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Anaesthesia breathing systems


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Anaesthesia breathing systems

  2. 2. A breathing system is defined as an assembly of components which connects the patient’s airway to the anaesthesia machine creating an artificial atmosphere, from and into which the patient breathes. Definition
  3. 3. Anesthesia Breathing Systems Basic Principles • All anesthesia breathing systems have 2 fundamental purposes  Delivery of O2/Anesthetic gases  Elimination of CO2 (either by washout with adequate fresh gas flow (FGF) or by soda lime absorption)
  4. 4. Essential/ Principle Criteria The breathing system must a) Deliver the gases from the machine to the alveoli in the same concentration as set and in the shortest possible time. b) Effectively eliminate carbon-dioxide. c) Have minimal apparatus dead space. d) Have low resistance.
  5. 5. Desirable/Secondary Criteria The desirable requirements are a) economy of fresh gas. b) conservation of heat. c) adequate humidification of inspired gas. d) light weight e) Convenience during use. f) Efficient during spontaneous as well as controlled ventilation (efficiency is determined in terms of CO2 elimination and fresh gas utilization) g) Adaptability for adults, children and h) mechanical ventilators i) Provision to reduce theatre polluton j) Other function gas sampling, pressure and volume monitoring.
  6. 6. Components of breathing system: It primarily consists of a) A fresh gas entry port/delivery tube through which gases are delivered from the machine to the systems. b) A port to connect it to the patients airway. c) A reservoir bag for a gas in the form of a bag or a tube to meet the peak inspiratory flow requirements d) Breathing tubes e) Adjustable pressure limiting (APL) valve/pop off valve f) Connectors and adaptors g) Filters h) Humidification systems i) Peep valves ( manual and electronic)
  7. 7. RESERVOIR BAGS Composition Rubber, synthetic latex, neoprene. Ellipsoidal in shape. Available in sizes 0.5L to 3L. A normal size adult bag holds a volume exceeding the patients inspiratory capacity.
  8. 8. RESERVOIR BAGS Functions : i. Reservoir ii. Provides PIF. iii. It provides a means whereby ventilation may be assisted or controlled. iv. It protects the patient from excessive pressure in the breathing system. v. It can serve through visual & tactile observation as a monitor of patients spontaneous respiration.
  9. 9. Breathing Tubes 1. Made of rubber or plastic or silicone. 2. It may be coaxial or side by side. 3. Can be impregnated with silver to add antimicrobial effect. 4. Length is variable. 5. Internal diameter  Adults – 22mm.  Pediatric – 15mm. 6. Internal volume  400-500ml/metre. 7. Distensibility  0-5ml/metre/mmHg
  10. 10. Breathing Tubes 7. Resistance to gas flow  <1mm of H₂O/liter/min of flow 8. Corrugations prevent kinking & increased flexibility. Functions 1. Act as reservoir in certain systems. 2. They provide connection from 1 part of system to another.
  11. 11. Breathing Tubes  Backlash  seen during spontaneous breathing. Breathing tubes tend to collapse during inspiration and bulge during expiration. This may cause rebreathing.  Wasted ventilation  seen during controlled breathing. The tubes tend to bulge on positive pressure breath (inspiration) and return to resting position on exhalation. This results in less volume entering the patient than the one leaving the reservoir bag or a ventilator
  12. 12. Adjustable Pressure Limiting Valve (APL Valve) Also called as expiratory valve, pressure relief valve, pop off valve, Heidbrink valve, Dump valve, Exhaust valve, Spill valve. Ex:- Spring loaded disc and Stem and seat type of valve Spring Loaded Disc  Most commonly used type. Has 3 ports –Inlet, The Patient & Exhaust Port.  Exhaust port may be open to atmosphere or scavenging system
  13. 13. Adjustable Pressure Limiting Valve (APL Valve) Parts of Spring Loaded Disc 1. Female taper 2. Retaining screw 3. Stem with disc 4. Spring 5. Valve tap
  14. 14. Uses of APL valves in spontaneous & controlled ventilation Spontaneous • Valve is kept fully opened. • Partial closing will result in CPAP. • Pressure <1cm H₂O needed to open valve. Controlled • Valve is partially left open.
  15. 15. Classification of Breathing Systems
  16. 16. Classification of Breathing Systems Dripps et al classified them as Insufflation , open , semiopen , semiclosed and closed taking into account the presence or absence of  Reservoir  Rebreathing  Co2 absorption  Directional valves Collins divided breathing system into four broad groups depending on whether • the ambient (atmosphere) air is allowed to enter the system -open or semiopen • and/or the system allows gases from it to enter the ambient (atmosphere)- semiopen or semiclosed.
  17. 17. Classification of Breathing Systems Open System– • Anaesthetic gases are delivered directly into the patient’s airways • Atmospheric air acts as diluent • Patient’s airways has access to the atmosphere during both inspiration and expiration • No reservoir • No rebreathing • No neutralization of CO2 • No unidirectional valves Example 1. Nasal cannula 2. An open ether mask held away from the patient’s face
  18. 18. Classification of Breathing Systems Semi Open System– • Patient’s respiratory system is open to atmosphere both during inspiration and expiration through a reservoir that is open to atmosphere • Atmospheric air either carries or dilutes the anaesthetic agents • Gas reservoir present • No rebreathing • No neutralization of CO2 • No unidirectional valves • Fresh gas flow exceeds minute ventilation Examples include 1. Open ether mask held in close proximity to the face 2. ayre's T-piece with no expiratory limb or expiratory limb capacity less than tidal volume of the patient where air dilution occurs
  19. 19. Classification of Breathing Systems Semi Closed • Patient’s respiratory system is completely closed to atmosphere on inspiration but partly or fully open to atmosphere on exhalation • A reservoir is not open to atmosphere • Rebreathing may or may not be present Example 1. Mapleson rebreathing systems 2. Circle absorber with APL valve open allowing venting of gases 3. Water’s to and fro system
  20. 20. Classification of Breathing Systems Closed system • No access to atmosphere either on inspiration or exhalation • No escape of anaesthetic agent is allowed • Rebreathing is complete • Reservoir is present • CO2 absorber is present • unidirectional valve Example 1. Circle system with APL valve completely closed
  21. 21. Classification of Breathing Systems Conway classified the breathing system functionally according to method used for CO2 elimination  Breathing system with CO2 absorber  Breathing system without CO2 absorber
  22. 22. Breathing system without CO₂ absorption Breathing system with CO₂ absorption Unidirectional flow 1. Non-rebreathing Valve. Unidirectional Flow • Circle system with Absorber Bi Directional Flow a) Afferent Reservoir Systems • Mapleson A • Mapleson B • Mapleson C • Lack`s system b) Enclosed Afferent Reservoir Systems • Millers (1988) c) Efferent Reservoir Systems • Mapleson D • Mapleson E • Mapleson F & • Bain`s system. d) Combined Systems • Humphrey ADE Bi directional flow •To & Fro System
  23. 23. Breathing systems without CO2 absorber 1) Unidirectional flow • Non Rebreathing System • They make use of non-rebreathing valves. • To prevent rebreathing FGF =MV.
  24. 24. Non Rebreathing System These systems are not very popular because 1. Fresh gas flow has to be constantly adjusted and is not economical. 2. There is no humidification of inspired gases. 3. There is no conservation of heat 4. The valve is bulky and has to be placed close to the patient. 5. Malfunctioning of the valve can occur due to condensation of moisture. 6. Can be noisy at times. 7. Cleaning and sterilization is somewhat difficult
  25. 25. Bi Directional Flow without CO2 absorption For better understanding of functional analysis they have been classified as 1)Afferent Reservoir System (ARS) 2) Enclosed Afferent Reservoir System 3) Efferent Reservoir System 4) Combined System The efficiency of a system is determined in terms of CO₂ elimination & FGF utilization.
  26. 26. Bi Directional Flow without CO2 absorption • Afferent limb is that part of the breathing system which delivers the fresh gas from the machine to the patient. • If the reservoir is placed in this limb as in Mapleson A, B, C and Lack’s systems they are called as afferent reservoir system. • Efferent limb is that part of the breathing system which carries the expired gas from the patient and vents it to the atmosphere through the expiratory valve/port. • If the reservoir is placed in this limb as in Mapleson D, E, F and Bain systems they are called efferent reservoir system
  27. 27. MAPLESON BREATHING SYSTEM • In 1954 –Mapleson collected the existing breathing systems; analyzed and classified the Breathing systems.
  28. 28. Mapleson postulates (1954) Mapleson had analyzed these bi-directional flow systems & few basic assumptions have been made which are of historical interest. • Gases move En-bloc i.e. they maintain their identity as fresh gas, dead space gas & alveolar gas. There is no mixing of these gases. • Reservoir bags continues to fill up, without offering any resistance till it is full.
  29. 29. • The expiratory valve opens as soon as the reservoir bag is full & pressure inside the system goes above the atmospheric pressure. • The valve remains open throughout the expiratory phase without offering any resistance to gas flow & closes at the start of next inspiration.
  30. 30. Mapleson A (Magill‘s) System
  31. 31. Mapleson A (Magill‘s) System • The Mapleson A system was designed by Sir Ivan Magill in the 1930 • The Mapleson A or Magill system is good for spontaneous breathing patients.
  32. 32. Mapleson A (Magill‘s) System • It consist of a three-way T-tube connected to the fresh gas outlet, a reservoir bag and a corrugated tube. • The other end of the reservoir tube is connected to the patient and a spring-loaded APL valve. • Corrugated rubber or plastic tubing: 110-130 cm in length. • Reservoir Bag at Machine end. • APL valve at the patient end.
  33. 33. Functional Analysis : Spontaneous FGF Dead space gas Alveolar gas
  34. 34. Functional Analysis : Spontaneous Rebreathing of alveolar gas can be prevented if the fresh gas flow = patient's minute ventilation. • However, the last gas to be washed out of the circuit is dead space gas, which consists of warmed and humidified fresh gas, and no CO2. If some rebreathing of this dead space gas is accepted, a flow approximating to around 70% of the minute volume can be used FGF is :- High –Force the dead space gas out. Intermediate –Some dead space gas will be retained in the system. Low –More alveolar gas will be retained.
  35. 35. Controlled Ventilation: First Breath Exhalation Next Inspiration
  36. 36. Mapleson A (Magill‘s) System Advantages • Best among all Mapleson’s systems for spontaneous ventilation • Minimal wastage of gases during spontaneous ventilation Disadvantages: • Not efficient for controlled ventilation. • Wastage of gases & operation theatre pollution. • Expiratory valve required –produces slight resistance during expiration. • Expiratory valve is heavy (Heidbrink valve). • Expiratory valve is near patient and inconvenient to use. • Not suitable for paediatric use.
  37. 37. Mapleson A – Lack Modification • A co-axial modification of the Mapleson A system. • Designed to facilitate scavenging of expired gas & make more efficient for controlled ventilation • 1.6 m in length • FGF through outside tube ( 30mm), exhaled gases from inner tube. • Inner tube wide in diameter (14 mm) to reduce resistance to expiration(1.6 cm H2O). • Reservoir bag at machine end • APL valve at machine end.
  38. 38. Mapleson A – Lack Modification • The Lack circuit is essentially similar in function to the Magill, except that the expiratory valve is located at the machine-end of the circuit, being connected to the patient adapter by the inner coaxial tube.
  39. 39. Mapleson A – Lack Modification Advantages • The location of the valve is more convenient, facilitating intermittent positive pressure ventilation and scavenging of expired gas. Disadvantages • In common with other co-axial systems, if the inner tube becomes disconnected or breaks, the entire reservoir tube becomes dead-space. • This can be avoided by use of the 'parallel Lack' system, in which the inner and outer tubes are replaced by conventional breathing tubing and a Y-piece.
  40. 40. TESTING FOR LEAKS/MAGILL A) To attach a tracheal tube to the inner tubing at the patient end of the system. Blowing down the tube with the APL Valve closed will produce movement of the bag, if there is a leak between the two limbs. B) To occlude both limbs at the patient connection with the APL Valve open & then squeeze the bag. Leak in the inner limb, gas will escape through the APL Valve & the bag will collapse.
  41. 41. Enclosed Afferent Reservoir Systems
  42. 42. Enclosed Afferent Reservoir (EAR) Systems • Coaxial version • Non coaxial version
  43. 43. Enclosed Afferent Reservoir (EAR) Systems • The Enclosed Afferent Reservoir (EAR) is described by Miller. • It consists of Mapleson A system enclosed within a non distensible structure • It is also constructed by enclosing the reservoir bag alone in a bottle and connecting the expiratory port to the bottle with a corrugated tube and a one-way valve. • To the bottle is also attached a reservoir bag and a variable orifice for providing positive pressure ventilation
  44. 44. Enclosed Afferent Reservoir (EAR) Systems ADVANTAGES 1. This system provides selective elimination of alveolar gas in both spontaneous and controlled ventilation 2. A comparison with Bain’s circuit in controlled ventilation demonstrated greater efficiency in eliminating CO2. A FGF of 70ml/kg/min using EAR system gave minimal hypocarbia which equated to a FGF of 100ml/kg/min using a Bain’s system. 3. More efficient than Bain for controlled ventilation.
  47. 47. MAPLESON B SYSTEM • 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 retained fresh gas and alveolar gas is inhaled. • Rebreathing is avoided with fresh gas flow rates of greater than twice the minute ventilation for both spontaneous and controlled ventilation.
  50. 50. MAPLESON C SYSTEM • This circuit is also known as Water’s circuit. • This circuit is sometimes used in portable ventilators. • It is similar in construction to the Mapleson B , but the main tube is shorter. • A FGF equal to twice the to minute ventilation is required to prevent rebreathing. • CO2 builds up slowly with this circuit. • Mapleson B &C : In order to reduce rebreathing of alveolar gas FG entry was shifted to near the patient. • This allows a complete mixing of FG and expired gas. • The end result is that these system are neither efficient during spontaneous nor during controlled ventilation.
  52. 52. MAPLESON D SYSTEM • It consists of fresh gas inlet nearer the patient end , a corrugated rubber tubing one end which is connected with expiratory valve and then reservoir bag. • It is mainly used for assisted or controlled ventilation
  53. 53. Bain system (Mapleson D)
  54. 54. Bain system (Mapleson D) • It was introduced by Bain and Spoerel in 1972 • It is a modification of Mapleson D system. • It is a coaxial system in which fresh gas flows through a narrow inner tube within outer corrugated tubing
  55. 55. Bain system (Mapleson D) Specifications:- • Length-1.8 meters. • Diameter of outer tube-22mm(transparent, carries expiratory gases) • Diameter of inner tubing-7 mm(inspiratory) • Resistance-Less than 0.7 cm H2O • Dead space-Outer tube upto expiratory valve( around 500ml=TV) • Flow settings- For controlled ventilation < 10kg 2L/min 10-50 kg 3.5L/min >60kg 70ml/kg For spontaneous ventilation 200-300ml/kg
  56. 56. Bain system (Mapleson D)- Functional Analysis
  57. 57. Bain system (Mapleson D)- Functional Analysis Spontaneous respiration: • The breathing system should be filled with FG before connecting to the patient. • When the patient takes an inspiration, the FG from the machine , the reservoir bag and the corrugated tube flow to the patient.
  58. 58. Bain system (Mapleson D)- Functional Analysis controlled
  59. 59. Bain system (Mapleson D)- Functional Analysis • Controlled ventilation : • To facilitate intermittent positive pressure ventilation, the expiratory valve has to be partly closed so that it opens only after sufficient pressure has developed in the system. • When the system is filled with fresh gas, the patient gets ventilated with the FGF from the machine, corrugated tubing and the reservoir bag.
  60. 60. Bain system (Mapleson D) Factors governing concentration of Inspired Mixture in Mapleson D system • FGF rate • Respiratory rate • Expiratory pause • Tidal volume
  61. 61. Bain system (Mapleson D) • In spontaneous breathing only FGF can be manipulated. Hence it has to be 2 to 4 times the patient’s minute ventilation(200 -300ml/kg) to minimize rebreathing of exhaled alveolar gases. • In controlled breathing, these factors can be totally manipulated. So using low respiratory rate, long expiratory pause and high tidal volume most of the fresh gas(70ml/kg) could be used for alveolar ventilation without wastage.
  62. 62. ADVANTAGES OF BAIN'S SYSTEM • Light weight. • Minimal drag on ETT as compared to Magill's circuit. • Low resistance. • As the outer tube is transparent, it is easy to detect any kinking or disconnection of the inner fresh gas flow tube. • It can be used both during assist and controlled ventilation . • It is useful where patient is not accessible as in MRI suites. • Exhaled gases do not accumulate near surgical field, so risk of flash fires is abolished. • Easy for scavenging of gases as scavenging valve is at machine end of the circuit. • Easy to connect to ventilator. • There is some warming and humidification of the inspired fresh gas by the exhaled gas present in outer tubing.
  63. 63. DISADVANTAGES OF BAIN'S SYSTEM • Due to multiple connections in the circuit there is a risk of disconnections. • Wrong assembling of the parts can lead to malfunction of the circuit. • Theatre pollution occurs due to high fresh gas flow. However, it can be prevented by using scavenging system. • Increases the cost due to high fresh gas flows. • There can be kinking of the inner tube blocking the fresh gas supply leading to hypoxia • There can be crack in the inner tube causing leakage • It cannot be used in paediatric patients with weight less than 20 kg.
  64. 64. Checking the Bain’s circuit 1)Pethicks test - To check the integrity of the inner tube • Flush high flow into the circuit and occlude the patient end until the reservoir bag is filled • The patient end is then opened and circuit is then flushed with oxygen • If inner tubing is intact, the venturi effect occurs at the patient end, causing decrease in pressure within the circuit and bag will deflate • If there is leak in inner tubing, fresh gas will escape in the expiratory limb and the bag will inflate
  65. 65. Checking the Bain’s circuit • For checking integrity of inner tube of Bain’s system, a test is performed by setting a low flow on the oxygen flowmeter and occluding the inner tube with a finger or barrel of a small syringe at the patient end while observing the flow meter indicator. If the inner tube is intact and correctly connected, the indicator will fall due to back pressure. • Integrity of APL valve and scavenging system: By occluding the patient end and closing the APL valve the system is pressurized. The APL valve is then opened. The bag should deflate easily if the valve is working properly. • Integrity of outer tubing:Wet the hands with spirit. Blow air through the tube. Wipe the tube with wet hands. Leak will produce chillness in the hands.
  66. 66. Mapleson E OR Ayre's T- PIECE
  67. 67. Mapleson E OR ayre's T- PIECE
  68. 68. Mapleson E OR ayre's T- PIECE • Introduced by Phillips Arye in 1937. • Belongs to Mapleson E. • Available as metallic / plastic. • Length-5cm and Diameter-1cm. • Parts – inlet, outlet, side tube.
  69. 69. Mapleson E OR ayre's T- PIECE • Fresh gas enters the system through the side arm • One end of the body is connected to the patient(apparatus dead space) and the other end is connected to the tubing which acts as reservoir • This system is suited in neonates and infants in whom expiratory valve would produce significant resistance
  70. 70. Mapleson E OR ayre's T- PIECE Spontaneous breathing Inspiration:  Since the peak inspiratory flow rates are higher than FGF, gases are dawn from the reservoir limb.  If the reservoir limb capacity is less than the tidal volume of the patient then air dilution occurs, converting the semiclosed system into semiopen system as per Collin’s classification.
  71. 71. Mapleson E OR ayre's T- PIECE Exhalation:  Both exhaled and FGF pass into the reservoir limb and then to the atmosphere. End Expiratory Pause:  FGF flushes out and fills the reservoir limb with fresh gases pushing out the exhaled gases.  If the reservoir limb capacity is more than the tidal volume of the patient and FGF are less than rebreathing occurs
  72. 72. Harrison modification of ayre's T- PIECE Harrison reviewed modifications of T-piece in relation to the capacity of the reservoir(expiratory limb) and classified T-piece system into 3 categories  Type I – No expiratory limb  Type II – Volume of expiratory limb greater than the patient’s tidal volume  Type III - Volume of expiratory limb lesser than the patient’s tidal volume He concluded that the most useful was Type II
  73. 73. Mapleson E OR ayre's T- PIECE Factors to be considered for Spontaneous Breathing • Diameter of reservoir must be sufficient to have lowest possible resistance. • Volume of reservoir limb(RV) should not be less than the patient’s tidal volume(TV) • If RV=TV , then FGF=2.5 times minute ventilation is required to prevent air dilution • If RV is less than TV, then FGF has to be increased further, otherwise air dilution can occur • If RV=0 (no expiratory limb) than TV, then FGF should be atleast equal to the peak inspiratory flow rate of the patient to prevent air dilution
  74. 74. Mapleson E OR ayre's T- PIECE WORKING : Controlled Ventilation • It is done by intermittently occluding the reservoir limb by thumb. • Neither air dilution nor rebreathing can ever occur.
  75. 75. Mapleson E OR ayre's T- PIECE WORKING : Controlled Ventilation ADVANTAGES • Low resistance • Low dead space • No valves so easy to use DISDADVANTAGES • Barotrauma • No feel of the bag • No APL valve so no pressure buffering effect of the bag • Difficult to scavenge
  76. 76. Mapleson F OR Jackson-Rees Modification of Ayre's T- PIECE
  77. 77. Mapleson F OR Jackson-Rees Modification of ayre's T- PIECE • It is a modification of Mapleson E by Jackson Rees and is known as Jackson Rees modification. • It has a 500 ml bag attached to the expiratory limb. • This bag helps in respiratory monitoring or assisting the respiration. • It also helps in venting out excess gases. • The bag has a hole in the tail of the bag that is occluded by using a finger to provide pressure. • The bags with valve are also available. • It is used in neonates, infants, and paediatric patients less than 20 kg in weight or less than 5 years of age.
  78. 78. Mapleson F OR Jackson-Rees Modification of ayre's T- PIECE
  79. 79. Mapleson F Breathing System Technique of use • It also functions like Mapleson D system. • The flows required to prevent rebreathing are 2 - 3 times minute volume during spontaneous ventilation. • The flows required to prevent rebreathing are 1000 + 100ml/kg during controlled ventilation.
  80. 80. Mapleson F Breathing System For spontaneous respiration:  The relief mechanism of the bag is left fully open. The pattern and rate of breathing Small movements of the bag demonstrate the pattern and rate of breathing. For controlled respiration: Inspiration:  The hole in the bag can be occluded partially or completely by the user during inspiration and ventilation is done by squeezing the bag. Expiration:  The open end is released to allow the gas in the system to escape
  81. 81. Mapleson F Breathing System ADVANTAGES 1. Simple and easy to assemble 2. Light weight 3. Portable 4. No valves 5. Least resistance 6. Suitable for paediatric patients 7. Inexpensive 8. Effective for both controlled and spontaneous ventilation
  82. 82. Mapleson F Breathing System DISADVANTAGES 1. Wastage of gases 2. It lacks humidification 3. Barotrauma – occlusion of relief valve can increase airway pressure producing barotrauma
  83. 83. BREATHING SYSTEM ( MAPLESON) SPONTANEOUS CONTROLLED A 1.5 – 2 x M.V 2-5 x M.V D 2 - 4 x M.V 70ml/kg/min F 2 - 3 x M.V 1000ml + 100ml/kg/min TO PREVENT REBREATHING IN THE BREATHING UNIT
  84. 84. Combined System HUMPHREY A D E System
  85. 85. Combined System • Humphry ADE: with two reservoirs one in afferent and one in efferent limb • System can be changed from ARS to ERS by changing the position of the lever. • Can be used for adults and children.
  86. 86. Combined System
  87. 87. Humphrey ADE Circuit 1
  88. 88. Humphrey ADE Circuit 2
  89. 89. Breathing Systems with CO2 Absorption
  90. 90. Breathing Systems with CO2 Absorption Components of Circle System 1. Fresh gas entry, 2. Two unidirectional valves, 3. Sodalime canister 4. Y-piece to connect to the patient, 5. Reservoir bag 6. A relief valve and 7. Low resistance interconnecting tubing.
  91. 91. Breathing Systems with CO2 Absorption • The FGF should enter the system proximal to the inspiratory unidirectional valve. • There should be two unidirectional valves on either side of the reservoir bag and the canister, • Relief valve should be positioned in the expiratory limb only, 3 Essential Factors
  92. 92. Breathing Systems with CO2 Absorption
  93. 93. • Let us start adding parts to our circle, in a step by step way.. • A circle is added to the patient.
  94. 94.  However, though we have connected the patient to the circle, he will unfortunately not be able to breath in or out from it. This is because the circular tube is made of a non stretchable material and therefore it cannot expand to accept the patient's expiration, and nor can it contract when the patient tries to inspire from it.
  95. 95. To allow the patient to breath in and out, we attach a flexible bag ( called reservoir bag ) to the circle system. Now the patient can breath, through the tubes, into and out of the flexible reservoir bag.
  96. 96.  However, if we leave our patient like this, he will not survive, since we are forgetting to give him something vital for life. We need to urgently give our patient oxygen !  The oxygen (and other gases) come out of the flow meters of your anaesthetic machine. The flow meters allow you to control the flow of the various gases that you supply to your patient. The total flow of gases coming out of the flow meters is called " total fresh gas flow" or more commonly , simply referred to as, "fresh gas flow".
  97. 97. So, to keep our patient alive, we supply fresh gas flow ( containing oxygen, shown as blue dots ) from the flow meters into the circle system
  98. 98.  We " force " the patient to inspire from one part of the circle, and expire into the other part of the circle, using what are called “one way valves”. As their name suggests, these valves allow gas to pass one way, and not the other way. The valve has a disc that opens only in one direction, allowing gases to only go in that direction. In the example below, the one way valve is designed to allow flow in the direction of the green arrow and not allow flow to go in the opposite direction..  We add two one way valves into the circle system as shown below. One allows flow only towards the patient and the other allows flow only away from the patient.
  99. 99.  During inspiration, the valve labeled " expiratory one way valve " closes, preventing the patient from inspiring the gases he just breathed out. On the other side, the valve labeled " inspiratory one way valve opens, letting the patient inspire gases rich with oxygen. The tubing from the inspiratory one way valve to the patient carries only inspiratory gases, and we can therefore call it the “inspiratory tubing”.
  100. 100.  During expiration, the reverse happens. The inspiratory one way valve closes, preventing the expired gases going into the inspiratory tubing. Instead, the valve labeled "expiratory one way valve" opens, letting expired gases go via the tubing between it and the patient. The tubing between the patient and the expiratory one way valve carries only expired gases, so we can therefore call it the “expiratory tubing”.
  101. 101.  However, we discover another problem. We find that the reservoir bag is mysteriously getting bigger and bigger.  Ultimately the reservoir bag will burst.
  102. 102.  It would not be very pleasant to have reservoir bags bursting every few minutes, so we need a solution. The answer is to add an “pressure limiting outflow valve” to the circle. This valve has a disc that is designed to open when a positive pressure develops on one side of it, thereby letting any excess gas to flow out and prevent further rises of pressure.
  103. 103. During inspiration, the pressure in the system is low, so the pressure limiting outflow valve remains closed.
  104. 104.  Now our patients breathes out. During early expiration, the expired gases go into the reservoir bag. Because the pressure is low, the pressure limiting outflow valve remains closed.
  105. 105. The expiratory gases fill the reservoir bag till it is fully distended. Once the bag is fully distended, the expired gases have nowhere to go and the pressure in the circle system rises.  The rise in pressure causes the pressure limiting outflow valve to open, releasing the excess gases (grey arrow ) out of the circle system. In this way, the pressure limiting outflow valve lets excess gas escape and prevents a rise in the circle system pressure.
  106. 106.  Now that our patient can inspire and expire nicely. we can ask the question; “Is he happy ?” The answer unfortunately is “No”. The reason the patient is not happy is that he is inspiring his own carbon dioxide ( shown as grey dots ).
  107. 107. Let us include a CO2 absorber into our circle system. Now as the patient inspires, the CO2 containing gas from the reservoir bag passes through the CO2 absorber. The absorber "absorbs" the CO2, making the inspired gas CO2 free
  108. 108.  You need to give the patient anaesthetic gases to keep him asleep. We do this by adding anaesthetic vapours (yellow dots ) to the fresh gas flow using a vaporizer.
  109. 109. Optimization of Circle Design • Unidirectional Valves • Close to patient to prevent backflow into inspiratory limb if circuit leak develops. • Fresh Gas Inlet • Placed between absorber & inspiratory valve. If placed downstream from inspiratory valve, it would allow FG to bypass patient during exhalation and be wasted. FG placed between expiration valve and absorber would be diluted by recirculating gas
  110. 110. Optimization of Circle Design APL valve • Placed immediately before absorber to conserve absorption capacity and to minimize venting of FG Breathing Bag • Placed in expiratory limb to decrease resistance to exhalation. Bag compression during controlled ventilation will vent alveolar gas thru APL valve, conserving absorbent
  111. 111. Circle system can be: • closed (fresh gas inflow exactly equal to patient uptake, complete rebreathing after carbon dioxide absorbed, and pop- off closed) • semi-closed (some rebreathing occurs, FGF and pop-off settings at intermediate values), or • semi-open (no rebreathing, high fresh gas flow)
  112. 112. Anesthesia Breathing Systems • Circle systems – Most commonly used – Adult and child appropriate sizes – Uses chemical neutralization of CO2 – Conservation of moisture and body heat – Allows for mechanical ventilation of the lungs using the attached ventilator – Allows for adjustment of ventilatory pressure – Is easily scavenged to avoid pollution of OR environment – Low FGF’s saves money
  113. 113. Anesthesia Breathing Systems • Advantages of rebreathing – Cost reduction (use less agent and O2) – Increased tracheal warmth and humidity – Decreased exposure of OR personnel to waste gases – Decreased pollution of the environment
  114. 114. Disadvantages of Circle System • Greater size, less portability • Increased complexity – Higher risk of disconnection or malfunction. • Difficulty of predicting inspired gas concentration during low fresh gas flow
  118. 118. WATER’S TO AND FRO ABSORPTION SYSTEM  The patient breathes to and fro from a reservoir bag, which is connected to the facemask or endotracheal tube via canister soda lime.  The system used is Mapleson C system with placement of sodalime canister between the reservoir bag and FGF port.  The Fresh gases are introduced at the patient end of the system.  Exhaled carbon dioxide is absorbed by the soda lime.  Excess gas is vented when necessary via the APL valve.
  119. 119. WATER’S TO AND FRO ABSORPTION SYSTEMADVANTAGES 1. Inexpensive 2. Portable 3. Economy with low flow of oxygen, nitrous and volatile agents 4. Reduction of operating room pollution 5. Conservation of heat and humidity
  120. 120. WATER’S TO AND FRO ABSORPTION SYSTEMDISADVANTAGES 1. Cumbersome 2. The soda lime near the patient end become more rapidly exhausted , leading in insufficiency in soda lime use and a progressive increase in apparatus dead space. 3. Channeling of gas can lead to rebreathing of gases 4. Expiratory valve position near the patient end is a major inconvenience 5. Risk of pt. inhaling sodalime. 6. Danger of extubation bcz of weight and proximity to the pt.
  121. 121. THANK YOU