    • Low Dead Space
    • Low resistance to breathing
    • Economical for controlled ventilation
    • Disadvantages
    • Some T-pieces can be heavy and difficult to keep connected to smaller patients
    • On the Jackson Rees’ the bag may get twisted and stop the patient breathing
    • IPPV on the Ayres T piece is tricky without a breathing bag, this method can lead to over inflation of the lungs
  28. Rebreathing systems

    Slide 28 - Rebreathing systems

    • In these systems, CO2 is removed from the system by using an absorbing compound (Soda-lime) contained in a canister.
    • Advantages
    • -> Economy of fresh anaesthetic gases
    • -> Economy of volatile agents
    • -> Warms and humidifies inspired gases
    • -> Reduced contamination of atmosphere by waste anaesthetic gases.
    • Disadvantages
    • -> The system is expensive
    • -> Slow changes in concentration of inspired volatile agents in closed and low flow systems
    • -> Valves increase resistance to breathing
    • -> Soda Lime is irritant to tissues
    • -> Soda Lime canister contributes to mechanical dead space
    • ->Nitrous Oxide may only be used when fraction of inspired oxygen in a gas mixture (FIO2) can be monitored
  29. Soda Lime

    Slide 29 - Soda Lime

    • Soda Lime is a mixture of 94% Calcium Hydroxide, 5% Sodium Hydroxide and 1% Potassium Hydroxide
    • NaOH and KOH are added to accelerate the rate of absorption.
    • Fresh soda lime contains 35% water as the CO2 must be dissolved before it can react
    • Soda lime contains a pH sensitive dye which indicates exhaustion
    • QMH Soda Lime changes from green to purple
    • The canister should be changed when 50% of the soda lime has changed colour
    • The colour change can return to their original colour if left to stand alone for long enough, therefore the canister should be changed prior to anaesthesia if there is any doubt of its freshness.
  30. Circle System

    Slide 30 - Circle System

    • Consists of:
    • C: Soda lime canister
    • B: Breathing bag
    • Vi: Inspiratory Valve
    • Ve: Expiratory Valve
    • (both are unidirectional)
    • F: Fresh gas supply
    • V: APL valve
    • The system is connected to the patient via hosing and a Y Piece which are attached to the unidirectional valves.
    • The circle system is suitable for patients weighing more than 10kg
  31. Function

    Slide 31 - Function

    • Inspiration:
    • -> The expiratory valve closes, and gas flows from the breathing bag to the patient via the inspiratory limb of the circuit.
    • Expiration:
    • -> The inspiratory valve closes, gas flows into the breathing bag via the expiratory limb. Carbon Dioxide is absorbed by the soda lime canister. Excess gas leaves via the APL valve.
  32. Closed and Semi closed

    Slide 32 - Closed and Semi closed

    • The circle system may be used as a closed or semi-closed system
    • Closed systems:
    • The APL valve is closed. Oxygen flows into the system to replace what's consumed by the patient. Expired CO2 is absorbed by soda lime.
    • Advantages:
    • Volatile agent and Oxygen consumption is minimised, as well as atmospheric pollution.
    • Disadvantages:
    • The system is unstable – if the fresh gas flow is not matched exactly to the patient oxygen consumption, the system will over fill
    • Semi-closed systems:
    • The APL valve is opened, allowing gas to escape from the system, this allows higher fresh gas flow rates to be used
    • Initially use a high flow rate and vaporiser setting to raise the concentration of anaesthetic in the circuit, they can then be reduced for maintenance
    • Advantages:
    • The system is more stable – excess gas will be lost via the APL valve
    • Disadvantages:
    • Increased volatile agent and oxygen consumption, as well as atmospheric pollution
  33. Unidirectional valves

    Slide 33 - Unidirectional valves

    • Of turret type – The pressure generated by the patients breathing caused the disc to rise and allow gas to pass in one direction only.
    • Discs can be made of misc, ceramic or plastic
    • Plastic is the less expensive but can warp and stop them working correctly. They can stick.
    • Inefficient valves will reduce the efficiency of gas circulation and result in rebreathing and CO2 retention
  34. Vaporisers in circle systems

    Slide 34 - Vaporisers in circle systems

    • Vaporisers can be positioned either in or out of the circuit
    • Vaporiser in circuit (VIC)
    • -> A low resistance vaporiser placed in the inspiratory limb of the circle.
    • -> Anaesthetic agent is vaporised by the gases circulated around the system by the patients breathing
    • For example if the patient becomes too light, respiration becomes less depressed, minute volume will increase, more agent will be vaporised thus increasing concentration of volatile agent.
    • -> Designed to offer minimal
    • resistance to gas flow
  35. Vaporisers out of circuit (VOC)

    Slide 35 - Vaporisers out of circuit (VOC)

    • -> Positioned on the back bar of the anaesthetic machine
    • -> They are high efficiency vaporisers that can deliver high output concentrations at low flows
    • -> The rate of change of anaesthetic concentration in the circuit depends upon the fresh gas flow rate
    • -> Resistance is greater than that of the VIC
  36. Advantages

    Slide 36 - Advantages

    • Economy of anaesthetic consumption
    • Warming and humidification of inspired gases
    • Reduced atmospheric pollution
    • Suitable for IPPV and can be attached to a ventilator
    • More efficient absorption of CO2 by soda lime
    • Disadvantages
    • Unstable if used closed
    • Slow changes of the anaesthetic concentration with low flows and VOC
    • Complex construction prone to malfunction?
    • Bulky
    • Expensive
  37. To-and-fro (waters canister)

    Slide 37 - To-and-fro (waters canister)

    • Consists of:
    • C: CO2 canister
    • B: Breathing bag
    • F: Fresh gas supply
    • P:Patient connection
    • V: APL valve
    • Not generally used in small animal practice, used more in large animals
  38. Function

    Slide 38 - Function

    • Much like the circle system, but the patient breathes to and fro into the circuit
  39. Advantages

    Slide 39 - Advantages

    • Inexpensive
    • Portable
    • Disadvantages
    • Canister is positioned close to the patients head – patient more likely to breathe in soda lime dust – irritant
    • Soda lime becomes exhausted quicker due to breathing pattern
    • The canister is horizontal – unless tightly packed, the soda lime settles and the gas channels over the soda lime causing rebreathing
  40. Humphrey ADE

    Slide 40 - Humphrey ADE

    • Developed by Dr Humphrey 1981
    • Single circuit that can be used on patients weighing up to 100kg
    • Can be changed from a Mapleson A system to a Mapleson D system
    • A removable Soda lime canister can be used to create a rebreathing system
    • Humphreys block (metal block) consists of:
    • -> APL Valve
    • -> Reservoir bag (on fresh gas inlet end of circuit)
    • -> Ventilator port
    • -> Lever
    • -> Over pressure valve
  41. functions

    Slide 41 - functions

    • With the lever up (spontaneous mode) the breathing bag and APL valve are connected creating a Mapleson A (magill system)
    • With the lever down (ventilator mode) the breathing bag and APL valve are disconnected, the ventilator port is opened creating a Mapleseon D (Bain) for controlled ventilation
    • If no ventilator is attached and the port is left open the system will function like a Mapleson E
    • When the Soda lime canister is attached, the system operates as a circle system – the lever can then be moved to allow for either spontaneous or controlled ventilation
  42. Advantages

    Slide 42 - Advantages

    • One system safe for patients under 100kg
    • Can switch between a rebreathing and non rebreathing system
    • Lower flow rates in both modes
    • Warmed humidified gases
    • Low resistance
    • Can be attached to a ventilator
    • MRI compatible
    • Disadvantages
    • Expensive
    • Bulky
  43. Fresh gas flow requirements

    Slide 43 - Fresh gas flow requirements

    • Mapleson Classification
    • Common name
    • Rebreathing / non-rebreathing
    • General classification
    • Fresh gas flow requirement
    • (for spontaneous ventilation)
    • A
    • Magill / Lack (parallel or co-axial)
    • Non rebreathing
    • Semi-closed
    • 1 x MV
    • D
    • Bain (co-axial)
    • Non
    • Semi-closed
    • 2.5-3 x MV
    • E
    • Ayres T-piece
    • Non
    • Semi-closed
    • 2.5-3 x MV
    • F
    • Jackson Rees modification
    • Non
    • Semi-closed
    • 2.5-3 x MV
    • To-and-fro
    • Rebreathing
    • Closed
    • 100ml/kg/min initially then 10ml/kg/min
    • Circle
    • Rebreathing
    • Closed
    • 100ml/kg/min initially then 10ml/kg/min