Breathing Circuits.pptx

Breathing circuits

1. Introductory Class BREATHING CIRCUITS Moderator: Dr. Sanjay Jaswal (Faculty) Dr. Ananya (SR) Presented by: Dr. Abdur Rahaman (JR)

2. FIRST RECOLLECT ABOUT TV, VC, RV

3. WHAT’S ABOUT DEADSPACE ?

4. DEFINE BREATHING SYSTEM Breathing system is defined as an assembly of components which connects the patients airway to the anaesthetic machine creating an artificial atmosphere ,from and into which the patient breathes.

5. REQUIREMENTS OF A BREATHING CIRCUIT Essential Deliver the gases from the machine to the alveoli in the same concentration as set Shortest possible time . Effectively eliminate carbon dioxide. Have minimal apparatus dead space. Have low resistance . Desirable Economy of fresh gas. Conservation of heat Adequate humidification of inspired gas Light weight & convenient during use Efficiency during spontaneous and controlled ventilation Adaptability for adults , children and mechanical ventilators Provision to reduce theatre pollution.

6. It primarily consists of A fresh gas entry A port to connect it to patient’s airway A reservoir for gas ,in the form of bag or a corrugated tubing An expiratory port/valve A carbon dioxide absorber if total rebreathing is to be allowed Corrugated tubes for connecting these components.

7. Adjustable Pressure Limiting Valve Spill valve, pop – off valve, expiratory valve. Designed to vent gas during Positive Pressure. Pressure of less than 0.1 kPa activates the valve when open. Components:- 3 Ports Inlet, patient & exhaust port-later can be open to atmosphere or connected to scavenging system Lightweight disc sits on a knife edge seating held in place by a spring TENSION in the spring and therefore the valve’s opening pressure is controlled by the valve dial.

8. Mechanism of Action One way , adjustable , spring loaded valve Valve allows gases to escape when pressure in the breathing system exceeds the valve's pressure . During spontaneous ventilation: the patient generates a positive pressure during expiration , causing the valve to open. During positive pressure ventilation, a controlled leak is produced in the inspiration by adjusting the valve dial ,allowing control of the patient’s airway pressure.

9. Connector and Adaptor A connector is a fitting device. An Adaptor is a specialized connector -Establishes functional continuity between otherwise disparate or incompatible components.

10. RESERVOIR BAG Also known as Rebreathing bag. Standard size is 2L (range from 0.5 to 6L) . Made up of Rubber and Plastic, ellipsoid in shape. Functions :- Allows gas to accumulate during exhalation. Ventilation may be assisted or controlled. Serve as a visual and tactile observation . Protects patient from excessive pressure in breathing system .

11. TUBING Corrugated or smooth Different lengths depending on system being used Allow humidification of inspired air Parallel and coaxial arrangements available

12. Mapleson A Corrugated rubber or plastic tubing: 110-180 cm in length Reservoir Bag at Machine end APL valve at the patient end. Tube volume > Tidal volume

13. Mapleson A : Functional Analysis Spontaneous breathing The system is filled fresh gas before connecting to the patient During Inspiration : The FG (machine + reservoir bag) flows to the patient. The expired gas , initial part of which is the dead space gas , pushes the FG from the corrugated tube into the reservoir bag and collects inside the corrugated tube. Expiratory pause - Fresh gas washes the expired gas.

14. Mapleson A : Functional Analysis Spontaneous breathing

15. To facilitate IPPV the expiratory valve has to be partly closed. During inspiration: V entilated with FG and part of the FG is vented through the valve. During expiration : FG from the machine flows into the reservoir bag and all the expired gas ( i.e. dead space and alveolar gas) flows back into the corrugated tube till the system is full. During the next inspiration the alveolar gas is pushed back into the alveoli followed by the fresh gas. Part of the expired gas and part of the FG escape through the valve, when sufficient pressure is developed. This leads to considerable rebreathing as well as excessive wastage of fresh gas. Hence these system are inefficient for controlled ventilation. Controlled Ventillation

16. Mapleson A : Functional Analysis Controlled Ventillation

17. Mapleson A – Lack Modification Coaxial modification of Magill Mapleson A & functions like Mapleson A 1.5m in length FGF through outside tube ( 30mm), Exhaled gases from inner tube , vented through the valve placed near the machine end. Inner tube wide in diameter (14 mm) to reduce resistance to expiration(1.6 cm H2O). Reservoir bag & APL valve at machine end. Better for spontaneous ventilation . This facilitates easy scavenging of expired gases.

18. Mapleson A – Lack Modification

19. Mapleson B System The FG inlet is near the patient, distal to the expiratory valve. The expiratory valve open when pressure in the circuit rises. Inhaled mixture of retained fresh gas and alveolar gas. Rebreathing is avoided with fresh gas flow rates of >2MV for both spontaneous and controlled ventilation.

20. Mapleson C system This circuit is also known as Water’s circuit. Similar to Mapleson B , but the main tube is shorter. A FGF equal to 2MV is required to prevent rebreathing . CO ₂ builds up slowly with this circuit. This allows a complete mixing of FG and expired gas. The end result is that these system are not efficient.

21. Mapleson D System It consists of fresh gas inlet nearer the patient end. Expiratory valve and reservoir bag are away from patient end. It is mainly used for assisted or controlled vent. The FGF which enters during expiratory pause accumulates in the patient end and pushes the exp gases towards valve end. In spontaneous breathing during inspiration the patient will inhale the fresh gas from corrugated tube depending on FGF, TV, length of expiratory pause & volume of corrugated tube. Rebreathing can be minimized by increasing FGF 2-3 times the MV . For an adult 15L/min FGF . In some cases 250 ml/kg/min required to prevent rebreathing

22. Bain circuit It is a modification of Mapleson D system and is a co-axial circuit. It functions like T-piece except that tube supplying FG to the patient is located inside the reservoir tube. Most commonly used. And known as Universal circuit . The reservoir bag may be removed and replaced by a ventilator. Has a pressure manometer and PEEP valve. Dead space of the circuit is the volume from the patient end up to the point of separation of the gases. Entire volume of the tubing becomes the dead space If there is a leak in either tubing.

23. Specifications:- Length-1.8 meters. Diameter of Outer tube-22mm ( transparent ,carries expiratory gases) Diameter of Inner tubing-7 mm ( inspiratory ) and GREEN in colour . Resistance-Less than 0.7 cmH2O Dead space- Outer tube upto expiratory valve ( around 500ml=TV) Flow rates- 100-150 ml/kg/min for controlled ventilation. Average 200-300 ml/kg/min for spontaneous ventilation

24. Bain system (Mapleson D) Functional Analysis SPONTANEOUS RESPIRATION Filled with FG First inspires : FG. During expiration : The expired gas gets mixed with the FG. During expiratory pause : FG continues to flow and fill while the mixed gas is vented out through the valve. Second inspiration : Breaths FG as well as the mixed gas. Composition of the inspired mixture : determined by FGF, respiratory rate, tidal volume, end expiratory pause and CO2 production in the body. To minimize rebreathing FGF should be at least 1.5 to 2x MV.

25. CONTROLLED VENTILATION First inspires : FG. During expiration : the expired gas gets mixed . During the expiratory pause : the FG pushes the mixed gas towards the reservoir. Second inspiration ventilated : with mixture of FG, alveolar gas and dead space gas. When the pressure in the system increases, the expiratory valve opens. The degree of rebreathing that occurs depends on the FGF. This system causes less rebreathing that Mapleson B and C . This system functions more efficiently when used for controlled ventilation

26. BAIN CIRCUIT AND IT’S FUNCTION

27. Flow Settings Controlled ventilation : 2 L/min < 10 kg 3.5 L/min = 10–50 kg 70 mL /kg > 60 kg Spontaneous ventilation : 200–300 mL /kg

28. BAIN Circuit ADVANTAGES Can be used for adult and pediatric patient. Spontaneous and controlled ventilation Best Mapleson system for controlled ventilation Light weight. Long length. Coaxial arrangement makes it convenient to use Long length of the circuit. Disposable circuit, however can be easily sterilized and reused Warmth added to the inhaled gases by exhaled gas passing through the outer tubing. DISADVANTAGES Disconnection, kinking or leak of inner tubing. If such, the entire corrugated tubing becomes dead space. This can result in hypercarbia from inadequate gas flow .

29. TEST TO CHECK BAIN CIRCUIT The Pethick test Fill Reservoir Bag Flush high flow oxygen into the circuit. Occlude the patient’s end of the circuit until the. The patient end is then opened and The circuit flushed with oxygen.   Interpretation 1 Bag will deflate -If the inner tube is intact Reason: the venturi effect occurs at the patient end, causing decrease in pressure within the circuit. Interpretation 2 Bag will inflate -If there is a leak in the inner tube. Reason: FG will escape into the expiratory limb and inflate the bag.   BackPressure Test Block the inner tube at the patient end and flush the circuit. No leak in the inner tube. The flow meter bobbins will dip due to the back pressure.

30. Mapleson E and F Valveless breathing system used for children upto 20 kg . Suitable for spontaneous and controlled ventilation. Components:- T shaped tubing with 3 ports. FGF delivered to one port 2 nd port goes to patient & 3 rd to reservoir tube.

31. Ayre’s T- PIECE Belongs to Mapleson E. Available as meatllic / plastic. Length – 2 inches. Parts – inlet, outlet, side tube. Inlet size-10 mm, outlet size-10mm metallic & 15 mm plastic

32. Advantages Simple to use , Light weight. No dead space , no resistance. For pediatric pts. Less than 20 kgs . Expiratory limb is attached to the outlet of T piece. It should accommodate air space equal to 1/3 rd of TV. If too short – air dilution in spont . Breathing & pts become light. 1 inch of expiratory tube can accommodate 2-3 ml of gas. Gas Flows – 2- 3 times MV Disadvantages High flow rates are required. Loss of heat & humidity. Risk of accidental occlusion of expiratory limb- risk of increased airway pressure & barotrauma to lungs.

33. Mapleson F The most commonly used T –piece system is the Jackson-Rees’ modification of Ayre’s . This system connects a two ended bag to the expiratory limb of the circuit. Gas escapes via the tail of the bag.

34. It comprise of- Plastic angle mount Plastic Ayre’s T-piece Corrugated rubber hose. Reservoir bag of 0.5- 1 lit capacity . Green PVC 1.5 meter long tube with plug that fits into the fresh gas outlet of the Boyle’s apparatus. Gas flows required - 2-3 times MV. Dead spce-1 ml/lb( 1KG=2.2LBS) Tidal volume- 3 times dead space .

35. The internal volume of the tube between the patient and the bag should exceed the patient’s tidal volume. FGF flushes expiratory limb during the pause. Expiratory limb should be more than TV to prevent air dilution & rebreathing in spon . Breathing child. This allows respiratory movements to be more easily seen and permits intermittent positive ventilation if necessary. Alternatively , a ‘bag-tail valve’,which employs an adjustable resistance to gas flow, may be attached to the bag tail To prevent rebreathing , system requires a minimal flow of 3 litre /minute , with a FGF of 2 to 3 times the patient MV . CONT…

36. FRESH GAS FLOW Spontaneous ventilation Fresh gas flows of 2–3 x MV to prevent rebreathing , (with a minimum flow of 3 L/min) Mechanical Ventilation Fresh gas flow of 1L + 100 mL /kg/ min to maintain normocapnia . It can be used in adult patients with controlled ventilation using FGF ranging from 70–100 mL /kg/min.

37. Mapleson – F Circuit Advantage Simple Easy to assemble Light weight Portable No valves Least resistance Suitable for pediatric anesthesia , especially head and neck surgery (due to the above factors) Equally effective for both controlled and spontaneous ventilation. Easy to scavenge Inexpensive Disadvantage Wastage of gases—FGF 3 times minute volume Required Lack’s humidification (can be overcome by allowing FG to pass through a humidifier) Occlusion of the relief valve can increase airway pressure producing barotrauma .

38. Suitable for use in Children It is light in weight Low resistance No valve. Suitable for children under 20 kg. It can be used in adult patients with controlled ventilation. FGF ranging from 70–100 ml/kg/min.

39. THE CIRCLE ABSORBER SYSTEM

40. Objectives in a Circle System Maximum reuse of dead space. Maximum reuse of fresh gases. Maximum venting of alveolar gases. FGF should join the inspiratory limb. For paediatric use, low diameter tubes should be used.

41. What are the components? What are the advantages and disadvantages of circle system? How CO2is absorbed ? What are the composition of CO2 absorbents ? What is the chemical reaction taking place during CO2 absorption by SODALIME.

42. COMPONENTS Fresh gas Inlet Unidirectional valves Breathing Tubes Sodalime canister APL valve Reservoir bag (Ventilator Bellows) Patient end.

43. FG Inlet: Position: Downstream to Canister but Upstreram to Inspiratiory valve. Expiratory Pause: FG pushes the expired gas (co2 enriched) -> sodalime -> APL valve. If FGF is high enough, it might be lost via APL too. Disadvantage if FGF Upstream of Sodalime : If FGF enters between patient and exp valve: risk of BAROTRAUMA on activation of O2 flush. Its composition may not immediately reflect inspired gas content. Activation of flush may carry dust. Inhaled anaesthetic is absorbed by sodalime . High flow dry up Sodalime

44. 2. Unidirectional valves: Light disc sitting on a knife- edge seat. Gases normally flow under the seat lifting the disc off the seat and flowing out under the dome. Pressure under the dome firmly seats the disc and prevents retrograde flow. 3. Reservoir Bag Between the expiratory valve and the canister. Reduces the work of expiration, which is the only work of the respiratory muscles under IPPV. If it is located between absorber and inspiratory valve, it reduces the work of inspiration in spontaneous ventilation.

45. 4. APL Valve: Between the expiratory valve and the canister. Allows exhaled gases to escape before passing through sodalime . Downstream the canister will lead to loss of gases. Downstream to the inspiratory valve leads to rebreathing .

46. Ideal Arrangement of Components in a Circle System Unidirectional valve should be placed between the patient and the reservoir valve in each limb. No gases should flow toward the patient via expiratory limb during inspiration. Reservoir bag should not be located between the patient and the expiratory valve. No gases should flow from patient into the inspiratory limb during expiration. APL valve and bag should not be located between the patient and the inspiratory valve. Bag size should be greater than inspiratory capacity (30mL/kg BW). Canister should be atleast twice the tidal volume of the patient ( sodalime contains 50- 70% air around the granules).

47. ADVANTAGES Economical – Gases and inhalational anaesthetic agent Scavenging volume/ load decreases. II. Heat and humidity preservation. III. Low dead space Atmospheric pollution reduced. Arterial CO₂ tension depends on MV, not on FGF DISADVANTAGES Risk of disconnection and misconnection. Slow change in the inspired gas composition particularly with low flow. Dry sodalime / barylime absorbs anaesthetic agent Accumulation of trace gases- CO, H₂, acetone, methane, ethanol. acrylic monomer is exhaled after cementing. Higher FGF would vent this out. Greater resistance to breathing

48. CO2 ABSORBENT

49. Describe the chemical reaction CO₂ + H₂O H₂CO₃ 2NaOH + H₂CO₃ Na₂CO ₃ + 2H₂O Ca(OH)₂ + Na₂CO ₃ CaCO ₃ + 2NaOH

50. Advantages of CO₂ Absorber Neutralization of CO₂ Economical, as low FGF. Less theatre pollution. Hazards of explosion is reduced. Conservation of heat and humidity.

51. Problems with the use of inhalational anaesthetics with CO₂ Absorbant Sodalime + Sevoflurane = Compound A Halothane is degraded to form Halokene . Production of CO (Des > Iso > Halo = Sevo ) Compound A and Halokene are nephrotoxic in rats

52. REFERENCES