anaesthesia Breathing circuits and its classification and functional analysis

anaesthesia breathing circuits. mapleson circuits. classification of circuits. functional analysia of circuits. draw over circuit. advantages and disadvantages of different circuits.

1. Breathing circuits By:- DR. PRATEEK GUPTA PG ANESTHESIA (1 ST 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 CO 2 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.CO 2 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 -CO 2 absorption -Directional valve Insufflation- gases are delivered directly into patient’s ariway

12. TYPE INHALATION EXHALATION RESERVOIR REBREATHING CO 2 ABSORPTN EXAMPLE OPEN AIR + AGENT Atmosphere - - - Open drop T-Piece SEMI -OPEN AIR + AGENT FROM MACHINE Atmosphere SMALL MINIMAL (on FGF) - T-Piece with small reservoir SEMI-CLOSED From Machine Atmosphere+ Machine large possible + Magill attachment Mapleson systems CLOSED From Machine Atmosphere+machine Large Possible + Circle system

13. CONWAY Breathing systems with CO 2 absorber Breathing systems without CO 2 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

18. 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

19. Bi directional flow E xtensively used D epend 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.

20. 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)

21. 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.

22. 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

23. 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

24. MAPLESON A (Magill’s) PIC

25. MAPLESON A Also known as “MAGILLS SYSTEM” Best for spontaneous ventilation Depend on FGF for CO 2 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.

26. 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

27. 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

28. MAPLESON A  Inspiration The valve closes Patient inspires FG from the reservoir bar FG flushes the dead space gas towards patient

29. 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

30. CONTROLLED VENTILATION INEFFCIENT . Venting of gas occurs during the inspiratory phase, and the alveolar gases are retained in the tubing during expiration phase

31. 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

32. 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

33. Test for Mapelson “A” Occlude patient end, close APL valve, pressurize system – maintaining pressure confirms integritiy

34. 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)

35. Tube length 1.5 m Outer tube diameter – 30 mm Inner tube diameter - 14 mm Inspiratory capacity - 500 ml

36. 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

37. 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.

38. 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

39. 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 M apleson A if expiratory pause is minimal FGF is equal to 2×MV to prevent rebreathing CO 2 builds up slowly with this circuit , not efficient

40. ENCLOSED AFFERENT RESERVOIR SYSTEMS (EARS)

41. UTILIZATION ??? 82?/93?74?

42. 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 W ork efficiently and economically for controlled ventilation

43. 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

44. 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

45. 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)

46. Functional analysis pic

47. 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

48. 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

49. 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

50. 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

51. Functional analysis During controlled ventilation - when FGF is high, PaCO2 becomes ventilatory dependent. - when MV exceeds FGF, PaCO2 becomes dependent on FGF

52. 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 .

53. 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.

54. Ayre's T-piece Designed as a no valve circuit for paediatrics in 1937 by Philip Ayre . (Later classified as Mapleson E). pic

55. 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

56. 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

57. 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

58. 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

59. 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

60. FGF requirements:- Spontaneous- 2-3 times MV Minimum flow 3L/min Controlled- 1000ml + 100ml/kg

61. ADVANTAGES Compact Cheap No valves Minimal dead space Minimal resistance to breathing/less work of breathing Ventilator can be used

62. disadvantages The bag may become twisted and impede breathing High gas flow requirements

63. 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

64. ADVANTAGES OF MAPLESON Simple, inexpensive & r ugged Variation in MV effect ETCO 2 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

65. 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 CO 2 load

66. 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

67. 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

68. 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

69. 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

70. Humphrey’s pic

71. Circle system ESSENTIAL CPMPONENT: Soda lime canister Two unidirectional valve FGF entry Y piece Reservoir bag Relief valve

72. 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

73. 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

74. ADVANTAGES Exhaled gas–CO 2 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  

75. DISADVANTAGES Increased dead space Malfunctioning of unidirectional valve Exhausted soda lime; danger of hypercarbia