Chapter 3 anesthetic_equipment_and_breathing_systems_october_20121
- 1. Anesthetic equipment and Breathing Systems
- 2. Introduction • Delivery of known concentrations of inhaled an esthetics and oxygen to the patient requires ap propriate equipment including an anesthetic m achine, vaporizer, and anesthetic breathing syst em.
- 4. Anesthetic machines • Anesthetic machines, regardless of their manu facturer, consist of the same basic component s. These include:- • A source of compressed gases • Flow meters • Means to vaporize • Anesthetic Breathing Systems
- 5. Common features of anesthesia machine • Inlet of hospital pipeline for compressed gases (oxygen, nitrous oxide, and air) • Inlet of compressed gas cylinders • Pressure regulators to reduce pipeline and cyli nder pressure to safe and consistent levels • Fail-safe device • Flow meters to control the amount of gases de livered to the breathing limb
- 6. Common features of anesthesia machine cont'd.. • Vaporizers for adding volatile anesthetic gas to the carrier gas • Common gas line through which compressed gases mixed with a volatile agent enter the breathing limb
- 7. Breathing limb, including an • Breathing limb, including an – oxygen analyzer, – inspiratory one-way valve, – circle system, – gas sampling line, – spirometer to measure the respiratory rate and volume, – expiratory one-way valve, – adjustable pressure-limiti ng valve, – carbon dioxide absorbent, – reservoir bag, – mechanical ventilator, – scavenging system
- 8. Diagram of the internal circuitry of an anaesthesia machine
- 9. • The anesthetic machine may be equipped with - a mechanical ventilator - devices to monitor the ECG,B/P ,TO & inhale d and exhaled concentrations of oxygen and carbon dioxide. • Alarm systems to signal apnea or disconnection of the anesthetic breathing system from the pati ent are also available.
- 10. 1-Compressed Gases • Gases used in anesthesia are available in cylinders. • Oxygen stored in cylinders in the operating room is a gas • Oxygen and nitrous oxide may be piped to the opera ting room from a central source for delivery to the a nesthetic machine via pressure tubing. • Gas cylinders are attached to yokes on anesthetic m achine. • Color - coded pressure gauges (green for oxygen, blu e for nitrous oxide) on the anesthetic machine indic ate the pressure of the gas in the cylinder.
- 11. 1-Compressed Gases • The pressure in an oxygen cylinder is directly p roportional to the volume of oxygen in the cyli nder. • For example, a full O2cylinder (E size) contains 625 liters of O2at a pressure of 2000 psi and o ne-half this volume when the pressure is 1000 psi.
- 12. 1-Compressed Gases • Therefore, it is possible to calculate accurately h ow long a given flow rate of oxygen can be maint ained before the cylinder is empty. • When gas leaves the cylinder, it enters metal tubi ng in the anesthetic machine and is directed thro ugh a pressure- reducing valve or regulator • some gases support combustion (oxygen, nitrous oxide
- 13. 1-Compressed Gases • Calculation of cylinder contents: The content of th e cylinder is depending on the pressure and the ori ginal volume of the cylinder. For example if the cyli nder normally contain 40 liter and pressurized to 1 20 bar/ atm, the total volume will be (40x 120) =4 800 liter. Therefore, if you constantly uses oxygen 4 liter/min your oxygen will be sufficient for 1200/ min (20 hrs).
- 14. Pressures in the Cylinder & anaesthetic machine • The pressure in the cylinder is 137 Bar; too high for the anesthetic machine. • The pressure is reduced to 4 Bar to protect the mac hine (This pressure would still harm or kill a patient ). • After the rotameters, the pressure is reduced to < 1 /3 Bar to protect the patient. • This requires pressure regulators or pressure releas e valves Pressure regulators and pressure release v alves maintain a constant pressure
- 15. Pressures in the Cylinder... • Different regulators may protect the anestheti c machine (providing 4 Bar) or the patient (by providing <35 kPa, or 1/3 Bar).
- 16. 2-Flowmeter • measures gas flow • Gas flow into the flow meter raises a float that is shaped as a bobbin or ball. • The float comes to rest when gravity is balance d by the fall in pressure caused by the float. • oxygen flows should meet or exceed metabolic requirement • 4-6 lit/min = metabolic requirement
- 17. 2-Flowmeter • The flowmeters are initially calibrated for the i ndicated gas at the factory. • The scale accompanying an O2 flowmeter is gr een and the scale for the nitrous oxide flowme ter is blue.
- 18. 3-Vaporizers Changes liquid agent (halothane, enflurane, isof lurane) to a vapor • To provide a means for anesthetic vapor to be combined with the carrier gas in a controlled manner
- 19. 3-Vaporizers
- 20. 3-Vaporizers Vaporizers classification • Vaporizers are classified as 1. flow - over or 2. bubble - through, depending on the meth od for saturating the carrier gas that flows thr ough the vaporizing chamber.
- 21. 3-Vaporizers • Agent - specific vaporizers are flow- over vapo rizers • The copper kettle and vernitrol are bubble- t hrough vaporizers.
- 22. 3-Vaporizers a. Agent - specific vaporizers • accept the entire fresh gas flow from the anes thetic machine. • Agent - specific vaporizers are temperature- c ompensated by virtue of a heat - sensitive met allic strip. • the vapor concentration is maintained consta nt within certain temperature and flow ranges .
- 24. 3-Vaporizers b. Copper Kettle • A copper kettle receives oxygen as the carrie r gas from a separate dedicated flow meter o n the anesthetic machine. • The efficiency of vaporization is maximized b y passing this carrier gas through a sintered bronze disk at the bottom of the vaporizer (b ubble through) to form streams of fine bubbl es
- 26. 3-Vaporizers • The bubbles produce maximal vaporization eff iciency by providing a large surface for the liqu id-gas interface. • Construction of the copper kettle with copper facilitates the transfer of heat from the surrou nding metal parts of the anesthetic machine a nd environment
- 27. 4- Anesthetic Breathing Systems • Consist of the components necessary to delive r anesthetic gases and oxygen from the anesth etic machine to the patient. • Conceptually, the anesthetic breathing system is a tubular extension of the patient's upper ai rway.
- 28. 4- Anesthetic Breathing Systems • The most commonly used anesthetic breathing syst ems are the Mapleson F (Jackson-Rees system, Bai n circuit, and circle system. • Mapleson breathing system: Mapleson analyzed a nd described five different arrangements of fresh g as inflow tubing, reservoir tubing, facemask, reserv oir bag, and an expiratory valve to administer anest hetic gases.
- 29. 4- Anesthetic Breathing Systems • The five different semi open anesthetic breath ing systems are designated as Mapleson A to E . • The Mapleson F system, which is a Jackson-Re es modification of the Mapleson D system, wa s added later. The Bain circuit is a modification of the Mapleson D system.
- 31. Mapleson breathing system • Flow characteristics of the Mapleson systems ar e characterized by the absence of valves to dire ct gases to or from the patient and the absence of chemical carbon dioxide neutralization. • Because of no clear separation of inspired and e xpired gases, rebreathing occurs when inspirato ry flow exceeds the fresh gas flow.
- 32. Mapleson breathing system • The composition of the inspired mixture depe nds on how much rebreathing takes place. The amount of rebreathing associated with each s ystem is highly dependent on the fresh gas flo w rate. • The optimal fresh gas flow may be difficult to determine.
- 33. Mapleson breathing system • The fresh gas flow should be adjusted when cha nging from spontaneous and controlled ventilati on. Monitoring end-tidal CO2 is the best metho d to determine the optimal fresh gas flow.
- 34. Efficiency of Mapleson • The relative efficiency of different Mapleson s ystems for preventing rebreathing during spon taneous ventilation is A > DF > C > B. • The relative efficiency of different Mapleson s ystems for preventing rebreathing during cont rolled ventilation is DF > B > C > A.
- 35. The Bain circuit • Bain circuit is a coaxial version of the Mapleso n D system in which the fresh gas supply tube runs coaxially inside the corrugated expiratory tubing. • The fresh gas tube enters the circuit near the r eservoir bag, but the fresh gas is actually deliv ered at the patient end of the circuit. • The exhaled gases are vented through the ove rflow valve near the reservoir bag.
- 36. The Bain circuit • The Bain circuit may be used for both spontan eous and controlled ventilation. • Prevention of rebreathing during spontaneous ventilation requires a fresh gas flow of 200 to 300 mL/kg/min and a flow of only 70 mL/kg/ min during controlled ventilation.
- 37. Bain system
- 39. Advantages of the Bain circuit include: • Warming of the fresh gas inflow by the surrounding exhaled gases in the corrugated expiratory tube. • Conservation of moisture as a result of partial rebr eathing • Ease of scavenging waste anesthetic gases from the overflow valve. • It is lightweight, easily sterilized, reusable, and usef ul when access to the patient is limited, such as dur ing head and neck surgery.
- 40. Disadvantages: • Hazards of the Bain circuit include unrecognize d disconnection or kinking of the inner fresh g as tube. • The outer expiratory tube should be transpar ent to allow inspection of the inner tube.
- 41. Anesthetic breathing systems are classified as: Open, Semi open,Semi closed and Closed, accor ding to the presence or absence of: • A gas reservoir bag in the system • Rebreathing of exhaled gases • Means to chemically neutralized exhaled carbon dioxide and • unidirectional valves, • In addition, the composition and flow rate of th e inflow gases should be stated when describing an anesthetic breathing system.
- 42. Classification of anesthetic Breathing systems
- 43. The circle system • It is the most popular anesthetic breathing system in world. • It is so named because its essential components are arranged in a circular manner. • The circle system prevents rebreathing of carbon dioxide by chemical neutralization of carbon dioxi de with carbon dioxide absorbents. • A circle system can be classified as semiopen, sem iclosed, or closed, depending on the amount of fr esh gas inflow.
- 44. The circle system • In a semi open system, very high fresh gas flo w is used to eliminate rebreathing of gases. • A semi closed system is associated with rebrea thing of gases and is the most commonly used breathing system. • In a closed system, the inflow gas exactly matc hes that being consumed by the patient.
- 45. • Rebreathing of exhaled gases in the semi close d and closed circle systems results in: • Some conservation of airway moisture a nd body heat and • Decreased pollution of the surrounding atmosphere with anesthetic gases when the fresh gas inflow rate is set at less tha n the patient's minute ventilation.
- 46. Disadvantages of the circle system include: • Increased resistance to breathing because of the presence of unidirectional valves and carbon dio xide absorbent. • Bulkiness with loss of portability. • Enhanced opportunity for malfunction because of the complexity of the apparatus.
- 47. Impact of rebreathing • Rebreathing of exhaled gases in a semi closed circle sys tem influences the inhaled anesthetic concentrations o f these gases.for example ,when uptake of the anesthet ic gas is high; as during induction of anesthesia, rebreat hing of exhaled gases depleted of anesthetic greatly dil utes the concentration of anesthetic in the fresh gas inf low. • This dilutional effect of uptake is offset clinically by incr easing the delivered concentration of anesthetic. • As uptake of anesthetic diminishes, the impact of diluti on on the inspired concentration produced by rebreathi ng of exhaled gases is lessened.
- 48. Impact of rebreathing • This dilutional effect of uptake is offset clinicall y by increasing the delivered concentration of anesthetic. • As uptake of anesthetic diminishes, the impact of dilution on the inspired concentration prod uced by rebreathing of exhaled gases is lessen ed
- 49. Components of the circle system • A fresh gas inlet • Inspiratory and expiratory unidirectional check val ves • Inspiratory and expiratory corrugated tubing • A Y-piece connector • An adjustable pressure-limiting (APL) valve, also re ferred to as an overflow or “pop-off valve • A reservoir bag • A canister containing carbon dioxide absorbent • A bag/vent selector switch • A mechanical anesthesia ventilator.
- 50. Circle system
- 51. 1-Fresh gas inlet and unidirectional valves: • Fresh gas enters the circle system through a connection fro m the common gas outlet of the anesthesia machine. • Two unidirectional valves are situated in different limbs of the corrugated tubing such that one functions for inhalatio n and the other for exhalation. • These valves • permit positive-pressure breathing and • prevent the rebreathing of exhaled gases until they have passed through the carbon dioxide absorbent canister and ha ve had their oxygen content replenished. •
- 52. • Rebreathing and hypercapnia can occur if the unidi rectional valves stick in the open postion,and total occlusion of the circuit can occur if they are stuck i n the closed positon. • If the expiratory valve is stuck in the closed postion ,breath stacking &barotraumas can occur. • If the unidirectional valves are functioning properl y, the only dead space in the circle system is betwe en the Y-piece and the patient.
- 53. 2-Corrugated Tubing: • The inspiratory and expiratory corrugated tubes se rve as conduits for delivery of gases to and from th e patient. • Their large bore provides minimal resistance, and t he corrugations provide flexibility, resist kinking, a nd promote turbulent instead of laminar flow. • During positive-pressure ventilation, some of the delivered gas distends the corrugated tubing and s ome is compressed within the circuit, which leads to a smaller delivered tidal volume.
- 54. 3.Y-Piece Connector: • A Y-piece connector at the patient end of t he circuit has • A curved elbow, • An outer diameter of 22 mm to fit inside a facemask, and • An inner diameter of 15 mm to fit o nto an endotracheal tube connector.
- 55. 4-Adjustable pressure-limiting valve: • When the “bag/vent” selector switch is set to “bag,” t he APL (overflow or “pop-off”) valve • allows venting of excess gas from the breathing system into the waste gas scavenging system • can be adjusted to allow the anesthetist to provide assi sted or controlled ventilation of the patient's lungs by m anual compression of the gas reservoir bag. • The APL valve should be fully open during spontaneo us ventilation so that circuit pressure remains negligib le throughout inspiration and expiration.
- 56. 5- Reservoir bag: • When the “bag/vent” selector switch is set to “bag, ” the gas reservoir bag maintains an available reser ve volume of gas to satisfy the patient's spontaneo us inspiratory flow rate (up to 60 L/min), which gre atly exceeds conventional fresh gas flows (common ly 3 to 5 L/min) from the anesthesia machine. • The bag also serves as a safety device because its di stensibility limits pressure in the breathing circuit t o less than 60 cm H2O, even when the APL valve is c losed.
- 57. 6-Anesthesia machine ventilators: • When the “bag/vent” selector switch is set to “vent,” t he gas reservoir bag and APL valve are eliminated from the circle anesthetic system and the patient's ventilatio n is delivered from the mechanical anesthesia ventilato r. • Anesthesia ventilators are powered by compressed gas, electricity, or both. • Most conventional anesthesia machine ventilators are pneumatically driven by oxygen or air that is pressurize d and, during the inspiratory phase, routed to the spac e inside the ventilator casing between the compressible bellows and the rigid casing.
- 58. Humidification • Is a form of vaporization in which water vapor (moisture) is added to the gases delivered by t he anesthetic breathing system to minimize w ater and heat loss. • The water formed and the heat generated by c hemical neutralization of carbon dioxide help humidify and heat the gases in the breathing c ircuit.
- 59. Scavenging Systems • Scavenging is the collection and subsequent r emoval of vented gases from the operating ro om. • The excess gas comes from either the APL valv e if the bag/vent selector switch is set to “bag ” or from the ventilator relief valve if the bag/ vent selector switch is set to “vent.” • All excess gas from the patient exits the breath ing system through these valves.
- 60. Scavenging Systems • In addition, when the bag/vent selector switch is set to vent, some anesthetic breathing systems di rect the drive gas inside the bellows canister to th e scavenging system. • The amount of delivered gas used to anesthetize a patient commonly far exceeds the patient's nee ds. • The anesthetist must be certain that the scavengi ng system is operational and adjusted properly to ensure adequate scavenging.
- 61. Closed anesthetic Breathing system(CABS) • In CABS there is total rebreathing of exhaled g ases after absorption of Co2 and the APL valve or relief valve of the ventilator is closed. • A closed system is present when the fresh gas inflow into the circle system (150 to 500 mL/m in satisfies the patient's metabolic o2 require ments (150-250ml/min during anesthesia and replaces anesthetic gases lost by virtue of tissu e uptake.
- 62. Advantages of CABS • Advantages of a closed circle anesthetic breathing sys tem over a semiclosed circle anesthetic breathing sys tem include: 1- Maximal humidification and warming of inhaled gases. 2- Less pollution of the surrounding atmosphere wi th anesthetic gases. 3- economy in the use of anesthetics.
- 63. Danger of CABS • Includes: • Unpredictable and possibly insufficient concent ration of o2 . • Unknown and possibly excessive concentration of potent anesthetic gases.
- 64. Elimination of Carbon dioxide • Chemical neutralization of CO2 is achieved by directing exhaled gases through a container (c anister) containing a carbon dioxide absorbent such as soda lime or bara lyme.
- 66. Composition of CO2 Absorbents Soda Lime Baralyme (Percent of net weight ) (Percent of net weight) • Sodium hydroxide = 4 % Barium hydroxide = 20 % • Potassium hydroxide = 1 % Calcium hydroxide = 80 % • Water = 14-19 % Water = bound water of crystallization in the • Silica = 0.2 % octahydrate salt of barium hydroxide • Calcium hydroxide = 80% Silica = none
- 67. Soda lime • Soda lime granules consist of calcium hydroxide plus smaller amounts of sodium hydroxide and potassium hydroxide that are present as activat ors. • A specific water content of soda lime granules i s necessary to assure optimal activity. • Silica is added to the granules to give hardness and thus minimize the formation of alkaline dus t. • since its inhalation can produce irritation of the airways manifesting as bronchospasm.
- 68. Soda lime • Neutralization of carbon dioxide begins with the reactio n of this gas with the water present in soda lime granul es and exhaled gases to form carbonic acid. • Carbonic acid then reacts with the hydroxides present i n soda lime granules to form carbonates, water, and he at. • The water formed by the neutralization of carbon dioxi de is useful for humidifying the inhaled gases and for di ssipating some of the heat generated in the exothermic neutralization reaction. • The Maximum CO2 absorbed is 23-26lit per 100gm of a bsorbent.
- 69. Soda lime • Accumulation of this highly alkaline of water in the bottom of the canister can produce burns o n contact with the skin. • The heat generated during neutralization of ca rbon dioxide can be detected by warmness of t he canister. • Failure of the canister to become warm to touc h should alert the anesthetist to the possibility that chemical neutralization of carbon dioxide i s not taking place.
- 70. Chemical Neutralization of Carbon dioxide Soda lime……. • CO2 + H2O → H2 CO3 • H2 CO3 + NaOH → Na2 CO3 (rapid) + 2 H2O + H eat • H2 CO3 + Ca (OH)2 → CACO3, (slow) + 2 H2O + H eat
- 71. Baralyme • Baralyme granules consist of barium hydroxide and calcium hydroxide. • Unlike soda lime, the addition of silica to baraly me granules is not necessary to assure hardness . • hardness of baralyme granules reflects the pres ence of bound water of crystallization in the oct ahydrate salt of barium hydroxide. • This bound water also accounts for the more rel iable performance of baralyme than soda lime i n dry environment.
- 72. • Baralyme… • CO2 + H2O → H2CO3 • H2 CO3 + Ba (OH)2 → BaCO3 (rapid) + 2 H2O + Hea t • H2O3 + Ca (OH)2 → CaCO3 (slow) + 2H2O + Heat
- 73. • This checkout, or a reasonable equivalent, should be conducted before administration of anesthesia . • Users are encouraged to modify this guideline to accommodate differences in equipment design a nd variations in local clinical practice. Such local modifications should have appropriate peer review. • Users should refer to the appropriate operator m anuals for specific procedures and precautions.
- 74. • 1. Verify backup ventilation equipment is availabl e and functioning High-Pressure System • *2. Check O2 cylinder supply a. Open O2 cylinder and verify at least half full (about 1000 psig). b. Close cylinder • *3. Check central pipeline supplies; check that ho ses are connected and pipeline gauges read abou t 50 psig
- 75. Low-Pressure System • *4. Check initial status of low-pressure system a. Close flow control valves and turn vaporizers off. b. Check fill level and tighten vaporizers' filler ca ps.
- 76. • 5. Perform leak check of machine low-pressure syst em a. Verify that the machine master switch and flow co ntrol valves are off. b. Attach suction bulb to common (fresh) gas outlet. c. Squeeze bulb repeatedly until fully collapsed. d. Verify bulb stays fully collapsed for at least 10 seco nds. e. Open one vaporizer at a time and repeat steps c an
- 77. 6. Turn on machine master switch and all other ne cessary electrical equipment. 7. Test flowmeters a. Adjust flow of all gases through their full range , checking for smooth operation of floats and undamaged flowtubes. b. Attempt to create a hypoxic O2/N2O mixture and
- 78. Scavenging System • 8. Adjust and check scavenging system a. Ensure proper connections between the scaven ging system and both APL (pop-off) valve and v entilator relief valve. b. Adjust waste-gas vacuum (if possible). c. Fully open APL valve and occlude Y-piece.
- 79. d. With minimum O2 flow, allow scavenger reserv oir bag to collapse completely and verify that ab sorber pressure gauge reads about zero. e. With the O2 flush activated, allow scavenger re servoir bag to distend fully, and then verify that absorber pressure gauge reads < 10 cm H2O.
- 80. Breathing System • 9. Calibrate O2 monitor a. Ensure monitor reads 21% in room air. b. Verify low-O2 alarm is enabled and functioni ng. c. Reinstall sensor in circuit and flush breathing system with O2. d. Verify that monitor now reads greater than 9
- 81. 10. Check initial status breathing system a. Set selector switch to Bag mode. b. Check that breathing circuit is complete, undamaged, and unobstructed. c. Verify that CO2 absorbent is adequate. d. Install breathing-circuit accessory equipmen t (eg, humidifier, PEEP valve) to be used during the cas
- 82. • 11. Perform leak check of the breathing system a. Set all gas flows to zero (or minimum). b. Close APL (pop-off) valve and occlude Y-piece . c. Pressurize breathing system to about 30 cm H 2O with O2 flush. d. Ensure that pressure remains fixed for at least 10
- 83. Manual and Automatic Ventilation Systems • 12. Test ventilation systems and unidirectional valves a. Place a second breathing bag on Y-piece. b. Set appropriate ventilator parameters for n ext patient c. Switch to automatic-ventilation (ventilator) mode.
- 84. e. Set O2 flow to minimum, other gas flows to ze ro. f. Verify that during inspiration bellows deliver a ppropriate tidal volume and that during expira tion bellows fill completely. g. Set fresh gas flow to about 5 L min–1. h. Verify that the ventilator bellows and simulate d lungs fill and empty appropriately without s ustained pressure at end expiration.
- 85. i. Check for proper action of unidirectional valves. j. Exercise breathing circuit accessories to ensure proper function. k. Turn ventilator off and switch to manual ventila tion (bag/APL) mode. l. Ventilate manually and ensure inflation and defl ation of artificial lungs and appropriate feel of s ystem resistance and compliance. m. Remove second breathing bag from Y-piece.
- 86. Monitors 13. Check, calibrate, and/or set alarm limits of all monitors: capnograph, pulse oximeter, O2 anal yzer, respiratory-volume monitor (spirometer), press ure monitor with high and low airway-pressure alarms.
- 87. Final Position 14. Check final status of machine a. Vaporizers off b. APL valve open c. Selector switch to Bag mode d. All flowmeters to zero (or minimum) e. Patient suction level adequate f. Breathing system ready to use