BREATHING SYSTEMS MODERATOR: DR RAJNI MATHURASSO. PROFESSOR,DEPARTMENT OF ANAESTHESIOLOGY,SMS MEDICAL COLLEGE,JAIPUR Presented by: DR. KAUSHLESH SHARMA
DEFINITION• A 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.
It primarily consists of• a) A fresh gas entry port/delivery tube through which gases are delivered from machine to the systems;• b) A port to connect it to patient’s airway;• C) A reservoir for gas ,in the form of bag or a corrugated tubing to meet the peek inspiratory flow requirements;• d) An expiratory port/valve through which the expired gas is vented to the atmosphere.• e) A carbon dioxide absorber if total rebreathing is to be allowed and• f) Corrugated tubes for connecting these components .F low directing valves may or may not be used.
REQUIREMENTS OF A BREATHING SYSTEMEssential:• 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 ; and• d) Have low resistance.
DesirableThe desirable requirements are :-• a) Economy of fresh gas.• b)Conservation of heat• c) Adequate humidification of inspired gas• d) Light weight& convenient during use• E)Efficiency during spontaneous and controlled ventilation• f) Adaptability for adults , children and mechanical ventilators• g) Provision to reduce theatre pollution.
ClassificationOPEN NO BOUNDRY AND NO OXYGEN TUBING NEAR DEAD SPACE PATIENTSEMI OPEN PARTIAL BOUNDRY SCHIMMELBUCH MASK BETWEEN AIRWAY AND ATMOSPHERESEMI closed FULLY BOUNDED .Prevents MAPLESON SYTEM entry of atmsph. Air but vents excess fresh gasClosed No Venting Of Excess Gas Circle system at low flows
Many Configurations NO SODA LIME SODA LIMEUnidirect Non Breathing circle system Circle SystemionalBidirecti a) Afferent reservoir systems. Waters Canisteronal Mapleson A , B ,& C b) Enclosed afferent reservoir systems Miller’s c) Efferent reservoir systems Mapleson D , E & F Bain ‘s system d) Combined Systems Humphery ADE
Components of a Breathing System• Adjustable Pressure Limiting Valve• Reservoir Bag• Tubing
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.
Mechanism of Action• One way , adjustable , spring loaded valve• Valve allows gases to escape when pressure in the breathing system exceeds the valves 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.
Connector and adaptor• A connector is a fitting device intended to join together two or more similar components .• An Adaptor is a specialized connector that establishes functional continuity between otherwise disparate or incompatible components.They can be used to:-• 1. Extend the distance b/w patient & breathing system esp. in head and neck surgeries.• 2. Change the angle of connection b/w patient and breathing system.• 3. Allow a More Flexible and Less kink able connection b/w patient and breathing system .• 4. They increase the Dead space.
RESERVOIR BAG• Also known as Respiratory ,Breathing or sometimes called Rebreathing bag. Standard size is 2l(range from 0.5 to 6l) .• Made up of Rubber and Plastic ,ellipsoid in shape. It has following functions .:-• 1. It allows gas to accumulate during exhalation & provides gas for next inspiration and permits rebreathing.• 2. It provides a means whereby ventilation may be assisted or controlled.• 3. It can serve through visual and tactile observation as a monitor of spontaneous respiration .4. It protects patient from excessive pressure in breathing system.
Tubing• Corrugated or smooth• Different lengths depending on system being used• Allow humidification of inspired air• Parallel and coaxial arrangements available
Mapleson A• Corrugated rubber or plastic tubing: 110-130 cm in length• Reservoir Bag at Machine end• APL valve at the patient end.• Tube volume > Tidal volume
Mapleson A : Functional Analysis• Spontaneous breathing: The system is filled fresh gas before connecting to the patient . When the patient inspires, the fresh gas from the machine and the reservoir bag flows to the patient , and as a result the reservoir bag collapses.
• 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 of the reservoir ,filling it with fresh gas for the next inspiration.
Controlled Ventilation:• To facilitate IPPV the expiratory valve has to be partly closed.• During inspiration the patients gets ventilated with FG and part of the FG is vented through the valve after sufficient pressure has developed to open the valve.
• During expiration , the 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. When sufficient pressure is developed, part of the expired gas and part of the FG escape through the valve.• This leads to considerable rebreathing as well as excessive wastage of fresh gas . Hence these system are inefficient for controlled ventilation.
Mapleson A – Lack Modification• Coaxial modification of Magill Mapleson A.• 1.5 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.• Better for spontaneous ventilation.
• This system functions like Mapleson A both during spontaneous & controlled ventilation.• The only difference is that expired gas instead of getting vented through the valve near the patient ,is carried by an afferent tube placed coaxially and vented through the valve placed near the machine end. This facilitates easy scavenging of expired gases.
Function of Lack modification
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,and 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.
Mapleson C system• This circuit is also known as Water’s circuit.• It is similar in construction to the Mapleson B , but the main tube is shorter.• A FGF equal to twice the to twice the minute ventilation is required to prevent rebreathing. Carbondioxide 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.
Ayre’s T- PIECE• Introduced by Phillips Arye in 1937.• 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
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 patients & pts become light.• 1 inch of expiratory tube can accommodate 2-3 ml of gas.• Gas Flows – 2- 3 times MV
Dis advantages:• High flow rates are required.• Loss of heat & humidity.• Risk of accidental occlusion of expiratory limb- risk of increased airway pressure & barotrauma to lungs.
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 vent• During the controlled ventilation there is little chance of rebreathing.• The FGF which enters during expiratory pause accumulates in the patient end is forced during the inflation.
• In spontaneous breathing during inspiration the patient will inhale the fresh gas & gas in 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 which seems uneconomical is required.• In some cases 250 ml/kg/minrequired to prevent rebreqthing.
Bain circuit• Introduced by Bain & 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• It functions like T-piece except that tube supplying FG to the patient is located inside the reservoir tube.
Specifications:-• Length-1.8 meters.• Diameter of tube-22mm(transparent,carries expiratory gases)• Diameter of inner tubing-7 mm(inspiratory)• Resistance-Less than0.7 cmH2O• Dead space-Outer tube upto expiratory valve( around 500ml=TV)• Flow rates-100-150 ml/kg/min for controlled ventilation. Average 300 ml/kg/min for spontaneous ventilation
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.• During the expiration there is a continuous FGF into the system at the patients end .The expired gas gets continuously mixed with the FG as it flows back into corrugated tubing 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 mix gas is vented through valve.• During the next inspiration , the patient breathes FG as well as mixed gas from the corrugated tube.• It is calculated and clinically prove that FGF should at least 1.5- 2 times the patient’s MV
• 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.• During expiration expired gas continuously gets mixed with FG 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 towards the reservoir.• When 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,APL valve open and the contents of reservoir bag are discharged into the atmosphere.
BAIN CIRCUIT AND IT’ FUNCTION
Mapleson E and F• Valveless breathing system used for children upto 30 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 & 3rd to reservoir tube.
Mapleson E AND F
Maoleson F• The most commonly used T –piece system is the Jackson-Rees’ modification of Ayre’s T- piece (sometimes known as the Mapleson F).• This system connects a two ended bag to the expiratory limb of the circuit;gas escapes via the tail of the bag.
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.• 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.The bag is however not essential to the functioning of the circuit.• IPPV may be performed by occluding the tail of the bag b/w a finger and a thumb and squeezing bag.• Alternatively , a ‘bag-tail valve’,which employs an adjustable resistance to gas flow, may be attached to the bag tail. This causes the bag to remain partially inflated and so facilitates one handed performance of IPPV.• Another aid to IPPV is Kuhn bag which has gas outlet on side of bag.• To prevent rebreathing , system requires a minimal flow of 4 litre/minute,with a FGF of 2.5 to 3 times the patient MV.
Advantages:• Compact,lightweight,no drag to ETT.• Inexpensive,easy to use and sterlize.• No valves.• Minimal dead space• Minimal resistance to breathing• Economical for controlled ventilation• Dis advantages:- kuhn bag• The bag may get twisted and impede breathing.• High gas flow requirement.• Lack of humidification• USES:• Children under 20 kg weight.