inhalation anaesthesia breathing systems prepare and monitor anaesthesia in animals inhalation...

INHALATION ANAESTHESIA BREATHING SYSTEMS

Prepare and monitor anaesthesia in animals

INHALATION ANAESTHESIA

BREATHING SYSTEMS

INHALATION ANAESTHESIA BREATHING SYSTEMS

INHALATION ANAESTHESIA BREATHING SYSTEMS

Inhalation Anesthesia

• Can be used for both induction & maintenance

• Delivers O2

• Removes CO2

• Vaporizes volatile anesthetic liquids– Controls amount of anesthetic delivered

• Can assist ventilation

INHALATION ANAESTHESIA BREATHING SYSTEMS

2 Basic Systems

• Rebreathing

• Non-Rebreathing

INHALATION ANAESTHESIA BREATHING SYSTEMS

Flow of oxygen

• Re-breathing– To & Fro flow (horses)– Circular flow (humans, pets>7-10kg)

• Vaporiser within the circle• Vaporiser outside the circle

• Non-rebreathing– One-way flow (pets<10kg)

• T-piece• Baines• Magill

INHALATION ANAESTHESIA BREATHING SYSTEMS

Advantages of Rebreathing

• Less waste of oxygen

• Less waste of anaesthetic

• Gas warmedwarmed by patient

• Gas humidified by patient

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INHALATION ANAESTHESIA BREATHING SYSTEMS

Advantages of Non-Rebreathing

• Less dead space– Smaller tubes

• Less pressure required (low resistance)– No valves to move– No need for animal to force gas through

the circle

INHALATION ANAESTHESIA BREATHING SYSTEMS

Principles of Design

• Resistance to moving air– Tubing surface friction– Valve movement friction– Head on gas flows– Gas flow around corners– Soda lime crystals

• Dead space– Machine & tubing dead space– Physiological (airway) dead space

• Pressure relief valve (=pop-off valve)• Rebreathing bag (=reservoir bag)

INHALATION ANAESTHESIA BREATHING SYSTEMS

Why T-piece needs high O2 flow…

• O2 is used to flush the tubing of expired gas– Avoids rebreathing CO2

INHALATION ANAESTHESIA BREATHING SYSTEMS

2 Vaporiser Locations

• Re-breathing Vaporiser – Vaporiser in circle

• Stephens Machine

• Non-rebreathing Vaporiser outside any system– Vaporiser ‘outside’ any system

• ‘Tec’ Series

INHALATION ANAESTHESIA BREATHING SYSTEMS

Vaporiser outside circle

V

O2 O2+ V

Soda LimeSoda Lime

10mL/kg/min O2 metabolised

Anaesthetic vapour absorbed

CO2 removed

INHALATION ANAESTHESIA BREATHING SYSTEMS

Vaporiser inside circle

V

O2

V

Soda LimeSoda Lime

10mL/kg/min O2 metabolised

Anaesthetic vapour absorbed

CO2 removed

INHALATION ANAESTHESIA BREATHING SYSTEMS

VOC

INHALATION ANAESTHESIA BREATHING SYSTEMS

VIC

INHALATION ANAESTHESIA BREATHING SYSTEMS

Non-Rebreathing Configurations

→Bain(1)

Magill

→ Lack

Jackson-ReesAyre

→ Bain(2)→ Modified to…

→ Bain(3)

INHALATION ANAESTHESIA BREATHING SYSTEMS

Magill Configuration

• Used in animals > 7-10kg – Due to expiratory valve resistance– Use 200 mL/kg/minute

• Forced ventilation can be difficult

INHALATION ANAESTHESIA BREATHING SYSTEMS

Lack Configurations

• Tube-in-tube variation (of Magill)

• Parallel tube variation (of Magill)

INHALATION ANAESTHESIA BREATHING SYSTEMS

Ayre’s (T-Piece) Configuration

• Low resistance (no valves)– So ideal for animals < 10 kg

INHALATION ANAESTHESIA BREATHING SYSTEMS

The T-Piece

• Simply describes the shape of the junction

patientexpired

Fresh Gas

INHALATION ANAESTHESIA BREATHING SYSTEMS

Ayre’s (T-Piece) Configuration

• O2-in tube is completely separate from exhaust tube

INHALATION ANAESTHESIA BREATHING SYSTEMS

Bain’s (tube-in-tube) Configuration

• Bain modification of Mapleson D or E non-rebreathing configuration– O2-in tube hidden inside exhaust tube– Ok for forced (positive pressure) ventilation– With or without valves/bag

INHALATION ANAESTHESIA BREATHING SYSTEMS

Bain Variations

Without Valves (<10kg)

Parallel Bain

Bain with bag

Bain connected directly to O2 outlet

With Valves (>10kg)Bain (1)

Bain (2)

Bain (3)

INHALATION ANAESTHESIA BREATHING SYSTEMS

Damaged Bain

• Undetected internal leaks cause high CO2

INHALATION ANAESTHESIA BREATHING SYSTEMS

Bag or No bag?

• Breathing Bag permits positive pressure ventilation (emergencies etc)

INHALATION ANAESTHESIA BREATHING SYSTEMS

Stephens Circle

• Increased or Forced breathing → increased vaporizer output

INHALATION ANAESTHESIA BREATHING SYSTEMS

CircleExpiratory One-way valve

Inspiratory One-way valve

Soda Lime Canister

Rebreathing bagRebreathing bag

Pop-off valve

Waste Anaesthetic Gases(WAG) scavenge tube

INHALATION ANAESTHESIA BREATHING SYSTEMS

One-way Valves

• Attached to inspiratory & expiratory tubes

• Many mechanical types– Vary with degree of force required to move

them• Light plastic flaps

– For smaller patients want low force requirement

• Heavy plates– For heavy duty use on larger patients

INHALATION ANAESTHESIA BREATHING SYSTEMS

One-way valvesOne-way valves

INHALATION ANAESTHESIA BREATHING SYSTEMS

One-way valvesOne-way valves

INHALATION ANAESTHESIA BREATHING SYSTEMS

One-way valvesOne-way valves

INHALATION ANAESTHESIA BREATHING SYSTEMS

Circle Tube-in-Tube(Universal F-Circuit,King modification)

Parallel Tubes•Large (>10kg)•Paediatric (7-10kg)

Rebreathing Hoses

Y-Piece

‘F-Piece’

INHALATION ANAESTHESIA BREATHING SYSTEMS

Note: 2 kinds of tube-in-tube (Coaxial)

• Rebreathing– ‘King’ modification of circle

• Non-Rebreathing – ‘Bain’ modification of T-piece

Bain King

INHALATION ANAESTHESIA BREATHING SYSTEMS

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INHALATION ANAESTHESIA BREATHING SYSTEMS

To and Fro

• Carbon dioxide absorber is very close to endotracheal tube attachment

• Lower resistance• Can result in

superheated air being breathed in as it passes over soda lime- there have been cases reported where respiratory tract damage has resulted

INHALATION ANAESTHESIA BREATHING SYSTEMS

Soda Lime

INHALATION ANAESTHESIA BREATHING SYSTEMS

INHALATION ANAESTHESIA BREATHING SYSTEMS

Soda Lime

• 94% calcium hydroxide

• 5% sodium hydroxide

• 1% potassium hydroxide

INHALATION ANAESTHESIA BREATHING SYSTEMS

Soda Lime Chemistry

CO2 + H2O   H2CO3   H+ + HCO3-

NaOH + H2CO3   NaHCO3 + H2O

2NaHCO3 + Ca(OH)2   2NaOH + H2O + CaCO3

INHALATION ANAESTHESIA BREATHING SYSTEMS

CO2 Calcium Carbonate

CO2 CaCO3

•calcium carbonate•lime (gardening)•calcite•chalk (older types)•seashell•antacid

INHALATION ANAESTHESIA BREATHING SYSTEMS

Soda Lime Exhaustion & Confusion

White → Purple Pink → White

OR

• 2 colour changes possible– According to brand of soda lime

• Loses colour change if not replacedheat heat

INHALATION ANAESTHESIA BREATHING SYSTEMS

Soda Lime Canisters

• Transparent, or

• Opaque Stephens Machine

INHALATION ANAESTHESIA BREATHING SYSTEMS

Soda lime exhausted if

• Colour change (as indicated)

• Does not generate heat when in use

• Loses crumbly texture

INHALATION ANAESTHESIA BREATHING SYSTEMS

Pop-Off Valve

• Also = ‘Pressure Relief Valve’

• Valve tension adjusted by a screw mechanism

Weak Spring

INHALATION ANAESTHESIA BREATHING SYSTEMS

Pop-Off Valve

Waste gases

INHALATION ANAESTHESIA BREATHING SYSTEMS

Pop-Off ValvePop-Off Valve

INHALATION ANAESTHESIA BREATHING SYSTEMS

Flush Valve

• Also known as– ‘Quick Flush’ valve– ‘Oxygen Flush’ valve– ‘By-Pass’ valve

• By-passes vaporiser (VOC type) & Flowmeter

• Only use to flush out tubing– If patient connected risks pressure burst into lungs

• Delivers a very high 50-70L/min (@50 psi)

– Never use with Bain configuration

INHALATION ANAESTHESIA BREATHING SYSTEMS

Flush Valve

INHALATION ANAESTHESIA BREATHING SYSTEMS

Flush Valve

INHALATION ANAESTHESIA BREATHING SYSTEMS

Pressure valve

• Some machines– Backup in case of regulator failure

INHALATION ANAESTHESIA BREATHING SYSTEMS

Flowmeter

INHALATION ANAESTHESIA BREATHING SYSTEMS

Flowmeter

• Bobbin or Ball

             Bobbin flowmeter,

reading 2 l/minBall-float flowmeter,

reading 2 l/min

Read at top Read at middle

INHALATION ANAESTHESIA BREATHING SYSTEMS

Rebreathing Bag

= Reservoir bag• Bag size ~ Animal size

– Adjust pop-off valve and O2 flow rate to keep ½-3/4 full– Approx size = tidal vol (10 mL/kg) x 6 (eg 20 kg dog = 1.2 L)

• Required when O2 supply doesn’t match an inspiration– Most important in a circle system– Not really required in non-rebreathing system

• Also used for – Monitoring tidal volume– Assisted ventilation

• Thoracic surgery• In emergency resuscitation

INHALATION ANAESTHESIA BREATHING SYSTEMS

Anaesthetic tubing

• May be rubber, plastic• Usually corrugated

– Prevents kinking– Collects moisture

• Transports gases• Often condensation from expired gases

– Clean and hang to drain each day

• Avoid kinking• Tube Size ~ Animal Size

INHALATION ANAESTHESIA BREATHING SYSTEMS

O2 Pressures

Psi Atm Cm H2O

kPa

Bottle out 2000 136 13790

Regulator out 50 3.4 340

Circuit 0.43 0.03 30 3

1 atm = approx 100kPa

INHALATION ANAESTHESIA BREATHING SYSTEMS

Which system to use?

< 7-10 kg > 7-10 kg

Non-RebreathingAyres T-piece

Bain (?)

RebreathingCircle

To and Fro

Non-RebreathingBain

Magill

Lack

INHALATION ANAESTHESIA BREATHING SYSTEMS

What about 7-10 kg animals?

• Some practices use a paediatric (ie small diameter) circle tubing system

INHALATION ANAESTHESIA BREATHING SYSTEMS

To-and-Fro Configuration

• Horse anaesthesia– For large animal practices where

occasional longer anaesthetics are required

– Cheap alternative to an anaesthetic machine

– Highly portable & suitable for field use

– Robust - no moving parts – Can store for long periods w/o

need for maintenance

INHALATION ANAESTHESIA BREATHING SYSTEMS

The End

INHALATION ANAESTHESIA BREATHING SYSTEMS

Summary

• What are the 2 basic kinds of ‘breathing system’?– Rebreathing

• Use soda lime to absorb CO2– Circle

» VIC (e.g. Stephens)» VOC (e.g. Tec Series)

– To-and-Fro

– Non-Rebreathing• Use high flow rates to flush out CO2

– T-Piece– Baines

INHALATION ANAESTHESIA BREATHING SYSTEMS

O2 Flows

• Rebreathing (e.g. Circle)

–10 mL/kg/min (range 5-30)• At induction - 20• Usual spay maintenance, most spays -10• Long surgery maintenance - 5

• Non-rebreathing (e.g. T-Piece)

–200 mL/kg/min

INHALATION ANAESTHESIA BREATHING SYSTEMS

N2O Flows

• Non-Rebreathing (T-Piece)– Make up 1/2 or 2/3 of total flow, eg

• O2 100 mL/kg/min

• N2O 100 mL/kg/min

• Rebreathing (Circle)

INHALATION ANAESTHESIA BREATHING SYSTEMS

Re-Breathing Bag

• Should be kept full enough to accommodate each breath– Because rate of gas inflow may not be as

fast as an animals inspiration• This most important for closed/semiclosed

circle systems

• Monitors respiration depth & rate• Allows for positive pressure

ventilation if required

INHALATION ANAESTHESIA BREATHING SYSTEMS

Non-rebreathing

• Advantages– Known inspired concentration – No soda lime to change – Small dead space – Low resistance

• Disadvantages– Expensive to use – Increased use of natural resources – Pollution – Loss of water vapor – Loss of heat

INHALATION ANAESTHESIA BREATHING SYSTEMS

Forced Breathing

• Also known as– Positive Pressure Ventilation (PPV)– Intermittent Positive Pressure Ventilation (IPPV)

• Different machine configurations tolerate forced breathing differently– Valve pressure tolerances may be affected

• Anaesthetic depth can increase rapidly if using VOC machine (Stephens)

• Can cause lung injury (pulmonary barotrauma) if too much pressure

INHALATION ANAESTHESIA BREATHING SYSTEMS

INHALATION ANAESTHESIA BREATHING SYSTEMS

Activity 1

• What is an example of a rebreathing system?

• What is an example of a non rebreathing system?

• What is the basic difference between rebreathing and non rebreathing systems?

• Why are low resistance systems used?

INHALATION ANAESTHESIA BREATHING SYSTEMS

Activity 2

• Give three examples of low resistance systems?

INHALATION ANAESTHESIA BREATHING SYSTEMS

Activity 2 answers

• Mask

• T piece

• Chamber

• To & Fro system

INHALATION ANAESTHESIA BREATHING SYSTEMS

Activity 3

• What are the two categories of vaporisers?

INHALATION ANAESTHESIA BREATHING SYSTEMS

Activity 3 Answers

• Simple– Stephens machine

• Precision– Tec Series vaporisers

INHALATION ANAESTHESIA BREATHING SYSTEMS

Activity 4

• What factors do Precision Vaporisers compensated for?

INHALATION ANAESTHESIA BREATHING SYSTEMS

Activity 4 Answers

• Ambient temperature

• Flow rates

• Back pressure from patient (circuit resistance)

INHALATION ANAESTHESIA BREATHING SYSTEMS

Activity 5

• How do T pieces work?

INHALATION ANAESTHESIA BREATHING SYSTEMS

Non-rebreathing (e.g. Bain-no-valve)

INHALATION ANAESTHESIA BREATHING SYSTEMS

Activity 6

• What do the following parts of an anaesthetic machine do?– Cylinder– Regulator– Flowmeter– Oxygen flush valve– Vaporizer– One way valves– Gas tubing– Soda lime canisters– Pop off valve, escape valve– Scavenger system– Endotracheal tube

INHALATION ANAESTHESIA BREATHING SYSTEMS

The Real End