anaesthesia Breathing circuits and its classification and functional analysis
- 1. Breathing circuits By:- DR. PRATEEK GUPTA PG ANESTHESIA (1ST YEAR)
- 2. WHAT IS IT • Assembly of components which connects the patient’s airway to the anaesthetic machine creating an artificial atmosphere, from and into which the patient breathes. • A breathing system converts continuous flow from the machine to a intermittent flow.
- 3. INTRODUCTION • Any resemblance to a breathing system was developed by Barth (1907) • The Mapleson A (Magill) system was designed by Sir Ivan Magill in the 1930's
- 4. • In 1936, Brian Sword introduced the circle system • Ayre’s T-piece was introduced in 1937 • Bain Circuit was introduced in 1972 by Bain and Spoerel.
- 5. • Fresh gas entry port, through which gases are delivered from machine to system • Port to connect it to the patient • Reservoir for gas, to meet peak inspiratory flow requirements • Expiratory port through which expired gas is vented to to atmosphere • A CO2 absorber • Corrugated tubes for connecting these components
- 6. COMPONENTS 1.Bushings (mount) 2.Sleeves 3.Connectors & Adaptors 4.FGF inlet 5.Breathing tube 6.Reservoir Bag 7.Valve’s 8.Filters 9.CO2 absorber
- 7. Criteria ideal system • ESSENTIAL 1.Delivery of gas from machine to the alveoli in same concentration as set and in shortest possible time 2.Effective elimination of CO2 3.Minimal dead space 4.Minimal resistance
- 8. DESIRABLE 1.Economy of fresh gas 2.Conservation of heat 3. Adequate humidification 4.Efficient during spontaneous and controlled ventilation
- 9. CONTD.. 5. Efficient for adult, pediatrics and with mechanical ventilators 6. Light weight 7. Less theater pollution 8. Convenient during use.
- 10. CLASSIFICATION • McMOHAN in 1951 • OPEN - no rebreathing • SEMICLOSED - partial rebreathing • CLOSED - total rebreathing
- 11. Dripps, eckenhoff and vandam • Based on presence or absence of -Reservoir bag -Rebreathing -CO2 absorption -Directional valve • Insufflation- gases are delivered directly into patient’s ariway
- 12. TYPE INHALATION EXHALATI ON RESERVOIR REBREATHI NG CO2 ABSORPTN EXAMPLE OPEN AIR + AGENT Atmospher e - - - Open drop T-Piece SEMI-OPEN AIR + AGENT FROM MACHINE Atmospher e SMALL MINIMAL (on FGF) - T-Piece with small reservoir SEMI- CLOSED From Machine Atmospher e+ Machine large possible + Magill attachment Mapleson systems CLOSED From Machine Atmospher e+machine Large Possible + Circle system
- 13. CONWAY • Breathing systems with CO2 absorber • Breathing systems without CO2 absorber.
- 14. BREATHING SYSTEMS WITHOUT CO2 ABSORPTION BREATHING SYSTEMS WITH CO2 ABSORPTION Unidirectional flow A) Non rebreathing systems. B) Circle systems. Unidirectional flow Circle system with absorber.
- 15. BREATHING SYSTEMS WITHOUT CO2 ABSORPTION BREATHING SYSTEMS WITH CO2 ABSORPTION Bi-directional flow A) Afferent reservoir systems. - Mapleson A,B,C - Lack’s system. B) Enclosed afferent reservoir systems Miller’s (1988) Bi-directional flow To and Fro system.
- 16. BREATHING SYSTEMS WITHOUT CO2 ABSORPTION c) Efferent reservoir systems Mapleson D Mapleson E Mapleson F Bain’s system d) Combined systems Humphrey ADE Multi circuit system
- 17. NONREBREATHING SYSTEM (Uni-directional) • Uses non-rebreathing valve • No mixing of fresh gas and expired gas • Fresh gas flow =/> Minute volume
- 19. DISADVANTAGE • FGF has to be constantly adjusted so uneconomical • No humidification • No conservation of heat • Not convenient because of bulk of valve • Valve malfunctioning due to condensation of moisture
- 20. Bi directional flow • Extensively used • Depend on the FGF for effective elimination of CO2 • FGF - No FGF - suffocated - Low FGF - does not eliminate CO2 - - High FGF - wastage • FGF should be delivered as near the patient’s airway as possible.
- 21. MAPLESON SYSTEM • 1954 by Professor W W Mapleson - Maplesons A- (Magills) - Maplesons B - Maplesons C - Maplesons D - Maplesons E (T-piece) - Maplesons F (Jackson-Rees modification of the T-piece)
- 23. FUNCTIONAL CLASSIFICATION • Afferent reservoir system (ARS). • Enclosed afferent reservoir systems (EARS). • Efferent reservoir systems (ERS). • Combined systems. • Enclosed afferent reservoir system has been described by Miller and Miller.
- 24. • AFFERENT LIMB - delivers the fresh gas from the machine to the patient. • EFFERENT LIMB - expired gas from the patient and vents it to the atmosphere through the expiratory valve/port
- 25. AR SYSTEMS • SPONTANEOUS BREATHING - the expiratory valve is separated from the reservoir bag - FGF should be atleast one MV - Apparatus dead space is minimal. • CONTROLLED VENTILATION -Not efficient • FGF close to the expiratory valve (Mapleson B & C) , the system is inefficient both during spontaneous and controlled ventilation
- 26. MAPLESON A (Magill’s) • PIC
- 27. MAPLESON A • Also known as “MAGILLS SYSTEM” • Best for spontaneous ventilation • Depend on FGF for CO2 washout so also known as “FLOW CONTROLLED BREATHING SYSTEM” • No rebreathing if FGF=minute volume • No separation of inspired and expired gases • Monitoring of ETCO2 is must.
- 28. • APL valve at patient end. • FGF and RB at other end of system • Only one tubing so mixing of gases • Work of breathing is less • Length of corrugated tube 110cm / volume=550ml
- 30. • FGF requirements -SPONTANEOUS • FGF = Minute volume FGF of 51-85ml/kg/min advised to prevent re-breathing or 42-88% of MV -CONTROLLED • FGF = 2.5 x MV
- 31. MAPLESON A Inspiration • The valve closes • Patient inspires FG from the reservoir bar • FG flushes the dead space gas towards patient
- 32. Expiration • The pt expires into the reservoir bag • The initial part of the expired gas is the dead space followed by alveolar gas • Meets up with FG, pressure in the circuit increases forces the APL open
- 34. CONTROLLED VENTILATION • INEFFCIENT. • Venting of gas occurs during the inspiratory phase, and the alveolar gases are retained in the tubing during expiration phase
- 35. • Hence the alveolar gas is rebreathed before the pressure in the system increases sufficiently enough to force the expiratory valve open • A Fresh gas flow of >20l/min is required to prevent rebreathing
- 36. • This system differs from other circuits in that the fresh gas does not enter the system near the patient but near the reservoir bag. • HAZARD- should not be used with mechanical ventilator coz entire system becomes dead space
- 37. • Test for Mapelson “A” • Occlude patient end, close APL valve, pressurize system – maintaining pressure confirms integritiy
- 38. LACK’S MODIFICATION • In 1976; Lack modified the mapelson A. - APL valve at other end - Added expiratory limb so no mixing of gas. Two arrangement; -Dual arrangement (parellel) -Tube within tube (co-axial)
- 41. • Tube length 1.5 m • Outer tube diameter – 30 mm • Inner tube diameter - 14 mm • Inspiratory capacity - 500 ml
- 42. TESTING • 1)Attach tracheal tube to inner tube at patient end ; blowing down the tube with APL valve closed will produce bag movement if there is leak between two tubes • 2) Occlude both limbs at patient end with APL valve open; squeeze the bag; if there is leak in inner tube; gas will escape from APL valve and bag will collapse
- 43. • Advantages:- • Location of APL valve- facilitates IPPV / scavenging. • Disadvantages:- • Slight increase in work of breathing. • Break / disconnection of inner tube- entire reservoir tube becomes dead pace.
- 44. Mapleson B • Fresh gas inlet near pt and distal to APL • APL opens when pressure in the circuit rises and an admixture of alveolar gas and FG is discharged • During Inspiration, a mixture of alveolar gas and FG is inhaled • Avoid rebreathing with FGF>2×MV, not very efficient
- 46. Mapleson C • Also known as Water to and fro (Water’s Circuit) • Similar in construction to the Mapleson B but main tubing shorter • As efficient as Mapleson A if expiratory pause is minimal • FGF is equal to 2×MV to prevent rebreathing • CO2 builds up slowly with this circuit, not efficient
- 48. ENCLOSED AFFERENT RESERVOIR SYSTEMS (EARS)
- 49. • UTILIZATION ??? 82?/93?74?
- 50. EFFERENT RESERVOIR (ER) SYSTEMs • Mapleson’s D, E ,F and bain circuits • 6 mm tube as the afferent limb that supplies the FG from the machine • ER systems are modifications of Ayre’s T-piece • Work efficiently and economically for controlled ventilation
- 51. MAPELSON D • Incorporates T piece at patient • RB and APL valve at other end • FGF enters the system through side arm of T piece • FGF required to prevent rebreathing is 1.5-2 times minute volume • Used for spontaneous and controlled ventilation
- 52. BAIN’S SYSTEM • Described by Bain & Spoerel in 1972 • Modification of Mapelson D system • Added one more tube; arranged coaxially • Inner tube inspiratory; outer tube expiratory+inspiratory • Length of tube: 1.8m • Outer tube diameter: 22mm • Inner tube diameter :7mm
- 58. FACTORS THAT TEND TO DEC REBREATHING (SPONT) • HIGH I:E RATIO • SLOW RISE IN INSPIRATORY FLOW RATE • A LOW FLOW RATE IN LAST PART OF EXPIRATION • A LONG EXPIRATORY PAUSE (BEST)
- 60. • Fresh Gas Flow required: • SPONTANEOUS: 150–200 ml/kg/min • CONTROLLED : • 70 ml/kg/min adult >60kgs • 3.5 L/min for 10 – 50 kgs • 2L/min for infants < 10kgs
- 61. advantage • Useful for pediatric as will as adult patient • Allows warming & humidification of gases • useful for spontaneous as will as controlled ventilation • Easily dismantled; sterilised; so useful in infected cases •
- 62. Contd. • Facilitates scavenging • Length of tubing is long so machine can be taken away from patient ; useful in head & neck & Neurosurgery. • Light weight • Can be used with ventilator
- 63. Disadvantage • High fresh gas flow requirements • Cannot be used with intermittent flow machine. • Disconnection, kink, break, leak, at inner tube may go unnoticed – entire exhalation limb becomes dead space
- 64. Functional analysis • During controlled ventilation -when FGF is high, PaCO2 becomes ventilatory dependent. • -when MV exceeds FGF, PaCO2 becomes dependent on FGF
- 65. testing • A) Foex-Crempton Smith test • Set low flow of O2 on flow meter , close APL valve • Occlude the inner tube with a finger or barrel of syringe at pt end . • Observe flow meter indicator • If inner tube is intact and correctly connected flow meter will fall • B) Pethik test • Close APL valve, Activate O2 flush • Observe the bag • Due to venturi effect , Bag will deflate .
- 66. Testing for outer tube • Close APL valve, occlude the patient end & pressurize the system. If no leak pressure will be maintained. When APL valve is opened the bag will deflate easily.
- 67. Ayre's T-piece Designed as a no valve circuit for paediatrics in 1937 by Philip Ayre. (Later classified as Mapleson E). • pic
- 69. T piece system • The Mapleson E (T-Piece), has a length of tubing attached to the T-piece to form a reservoir • Uses have decreased because of difficulties in scavenging • Still commonly used to administer oxygen or humidified gas to intubated patients breathing spontaneously • There are numerous modifications
- 70. Mapleson e • For spontaneous ventilation,the expiratory limb is left open • For controlled ventilation,the expiratory linmb is intermittently occulded and fresh gas flow inflate the lungs (risk of barotrauma) • Rebreathing will depend on the FGF,the volume of the expiratory limb,the patient’s minute vent. And the type of ventilation,i.e. spont versus controlled
- 72. Mapleson F(Jackson-Rees System) • This is a modification of the T-piece with a bag that has a venting mechanism- usually a hole • Adjustable pop-off valve can even be included to prevent over pressuring • Scavenging can be done
- 75. Mapleson F (Jackson Rees) • For spontaneous ventilation the relief mechanism is usually left open • For assisted of controlled ventilation, the relief mechanism is occluded sufficient enough to distend the bag, respiration can then be controlled by squeezing the bag
- 76. • The volume of the reservoir bag should be approximately the patient’s tidal volume, if the volume is too large re-breathing may occur and if too small ambient air may be entrained • To prevent rebreathing the system requires an FGF of 2.5-3 × the patients Minute volume
- 77. • FGF requirements:- • Spontaneous- 2-3 times MV • Minimum flow 3L/min • Controlled- 1000ml + 100ml/kg
- 78. ADVANTAGES • Compact • Cheap • No valves • Minimal dead space • Minimal resistance to breathing/less work of breathing • Ventilator can be used
- 79. disadvantages • The bag may become twisted and impede breathing • High gas flow requirements
- 80. Relative Efficiency of rebreathing among various Mapleson circuits • Spontaneous Ventilation-A>DFE>CB • Controlled Ventilation-DFE>BC>A • Mapleson A is most efficient during spontaneous ventilation, but it is the worst for controlled ventilation • Mapleson D is most efficient during controlled ventilation
- 85. ADVANTAGES OF MAPLESON • Simple, inexpensive & rugged • Variation in MV effect ETCO2 less than circle • In Coaxial, Inspiratory limb heated by warm exhaled gas • Can be used to ventilate patient in MRI unit • Lightweight, no drag on mask or tracheal tube
- 86. DISADVANTAGES OF MAPLESON • Requires high FGF • Inspired heat and humidity is low (unless device is used) • In A, B, and C APL valve near patient, hence inaccessible to the operator. Scavenging is awkward • Not suitable for malignant hyperthermia, not possible to increase FGF enough to remove increased CO2 load
- 87. insufflation • The blowing of anesthetic gases across a patient’s face • Avoids direct connection between a breathing circuit and a patient’s airway • Because children resist the placement of a face mask or an IV line, insufflation is valuable • CO2 accumulation is avoided with insufflation of oxygen & air at high flow rate (>10 L/m) under H & N draping at ophthalmic surgery • Maintain arterial oxygenation during brief periods of apnea
- 89. Draw-over anesthesia • Non-rebreathing circuits • Use ambient air as the carrier gas • Inspired vapor and oxygen concentrations are predictable & controllable • Advantage; simplicity, portability • Disadvantage; absence of reservoir bag -> not well appreciating the depth of TV during spontaneous ventilation
- 91. Disadvantages of the insufflation & draw-over systems • Poor control of inspired gas concentration & depth of anesthesia • Inability to assist or control ventilation • No conservation of exhaled heat or • humidity • Difficult airway management during • head & neck surgery • Pollution of the operating room with large volumes of waste gas
- 92. COMBINED SYSTEM HUMPHREY’S ADE system: • To overcome the difficulties of changing breathing system for different modes of ventilation this system is developed • Two reservoir bag; one in afferent limb; other in efferent limb; only one is in use at a time • System can be changed from ARS to ERS by changing the position of lever • Used for adults as will as children • Functional Analysis same as MAP-A in ARS& as BAIN in ERS
- 93. Humphrey’s pic
- 94. Circle system • ESSENTIAL CPMPONENT: • Soda lime canister • Two unidirectional valve • FGF entry • Y piece • Reservoir bag • Relief valve
- 95. CRITERIA FOR EFFICIENT FUNCTIONING • Two unidirectional valve on either side of RB • Relief valve on expiratory limb • FGF should enter proximal to inspiratory unidirectional valve
- 98. TESTING • Set all the gas flows to zero. • Close APL valve • Occlude Y piece • Pressurize system to 30cm of with Oxygen flush • Pressure should remain fixed for at least 10 sec. • Open APL valve and ensure pressure decrease
- 99. ADVANTAGES • Exhaled gas–CO2 used again and again • Constant inspired concentration • Conservation of heat & humidity • Useful for all ages • Useful for low flow ;reduces cost of Anaesthesia • Low resistance • Less OT pollution •
- 100. DISADVANTAGES • Increased dead space • Malfunctioning of unidirectional valve • Exhausted soda lime; danger of hypercarbia