Final circuits

breathing circuits

1. Circuits Presenter Moderator Dr. Pooja Lama Associate Prof. Dr. U. B. Bajracharya Resident Anesthesiology

2. Objectives Definitions History of breathing system Classification of breathing systems Working principles of breathing systems Components of breathing system Conclusion

3. Definition Assembly of components which connects the patient airway to the anaesthetic machine creating an artificial atmosphere , from and into which the patients breathes .

4. Function To deliver oxygen and other gases to the patient and to eliminate carbon dioxide.

5. History 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 In 1926, Brian Sword introduced the circle system. Ayre’s T piece was introduced in 1937 by Phillip Ayre Modified by Jackson Rees into Mapleson F in 1950 by adding 500ml of reservoir bag Bain circuit was introduced in 1972 by Bain and Spoerel .

6. Classification McMohan in 1951 Open  no rebreathing Semi closed  partial rebreathing Closed  total rebreathing

7. Dripps classification Insufflation Open Semi open Semi closed Closed Schimmelbush mask Yankeur mask

8. Conway classification Breathing systems with CO2 absorber Breathing systems without CO2 absorber Miller Classification Breathing system without CO2 absorber Breathing system with CO2 absorber Unidirectional flow: Non-rebreathing valve Unidirectional flow: Circle system with absorber Bi-directional flow: a) Afferent Reservoir systems Mapleson A, B, C and Lack b) Efferent Reservoir system Mapleson D, E , F and Bain c) Combined system Humphrey ADE Bi-directional flow: To & Fro system

9. Disadvantages of insufflation and open Poor control of inspired gas concentration poor control of depth of anesthesia Pollution of operating room with large volumes of waste gas Mechanical drawbacks during head and neck surgery.

10. Anesthetic breathing circuit classification: On the basis of use of carbon-dioxide absorber:- do not use an absorber use an absorber MAPLESON SYSTEM CIRCLE SYSTEM Circle system is the most common breathing circuits used for anesthetic delivery

11. Criteria for anesthetic breathing circuit Low resistance conduit for gas flow A reservoir for gas that can meet the patient’s inspiratory flow demand An expiratory port or valve to vent excess gas. Have minimal apparatus dead space.

12. Mapleson’s classification of breathing system Mapleson in 1954 described and analyzed five different breathing circuits. (A, B, C, D, E) Willis in 1975 described the F system. Similar to circle breathing system that they accept a fresh gas flow , supply sufficient volume of gas and eliminate carbon-dioxide . Differ from circle system that they have bidirectional flow and do not use an absorber.

13. Components of Mapleson Patient end to a facemask or endotracheal tube Breathing corrugated tubes Fresh gas inlet Adjustable pressure limiting valve Reservoir bag

14. Different types of M apleson

15. Three distinct functional groups can be seen: Functional groups Gas stored in reservoir bag Named as A Fresh Gas Afferent reservoir system BC Mixed inspired and expired gas Junctional reservoir system DEF Mixed expired gas Efferent reservoir system

16. Relative efficacy of M apleson system During spontaneous ventilation: A>DFE>CB During controlled ventilation: DFE>BC>A

17. Mapleson A Mapleson A is also called as Magill circuit It is best for spontaneous ventilation. Modification of Magill circuit is called as Lack’s circuit. Mapleson A has a corrugated breathing hose of length 110 cm with an internal volume of 550ml.

18. Working principle: Mapleson A:- Spontaneous ventilation Breathing bag fills with FGF in first inspiration. Pt inspires the gases so the reservoir bag becomes partially empty Exhale:- gases from both ends enter bag and once it is full the exhaled gases pass out through APL valve End-expiratory pause: FGF now drives the exhaled gases out.

19. Inspiration: manual squeezing though APL valve is closed some of FGF will go out. Since bag is completely empty, now on expiration the exhaled gases will reach the bag and get mixed. But bag is not yet full enough to open the APL valve. On next inspiration: on squeezing  APL valve opens and exhaled gases pass out as well they are inhaled so rebreathing occurs. Working principle: Mapleson A:- Controlled ventilation

20. Mapleson B and C Mapleson B:- FGF should be 2-2.5 times the minute ventilation. Mapleson c (Bagging system)

21. Inspiration: FGF fills the bag and hose and as respiratory rate is higher than FGF rate so the bag get emptied. Expiration: exhaled gas get mixed with FGF and reach bag. When bag is full: exhaled gases pass out of APL valve, first anatomical dead space then alveolar gas. Next inspiration: rebreathing occurs. Working principle: Mapleson D:- Spontaneous ventilation

22. Inspiration: manual squeezing FGF goes to patient as well pass out of APL. Expiration: partially emptied bag gets filled with exhaled gas + FG. Expiratory pause: FGF pushes the exhaled gases towards bag  gets full APL opens dead space then alveolar gas. Next inspiration: pt inspired FGF + mixed gas and on squeezing the exhaled gases again pass out of APL. Working principle: Mapleson D: Controlled ventilation

23. Mapleson E and F During inspiration  inspiratory drive is more than FGF rate so some gases are drawn from the reservoir limb. During expiration both the exhaled air and fresh gas continue to pass towards limb and voided to atmosphere D. During end expiratory pause FGF fills the limb.

24. Modifications Lack system Modification of Mapleson A Inner expiratory and outer inspiratory. length Bain circuit Modification of Mapleson D Inner inspiratory and outer expiratory. Pethick test

25. Bain circuit . Coaxial circuit and modification of M apleson D Outer tube 22 mm diameter. 1.8 m long Fresh gas flow to patient end via thinner coaxial inside the expiratory tube Fresh gas inflow rate necessary to prevent rebreathing is 2.5 times minute ventilation

26. Isopleth Vf - Fresh gas flow rate ml/kg/min Ve - minute ventilation ml/kg/min When FGF is high  PACO2 becomes ventilation dependent. When minute volume exceeds the FGF PACO2 is dependent on FGF.

27. Advantages of B ain circuit Lightweight, convenient, easily sterilized and reusable. Very low resistance to breathing. Scavenging of gases from the expiratory valve is facilitated because the valve is located away from the patient. Exhaled gases in the outer reservoir tubing add warmth to the inspired fresh gases by countercurrent heat exchange .

28. Disadvantages of Bain circuit Unrecognized disconnection and kinking of the inner fresh gas tube. An obstructed antimicrobial filter positioned between the Bain circuit and the endotracheal tube can result in increased resistance in the circuit . High flow gas rate  wastage of gas. Pethick test Outer tube is transparent

29. Test for Bain’s circuit Pethick test Foex Crempton Smith test Close the APL valve and allow reservoir bag to fill completely Now press oxygen flush Reservoir bag collapses if inner tube is intact Because oxygen delivered at high flow through inner tube will drag all the air present in the outer tube due to its venturi effect. Close the APL valve and turn on oxygen at 2 L/minute End of inner tube is occluded If inner tube is intact then bobbin will descend slightly Once released it will ascend to its original place.

30. Required fresh gas flow

31. Advantages of Mapleson system Equipment is simple, inexpensive and rugged. Variations in minute volume affect end tidal CO2 less than circle system. Are lightweight and not bulky. Easy to position conveniently . Changes in fresh gas concentrations result in rapid changes in inspiratory gas composition.

32. Disadvantages of M apleson system These system require high gas flows. Because of high fresh gas flow, inspired heat and humidity tend to be low. In mapleson A, B and C the APL valve is located close to patient , where it may be inaccessable to the user. Mapleson E and F are difficult to scavange .

33. Circle system

34. Circle system It is so named because :- it allows circular, unidirectional gas flows Facilitated by unidirectional valves It must allow for spontaneous ventilation, manual ventilation and positive pressure ventilation.

35. Circle system

36. Three Essential factors There should be:- Two unidirectional valves on either side of reservoir bag and canister. Pop off valve or APL valve should be positioned in the expiratory limb only. The Fresh Gas Flow should enter the system proximal to the inspiratory unidirectional valve.

37. Low Flow Anesthesia To enhance oxygen and anaesthetic uptake and the excretion of nitrogen (N 2 ), a high FGF is recommended at the start of an anaesthetic . When clinically desirable concentrations are reached , the FGF can be reduced, to a basal metabolic oxygen consumption rate of approximately 250 ml min −1 . Hence in circle system, low flow upto 250ml/min to 500ml/min can be administered.

38. Advantage of circle system Maintenance of relatively stable inspired gas concentrations Conservation of respiratory moisture and heat Elimination of carbon dioxide An economy of anesthetic gases resulting:- from rebreathing as FGF could be reduced to as low as 250-500ml of oxygen 5. Prevention of operating room pollution.

39. Disadvantage of circle system Leaks and disconnections Misconnections Occlusion Malfunction of unidirectional valves

40. Components of circle system Fresh gas inflow source Inspiratory and expiratory unidirectional valves Inspiratory and expiratory corrugated tubes Y piece Overflow or adjustable pressure limiting valve Reservoir or breathing bag Canister containing carbon-dioxide absorbent.

41. Unidirectional valves. Essential element . Incompetence is one the most common problem

42. Adjustable pressure limiting valve It is operator-adjustable relief valve that vents excess breathing circuit gases to the scavenging system. Other common names are “pop off” valve and pressure relief valve. Types:- 1. variable- resistor or variable-orifice type 2. pressure-regulating type Modern machines

43. APL valve with inbuilt overpressure safety devices When unscrewed:- Outer valve opens when exhaled gases create a pressure of 1.5cm H20 Valve is closed (fully screwed) Valve is fully screwed so an excess pressure needed to open the valve. At 30 cm H2O valve begins to open. At 60-70 cm H2O valve is fully open.

44. Anesthetic reservoir bag Breathing Bag. Capacity:- 500ml, 1L or 2L. Pressure standards:- Minimal pressure  30 cm H2O Maximal pressure  60 cm H2O

45. Functions of reservoir bag Serves as reservoir for exhaled gases and excess fresh gas. Means of delivering manual ventilation Serves as visual and tactile means of monitoring spontaneous breathing effort Partially protecting the patient from excessive positive pressure on inadvertent closure of APL valve.

46. Fresh gas decoupling During inspiration:- FGF is diverted to reservoir bag by the decoupling valve

47. Fresh Gas Decoupling During Expiratory phase:- decoupling valve opens  FG in reservoir bag is drawn towards circle system to refill piton chamber ventilator. Since ventilator exhaust valve is also open exhaled gases and excess FG passes to the scavenging system.

48. Corrugated breathing circuit tubing The hoses should have a diameter that provided low resistance to gas flow to provide laminar flow. Adults:- 22mm Pediatrics:- 15 mm Should be flexible so that kinking does not occur. Corrugated so as to adjust the length of tube. Light weight.

49. Carbon-dioxide absorbers Ideal carbon-dioxide absorbents:- Lack of reactivity with common anesthetics Absence of toxicity Low resistance to airflow Minimal dust production Small cost Ease of handling High efficiency carbon dioxide absorption

50. Absorber canister Transparent  to monitor the absorbent for its presence and colour . The absorbent should be changed when the colour change is about 50 to 70%.

51. Chemistry of Absorbents Most commonly used is Soda-Lime Absorbent Ca (OH)2 H2O NaOH KOH Soda lime 80% 16% 3% 2% CO2 + H2O H2CO3 H2CO3 +2HaOH (KOH) Na2CO3 (K2CO3) +H2O + heat Na2CO3 (K2CO3) + Ca (OH)2 CaCO3 + 2NaOH(KOH) +Heat

52. Some of carbon dioxide abosorbers : Absorbent Ca (OH)2 % LiOH % H2O% NaOH % KOH % Other% Classic soda lime 80 16 3 2 -- Baralyme 73 11-16 5 11 Ba(OH) New soda lime 73 19 <4 -- Spiralith 95 <5 Polyethylene

53. Indicators Fresh soda lime has pH = 12. D ecreases as CO2 is absorbed. Indicators:- W hite Soda lime contains ethyl violet, critical pH = 10.3 ; purple Pink Soda lime contains phenolphthalein, critical pH= 7. colourless .

54. Carbon dioxide removal capacity 100 grams of soda lime granules absorb around 14-23 liters of CO2 . If completely reacted:- A pound of calcium hydroxide has the capacity to absorb 0.59 lb of carbon dioxide A pound of Lithium hydroxide has the ability to absorb 0.91 lb of carbon dioxide.

55. Factors affecting carbon dioxide removal capacity The amount of surface area of the absorbent to which the exhaled gas is exposed, The intrinsic capacity of absorbent to remove carbon dioxide, The amount of functionally intact absorbent remaining in the absorber. Smaller the granule size greater the surface area so more absorption. BUT the airflow resistance is increased

56. Size of granule 4-8 mesh size  is the size at which absorptive surface area and resistance to flow are optimized. Mesh size refers to the number of openings per linear inch in a seive through which the granular particles can pass.

57. Problems with absorbents Formation of potentially harmful products:- 1. Compound A 2. Carbon monoxide 3.Dichloroacetylene Nephrotoxic Increased Carboxyhemoglobin Cranial nerve neuropathies and encephalitis Sevoflurane Desflurane , enflurane and isoflurane Trichloroethylene

58. B. Absorbent Heat Production:- Rare but potentially life-threatening complication which leads to fires and explosions due to extreme exothermic reactions.

59. Summary

60. Scavenging system Scavenging is collection and removal of the vented anesthetic gases from the operation theatre. Types: Active Passive Suction is applied Waste gases proceed passively down corrugated tubing through the room ventilation exhaust grill of operating room

61. Recent advances New soda lime  does not contain KOH Spiralyth  only Lithium hydroxide

62. Conclusion Most common used breathing system is circle system. Mapleson A for spontaneous ventilation Mapleson D for controlled ventilation. Modification of Mapleson A is Lack’s system. Mapleson D is Bain’s system. Mapleson E is Mapleson F. Test for Bain’s circuit  Pethick test and Foex Crempton Test

63. Thank you..

64. Reference Miller’s anesthesia 8 th edition Ward’s anesthetic equipments 6 th edition Morgan 5 th edition

65. Role of heat and humidification

66. Filter

67. Physics Hagen Pouesille law.

68. Apparatus dead space.

69. Recent advances New soda lime Limb – O circuit King Flex – 2

70. Humphrey ADE

71. THANK YOU..