INHALATION ANAESTHESIA BREATHING SYSTEMS Prepare and monitor anaesthesia in animals INHALATION ANAESTHESIA BREATHING SYSTEMS

Inhalation Anesthesia Can be used for both induction & maintenance Delivers O 2 Removes CO 2 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 warmedGas warmed by patient Gas humidified by patient $

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 O2O2 O 2 + V Soda Lime 10mL/kg/min O 2 metabolised Anaesthetic vapour absorbed CO 2 removed

INHALATION ANAESTHESIA BREATHING SYSTEMS Vaporiser inside circle V O2O2 V Soda Lime 10mL/kg/min O 2 metabolised Anaesthetic vapour absorbed CO 2 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 Ayres (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 patient expired Fresh Gas

INHALATION ANAESTHESIA BREATHING SYSTEMS Ayres (T-Piece) Configuration O2-in tube is completely separate from exhaust tube

INHALATION ANAESTHESIA BREATHING SYSTEMS Bains (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 CO 2

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 Circle Expiratory One-way valve Inspiratory One-way valve Soda Lime Canister Rebreathing 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 valves

INHALATION ANAESTHESIA BREATHING SYSTEMS One-way valves

INHALATION ANAESTHESIA BREATHING SYSTEMS One-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 BainKing

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

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 CO 2 Calcium Carbonate CO 2 CaCO 3 calcium carbonate lime (gardening) calcite chalk (older types) seashell antacid

INHALATION ANAESTHESIA BREATHING SYSTEMS Soda Lime Exhaustion & Confusion White PurplePink White OR 2 colour changes possible –According to brand of soda lime Loses colour change if not replaced 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 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 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/min Ball-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 O 2 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 O 2 supply doesnt 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 O 2 Pressures PsiAtmCm H2O kPa Bottle out Regulator out Circuit atm = approx 100kPa

INHALATION ANAESTHESIA BREATHING SYSTEMS Which system to use? < 7-10 kg> 7-10 kg Non-Rebreathing Ayres T-piece Bain (?) Rebreathing Circle To and Fro Non-Rebreathing Bain 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 O mL/kg/min N 2 O 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

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