Breathing systems

Introduction to Breathing Systems in Anaesthesia

1. Dr brijesh savidhan dept of anaesthesiology travancore medical college BREATHING SYSTEMS

2. What is a breathing system? An assembly of components that Connects the patient’s airway to the anesthesia machine Creating an artificial atmosphere from and into which the patient breathes .

3. Components A fresh gas entry port / delivery tube A reservoir for gas, in the form of a bag A port to connect it to the patient's airway; An expiratory port / valve Corrugated tubes for connecting these components.

4. Components A CO2 absorber if total rebreathing is to be allowed Flow directing valves may or may not be present Connectors and adapters Filters

5. Requirements Essential Desirable Deliver gases from machine to alveoli Eliminate CO2 Have minimal apparatus dead space Have low resistance Economy of fresh gas Conservation of heat Adequate humidification of inspired gas Light weight Convenient Efficient for both spontaneous and controlled ventilation Adapatable

6. Classification Unidirectional flow Unidirectional flow Bidirectional flow Bidirectional flow

7. Classification Without CO2 absorption With CO2 absorption Unidirectional flow Non rebreathing systems Circle systems Bidirectional flow Afferent reservoir systems Efferent reservoir systems Enclosed afferent reservoir Combined system Unidirectional flow Circle system with absorber Bidirectional flow To and fro system

8. Expiratory unidirectional valve Inspiratory unidirectional valve Non rebreathing systems Use non rebreathing valves Patient Fresh gas flow

9. Inspiration Spontaneous EUDV closes the expiratory port IUDV opens to allow gas flow into lungs Fresh gas flow Patient

10. Expiration Spontaneous IUDV opens returns back to position EUDV opens the expiratory port Fresh gas flow Patient

11. Non rebreathing systems No rebreathing Unidirectional flow The FGF should be equal to the minute ventilation of the patient. Disadvantages FGF has to be constantly adjusted and is not economical No humidification or heat conservation Bulk of valve near patient – inconvenient Valves malfunction due to moisture condensation Largely disappeared from anesthetic practice. The NRB valves are used in manual resuscitators

12. Classification Without CO2 absorption With CO2 absorption Unidirectional flow Non rebreathing systems Circle systems Bidirectional flow Afferent reservoir systems Efferent reservoir systems Enclosed afferent reservoir Combined system Unidirectional flow Circle system with absorber Bidirectional flow To and fro system

13. Afferent reservoir Efferent reservoir Enclosed afferent reservoir Combined Bi directional flow

14. Afferent Reservoir Systems The afferent limb is that part of the breathing system which delivers the FG from the machine to the pt. If the reservoir is placed in this limb, they are called afferent reservoir systems. Mapleson A, B, C

15. Efferent reservoir systems The efferent limb is that part of the breathing system which carries expired gas from the patient and vents it to the atmosphere through the expiratory valve/port. If the reservoir is placed in this limb, they are called efferent reservoir systems Mapleson D, E, F

16. v FGF from machine v FGF from machine Reservoir is in the afferent limb Reservoir is in the efferent limb Efferent limb Afferent limb ARS ERS Patient Patient

17. Enclosed afferent reservoir system Enclosed Mapleson A

18. A D E Humphrey ADE Combined Systems

19. Bidirectional flow Depend on FGF for effective elimination of CO2 Can be manipulated by changing parameters Fresh gas flow Alveolar ventilation Apparatus dead space

20. Fresh gas flow It is imperative to specify optimum FGF for a breathing system for efficient functioning. FGF should be delivered as near the patient’s airway as possible.

21. Fresh gas flow Essential requisite of a breathing system CO2 not eliminated Wastage of gases

22. Apparatus dead space Part of the breathing system from which exhaled alveolar gases are rebreathed without any significant change in their CO2 concentration Volume of the breathing system from the patient end to the point upto which to and fro movement of expired gas takes place.

23. A fferent reservoir system E fferent reservoir system Circle system FGF Expiratory valve

24. Apparatus dead space Should be minimal - rebreathing of CO2 could result in hypercapnia The dynamic dead space depends on FGF and alveolar ventilation The dead space is minimal with optimal FGF If the FGF is reduced below the optimal level , the dead space increases and T he whole system will act as dead space if there is no FGF

25. Afferent reservoir systems Efficient during spontaneous breathing provided the expiratory valve is separated from the reservoir bag and FGF by at least one tidal volume of the patient and apparatus dead space is minimal one tidal volume

26. MAPLESON A MAGILL’S SYSTEM 1921

27. MAPLESON B

28. MAPLESON C

29. v MAPLESON A MAGILL’S CIRCUIT MAPLESON B MAPLESON C AFFERENT RESERVOIR SYSTEMS Patient Fresh gas flow Fresh gas flow Expiratory valve MAPLESON C

30. Lack circuit Lack system has an afferent limb reservoir and an efferent limb through which the expired gas traverses before being vented into the atmosphere . This limb is coaxially placed inside the afferent limb. Efferent limb Afferent limb

31. Mapleson ’s analysis Gases move enbloc . They maintain their identity as fresh gas, dead space gas and alveolar gas- No mixing of gases. The reservoir bag continues to fill up, without offering any resistance till it is full The expiratory valve opens as soon as the reservoir bag is full and the pressure inside the system goes above atmospheric pressure. The valve remains open throughout the expiratory phase without offering any resistance to gas flow and closes at the start of the next inspiration.

32. Functional analysis Mapleson ‘A’/Magill’s system: Spontaneous breathing: system is filled with FG before connecting to the pt. When the pt inspires, FG from the machine and the reservoir bag flows to the pt- bag collapses . During exprn , the FG continues to flow into the system and fill the reservoir bag. The expired gas, initial part - dead space gas, pushes the FG from the corrugated tube into the reservoir bag and collects inside the corrugated tube. As soon as the reservoir bag is full, the expiratory valve opens and the alveolar gas is vented into the atmosphere . During the expiratory pause, alveolar gas that had come into the corrugated tube is also pushed out through the valve, depending on the FGF. The system is filled with only FG and dead space gas at the start of the next insprn when FGF = alveolar ventilation . The entire alveolar gas and dead space gas is vented through the valve and some FG also escapes, if the FGF > MV. Some amt of alveolar gas will remain in the system and lead to rebreathing with a FGF< MV. Max efficiency, when the FGF = alveolar ventilation and the dead space gas has is allowed to be rebreathed and utilized for alveolar ventilation.

33. Controlled ventilation: For IPPV the expiratory valve - partly closed. During insprn , the pt gets ventilated with FG and part of the FG is vented through the valve after sufficient pressure has developed to open the valve. During exprn , the FG from the machine flows into the reservoir bag and all the expired gas flows back into the corrugated tube till the system is full . During next insprn the alveolar gas is pushed back into the alveoli followed by the FG. When sufficient pressure is developed, part of the expired gas and part of the FG escape through the valve. Considerable rebreathing , excessive waste of FG.

34. To summarize afferent reservoir systems..... Mapleson A is efficient only for spontaneous respiration and is inefficient for controlled ventilation Mapleson B and C are inefficient for both spontaneous respiration and controlled ventilation

35. Efferent reservoir systems Works efficiently and economically for controlled ventilation as long as the FG entry and the expiratory valve are separated by a volume equivalent to atleast one TV of the patient Not economical during spontaneous breathing

36. MAPLESON E NO RESERVOIR BAG

37. MAPLESON F

38. Ayre's T-piece (1937) Light metal tube 1 cm in diameter, 5 cm in length with a side arm Used as such, it functions as a non- rebreathing system FGF equal to peak inspiratory flow rate of the patient RESERVOIR TUBE TO PATIENT FRESH GAS FLOW

39. EFFERENT RESERVOIR SYSTEMS MAPLESON D MAPLESON E MAPLESON F Fresh gas from machine Patient Expiratory valve Efferent limb

40. EFFERENT RESERVOIR SYSTEMS BAIN’S CIRCUIT 1972 Bain and Spoerel Patient Afferent limb Efferent limb

41. Machine end Patient end BAIN’S CIRCUIT

42. Bains circuit- spontaneous When pt inspires, the FG from the machine, the reservoir bag and the corrugated tube flow to the pt . During exprn , there is a continuous FGF into the system at the pt end. The expired gas gets continuously mixed with the FG as it flows back into the corrugated tube and the reservoir bag . Once the system is full the excess gas is vented to the atmosphere through the valve situated at the end of the corrugated tube near the reservoir bag. During the expiratory pause the FG continues to flow and fill the proximal portion of the corrugated tube while the mixed gas is vented through the valve . During the next inspiration, the patient breaths FG as well as the mixed gas from the corrugated tube . Many factors influence the composition of the inspired mixture. They are FGF, respiratory rate, expiratory pause, tidal volume and co 2  production in the body. Factors other than FGF cannot be manipulated in a spontaneously breathing patient. FGF should be atleast 1.5 to 2 times the patient’s minute ventilation to minimise rebreathing .

43. Bains -controlled To facilitate IPPV, 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, the corrugated tube and the reservoir bag. During expiration, the expired gas continuously gets mixed with the fresh gas that is flowing into the system at the patient end. During the expiratory pause the FG continues to enter the system and pushes the mixed gas towards the reservoir .When the next inspiration is initiated, the patient gets ventilated with the gas in the corrugated tube i.e., a mixture of FG, alveolar gas and dead space gas . As the pressure in the system increases, the expiratory valve opens and the contents of the reservoir bag are discharged into the atmosphere. Factors that influence the composition of gas mixture in the corrugated tube are FGF, RR, TV and pattern of ventilation. These parameters can be totally controlled by the anaesthesiologist and do not depend on the patient. Using a low respiratory rate with a long expiratory pause and a high tidal volume, most of the FG could be utilized for alveolar ventilation without wastage.   

44. Advantages of Bain’s Light weight Convenient Easily sterilized Scavenging facilitated as the expiratory valve being located away from the patient Exhaled gases in the outer reservoir tubing add warmth to the inspired fresh gases

45. Disadvantages Kinking, leakage and disconnections of inner tube which can cause severe hypercapnia Outer tube should be transparent to allow inspection of the inner tube Special tests

46. Test for Bain’s circuit Set a low flow of oxygen on the flowmeter and occlude the inner tube . The indicator in the flowmeter will fall slightly if the inner tube is intact Pethick test

47. Mapleson A Mapleson B Mapleson C Mapleson D Mapleson E

48. Water’s canister Not used now

49. What is this? Parallel Lack

50. What is this? Parallel Bain

51. Circuit FGF for spontaneous respiration FGF for controlled ventilation Mapleson A 70 – 80 ml/kg/min 2 ½ x MV = 12 – 15 L/min Mapleson B > 2 x MV 20 – 25 L/min 2 – 2.5 x MV Mapleson C 2 – 2.5 x MV 2 – 2.5 x MV Mapleson D 2 x MV or 8 – 10 L/min or 150ml/kg/min 70 ml/kg/min Mapleson E 2 - 3 x MV 2 x MV Mapleson F 2 x MV 1000ml + 100ml/kg

52. Efficiency of Mapleson systems A > DFE > CB DFE > BC > A All Dogs Can Bite Dead Bodies Can’t Argue

53. Conclusion What is a breathing system? What are the components? What are the requisites? What is the classification? Can we identify the different circuits? Functional analysis of each Advantages and disadvantages of each.

54. Thank you