Anaesthesia machine by Dr. shailendra

Basics of anaesthesia machine with safety features

1. ANAESTHESIA MACHINE PRESENTER-DR SHAILENDRA DR RAHUL DR SONAL CO-ORDINATOR-DR GANESH NIKAM SIR

2. The Anaesthesia Machine The anaesthesia machine is a device which delivers a precisely-known but variable gas mixture, including anaesthetizing and life-sustaining gases.

3. BOYLES MACHINE

4. HISTORY The original concept of BOYLE’S MACHINE was invented by the British anaesthetist H.BOYLE in 1917. Prior to this time, anaesthetists often carried all their equipment with them, but the development of heavy, bulky cylinder storage and increasingly elaborate airway equipment meant that this was no longer practical for most circumstances. The anaesthetic machine is usually mounted on anti-static wheels for convenient transportation.

5. HISTORY : • 1917 – Boyle machine with a water sight feed type of flowmeter is introduced by Henry Edmund Gaskin Boyle. • 1920 – A vaporizing bottle is incorporated to the machine. • 1926 – A 2nd vaporizing bottle and by-pass controls are incorporated. • 1930 – A Plunger device is added to the vaporizing bottle. • 1933 – A dry-bobbin type of flowmeter is introduced. • 1937 – Rotameters replaced dry-bobbin type of flowmeters

6. BOYLE ANAESTHESIA MACHINE Modification of original machine developed by Dr. Henry Boyle in 1917 Coxters dry flow meter allowed proportioning of O 2 , CO 2 & N 2 O V aporizing bottles Bottom illustrations: Case with accessories Machine stand with four cylinder yokes (2 each for N 2 O and O 2 ) + carrying handle

7. DEPENDING ON THE PRESSURES WITHIN THE MACHINE 3 CIRCUITS - HIGH PRESSURE INTERMEDIATE PRESSURE LOW PRESSURE

8. The Anesthesia Machine High Low Pressure Circuit

9. HIGH PRESSURE CIRCUIT CYLINDERS CYLINDERS PRIMARY PRESSURE REGULATORS OXYGEN- --2200psi------45psi NITROUS OXIDE---745psi----45psi

10. Intermediate pressure circuit From regulated cylinder supply sources to flow control valves Second stage pressure regulator

11. LOW PRESSURE CIRCUIT FROM FLOW CONTROL VALVES TO COMMON GAS OUTLET INCLUDES - FLOW TUBES VAPORISERS ONE WAY CHECK VALVE

12. High Pressure system It consists of - Hanger yoke Cylinder pressure indicator (gauge) Pressure regulator

13. HPS - Hanger yoke Functions Orients and supports the cylinder Provides a gas tight seal Ensures unidirectional gas flow At least one yoke for O2 and N2O each If no pipeline gas conn then a double yoke is advisable

14. Hanger Yoke

15. HANGER YOKE Parts Body Threaded onto the frame of the machine Provides support for cylinder Swinging gate type yoke Retaining screw Conical point of the retaining screw is received onto the conica l depression on the cylinder valve Enables a gas tight seal Nipple Fits into the port on the cylinder valve

16. HPS - Hanger yoke Parts 4. Index Pins The Pin Index Safety System (PISS) pins are below the nipple The holes into which the pins are fitted must be of specific depth 5. Washer (Bodok’s Seal) Produces a seal between the cylinder valve and the yoke A broken or curled washer must not be used 6. Filter Should be installed between the cylinder and the pressure regulator or the flow control valve Prevents particulate matter from entering the machine

17. HPS - Hanger yoke Parts 7. Check valve Assembly Allows gas to enter the machine but prevents gas from exiting the machine when there is no cylinder in the yoke Prevents gas from being transferred from one cylinder at higher pressure to another one with lower pressure

18. HPS - Hanger yoke Parts 7. Check valve Assembly When cylinder P > machine P the “plunger” in the check valve assembly moves to the right – gas flows into the machine When machine P > Cylinder P the plunger moves to the LEFT – px escape of gas from the machine

19. HPS - Hanger yoke – check valve assembly

20. HPS - Hanger yoke Parts Check valve Assembly May allow a small amount of gas to escape To minimize such losses a ‘yoke plug’ should be used on an empty yoke. YOKE PLUG

21. HPS – Placing a cylinder in the yoke 1. Personnel should wash their hands first 2. Not to contaminate the yoke 3. Check the 2 pin index safety system 4. Retract the retaining screw 5. Open the swinging gate 6. Washer is placed over the nipple 7. Cylinder is then supported with foot and raised into the yoke

22. HPS – Placing a cylinder in the yoke 8. Cylinder valve is guided over the nipple and index pins are engaged in appropriate holes 9. Gate is then closed 10. Retaining screw is tightened 11. Cylinder is opened. Make certain that the cylinder is full and that there is no hissing sound 12. Valve should be kept closed

23. HPS – Placing a cylinder in the yoke

24. Pin Index Safety System (PISS)

25. Pin index safety system

26. HPS –Cylinder pressure indicator/gauge 1. Displays cylinder P for each gas supplied by the cylinder 2. Scale must be at least 33% greater than the maximum filling P of the cylinder E.g. Bourdon Pressure Gauge 3. Calibration in kPa or psi 4. Digital pressure readouts and LED displays also available with some machines

27. HPS –Cylinder pressure indicator 4. Consists of a hollow metal tube bent into a curve then sealed and linked to a clocklike mechanism. The other end is connected to a gas source. 5. Inc in Gas P inside the tube – straightens the tube – motion is transmitted to the indicator – indicator moves along a calibrated scale – P reading obtained

28. HPS –Bourdon Gauge

29. Pressure Reducing Regulator Converts high & variable pressure in the cylinder into a constant working pressure suitable for use in Anaesthesia machine .

30. HPS –Pressure Regulator Working Principles: a) P = force acting against an area b) F = P x A c) Pc Inlet Pressure d) Pr Outlet pressure e) A1 Area of seat occluding C and R f) A2 Area of the flexible diaphragm Pc x A1 = Pr x A2

31. 1

32. HPS –Pressure Regulator Working Principles: a) When the flow meter is opened, Pc x A1 >> Pr x A2 b) The flexible diaphragm becomes flatter and the balance tips to the right c) The seat A1 no longer occludes the opening bet C and R --- gas flows from cylinder into machine .

33. HPS –Pressure Regulator Working Principles: a) This regulator will yield a constant pressure only if Pc is constant. Pc decreases as cylinder pressure falls b) It would hence be needed to constantly adjust the flow meter to compensate for the pressure drop c) To remedy this a main spring S1 is added. S1 is an adjustable screw which exerts a downward force on the flexible diaphragm d) Therefore, (Pc x A1) + FS1 = Pr x A2

34. HPS –Pressure Regulator Working Principles: An additional spring S2 is added to prevent gas from flowing from cylinder to R when the adjustable S1 spring is completely relaxed and the flow meter is open S2 is also called the sealing (shutoff) spring Therefore, (Pc x A1) + (FS1 – FS2) = Pr x A2

35. Advantages Fine adjustment is not necessary to maintain a constant flow. Fine adjustments of low flows are possible. There is less chance of bursting of the tubing & blowing up of connection.

36. Intermediate Pressure ystem The intermediate pressure system receives gases from the pressure regulators or the anesthesia machine Controlled by the master switch When the master switch is turned OFF the pressure in the intermediate system drops to zero 40

37. Intermediate Pressure system System Parts- 1. Master switch (pneumatic component) 2. Pipeline inlet connections 3. Pipeline pressure indicators 4. Piping 5. Gas Power outlet 6. Oxygen Pressure failure devices 7. Gas selector switch 8. Second stage pressure regulator 9. Oxygen Flush 10.Flow adjustment controls

38. 1. Master Switch (pneumatic component) Located downstream of the inlets for the cylinders and pipeline supplies Oxygen flush is independent of this switch INTERMEDIATE PRESSURE

39. Intermediate Pressure system System 2. Pipeline inlet Connections Entry point for gases from the pipeline The inlets are fitted with threaded interchangeable DISS Diameter Index Safety System Fittings Unidirectional check valve to px reversed gas flow from machine to pipeline or atmosphere Filter of pore size 10 microns or less

40. Pipeline inlet Connections

41. Pipeline Gas Supply - DISS Stem and body mate via two shoulders on the stem that match two bores in the inlet Designed for < 200 psi pressures

42. Intermediate Pressure system System 3. Pipeline pressure indicators Usually found on a panel in front of the machine May be colour coded Correct range of pressure maybe indicated by a coloured zone Digital indicators and LED displays also available Pipeline pressure should be between 50-55psig (345-380 kPa)

43. Intermediate Pressure system System 4. Piping Used to connect components inside the machine Must be able to withstand four times the intended service pressure without rupturing Leaks between pipeline inlet/cylinder pressure reducing system and Flow control valve should not exceed 25ml/min If the yoke and pressure regulators are included the leak should not exceed 150ml/min

44. Intermediate Pressure system System 5. Gas Power Outlet One or more auxiliary gas outlets may be present Serve as a source of driving gas for the ventilator or to supply gas for a jet ventilator Nowadays however the ventilator is an integral part of the machine and the power outlet is not found on many anesthesia machines today

45. Intermediate Pressure system System 6. Oxygen Pressure failure devices Oxygen Failure safety device Oxygen supply failure alarm

46. Oxygen Failure safety device oxygen failure safety valve (oxygen failure safety device, low-pressure guardian system, oxygen failure protection device, pressure sensor shutoff system or valve, fail safe, pressure sensor system, nitrous oxide shutoff valve) There are 2 kinds of fail-safe valves Pressure sensor shut-off valve ( Ohmeda ) Oxygen failure protection device ( Dragger )

47. Pressure Sensor Shut-Off Valve The Ohmeda pressure sensor shut-off valve is a threshold valve which is either open or closed. O 2 supply pressure opens the valve as long as it is above a pre-set minimum value (e.g.. 20 psig). If the O 2 supply pressure falls below the threshold value the valve closes and the gas in that limb (e.g.. N 2 O), does not advance to its flow-control valve.

48. Intermediate Pressure system System Oxygen Failure Safety Device Shuts off or proportionately decreases and ultimately interrupts the supply of N2O if the oxygen supply pressure decreases When pneumatic system is activated --- O2 pressure reaches the OFSD – allows other gases to flow Turning OFF the pneumatic system --- O2 in the machine is vented out into the atmosphere --- decrease in the O2 pressure – OFSD interrupts the supply of other gases to their flow control valves

49. Intermediate Pressure system System Oxygen Failure Safety Device Machine standard requires that an anesthesia machine be designed so that whenever the O 2 supply pressure is reduced below normal, the O 2 concentration at the common gas outlet does not fall below 19% When the pressure from the O 2 regulator falls, the slave regulator of the N 2 O will automatically close & will not allow flow of N 2 O.

50. Intermediate Pressure System Oxygen Failure Safety Device O2 pressure normal – plunger and seal assembly are depressed – ax gases can flow thru the valve O2 pressure dec – spring forces the plunger and seal assembly upwards – narrows the valve opening in proportion to O2 supply Pressure loss

51. Intermediate Pressure system System Oxygen Failure Safety Device When O2 supply pressure fails completely – valve closes If the OFSD is working properly then the flow indicator of other gases will fall to the bottom before the O2 indicator falls to the bottom of the tube .

52. (OFPD)

53. Oxygen Supply Failure ALARM Pneumatic alarms Cannot be disabled visual, audible or both When O2 falls < 30 psig (205kPa) {manufacturer specified threshold} – within 5 seconds –alarm is activated – it is not possible to disable this alarm Both OFSD and O2 supply failure alarm depend on Pressure and not on flow Aid in preventing hypoxia caused by problems occurring upstream in the machine circuitry

54. Pneumatic alarms Uses a pressurized canister that is filled with O 2 when the anesthesia machine is turned on. When the O 2 pressure falls below a certain value, the alarm directs a stream of O 2 through a whistle

55. Intermediate Pressure system System Oxygen Failure Devices Disadvantages – Do not prevent anesthetic gases from flowing Equipment problems or operator errors that occur downstream are not prevented Do not guard against accidents from gas crossovers in cylinder or pipeline systems

56. Intermediate Pressure System 7. Gas selector switch Prevents Air and N2O from being used together 8. Second Stage Pressure regulator Some machines have these located just upstream of the flow indicators These receive gas from either the pipeline or the pressure regulator and reduce it further to around 14 psig (95 kPa) for O2 26 psig (177 kPa) for N2O

57. Intermediate Pressure system System 9. Oxygen Flush Directs a high unmetered flow directly to the common gas outlet Commonly labeled as “ O2 +” It is a single purpose self closing device operable with one hand designed to minimize accidental activation Low between 35 – 75 L/min

58. Intermediate Pressure system System 9. Oxygen Flush Consists of a button and stem connected to a ball. The ball is in contact with the seat Button depressed – ball is forced away from the seat – allows oxygen to flow to the outlet A spring opposes the ball which will close the valve when the button is not depressed

59. Intermediate Pressure system m 9. Oxygen Flush May or may not result in other gas flows being shut off Pressure may be transmitted back to indicators and vaporizers – may change the vaporizer output and the flow indicator readings However the standardization requires that the O2+ flush activation does not increase or decrease the pressure at the vaporizer outlet by >10kPa or increase the vapor output by >20%

60. Intermediate Pressure System 9. Oxygen Flush Hazards Accidental activation Internal leakage – O2 enriched mixture is delivered Sticks to the ON position May obstruct the flow of other gases Barotrauma Awareness during anesthesia

61. Intermediate Pressure System 10. Flow Adjustment Control Regulates the flow of O2, air and other gases to the flow indicators 2 types Mechanical Electronic Standard requires that there be only One flow control for each gas

62. Intermediate Pressure System Mechanical Flow control valve Components Body – screws into the anesthesia machine Stem and seal – have fine threads so that the stem moves only a little when a complete turn is made Valve is closed – pin at the end of the stem fits into the seat – occludes the orifice – no gas passes Stem is turned outward – creates an opening bet the pin and the seat – gas flows Greater space between the pin and seat -- greater volume of gas can flow

63. Intermediate Pressure System Mechanical Flow control valve Components Control knob – rotatory style knob, with a fluted profile, round in shape and is of same size or larger as compared to other knobs Turned counterclockwise to increase flow Stops should be there for the OFF and MAXIMUM flow positions. This helps avoid damage.

64. Intermediate Pressure System Mechanical Flow control valve Flow control valve should be kept opened until the gas pressure is reduced to zero after the cylinder/pipeline system is shut off. Should be turned off– avoids fresh gas desiccating the CO2 absorbent and also conserves gas Before machine resumed – check whether flow valves are closed – otherwise sudden rise may damage the apparatus.

65. Intermediate Pressure System Mechanical Flow control valve Problems If loose may respond to light touch or even accidental brushing Should be closed when not in use The stem or seat can block the flow

66. Low pressure system - The low-pressure system is downstream of the flow control devices up to common gas outlet .

67. Low pressure system Flowmeters Hypoxia prevention safety devices, Unidirectional valves, Pressure relief devices, Common gas outlet. Vaporizers

68. Flowmeters ( flow indicators, flow tubes, rotameters ) mechanical Electronic Mechanical Flowmeters measure the drop in pressure that occurs when a gas passes through a resistance .

69. Traditional mechanical flow indicators used in anesthesia machines have been of the variable orifice (variable area, Thorpe tube) type vertical glass tube is internally tapered with its smallest diameter at the bottom. It contains an indicator that is free to move up and down inside the tube

70. Physical principles 1)Pressure drop across the constriction: The loss of energy as gas passes the float is reflected in a pressure drop across the float. This pressure drop is given by: Weight of float cross sectional area 2)Size of annular opening : The larger the annular opening greater the flow of gas

71. Physical principle 3)Physical characteristics of the gas : Low Flow : Small annular space, therefore flow is laminar; therefore flow is a function of gas viscosity ( Poiseuille’s Law) High Flow : Large annular space, therefore flow is turbulent; therefore the flow is a function of gas density (Graham’s Law)

72. Physical principle Temperature and Pressure Effects Flowmeters are calibrated at atmospheric pressure (760 torr ) and room temperature (20°C). Temperature and pressure changes will affect both the viscosity and the density of a gas and so influence the accuracy of the indicated flow rate. Variations in temperature as a rule are slight and do not produce significant change hyperbaric chamber, a flowmeter will deliver less gas than indicated. With decreased barometric pressure (increased altitude), the actual flow rate will be greater than that indicated

73. Flowmeter Assembly tube Indicator stop scale Lights

74. Tube

75. Indicator (float or bobbin )

76. Stop stop at the top of the flowmeter tube prevents the indicator from plugging the outlet, which could lead to damage to the tube prevents the indicator from ascending to a point in the tube where it cannot be seen

77. Stop

78. Scale The anesthesia machine/workstation standard requires that the flow indicator scale either be marked on or immediately adjacent to the tube . Flowmeters are calibrated in liters per minute. For flows below 1 L/minute, the flow may be expressed either in milliliters or in decimal fractions of a liter per minute with a zero before the decimal point . Lights Optional on most modern anesthesia machines. These are useful when the machine is used in a darkened room

79. Flowmeter Tube Arrangement

80. Flowmeter tube sequence

81. Problems with flowmeter 1.Leaks a) Between the glass flow tubes & the metal manifold. b)in cracked or broken glass flow tubes. 2.Inaccuracy Dirt & static electricity can cause the float to stick. Back pressure (ventilator & breathing circuit )can cause a float to drop so that it reads less than the actual. Slanting tube distorts the annular space.

82. LOW PRESSURE PIPING The piping in the machine b/w the flow control valve and the common gas outlet must not exceed 30ml per minute at a pressure of 3 k Pa (30 cm H 2 O) with a vaporizer either in the ON, OFF or, if possible, in the detached position. May be subjected to breakage / leaks.

83. UNIDIRECTIONAL CHECK VALVE When controlled / assisted ventilation is used positive pressure may be generated that may be transmitted back to the machine. Causes: Affect the concentration of volatile Anaesthetic agents from vaporizer. Increase leaks Inaccurate flow indicator reading. To prevent that a unidirectional valve is present b/ w vaporizer & common gas outlet , upstream of where the O 2 flush flow joins the FGF.

84. COMMON GAS OUTLET It receives all the gases & vapors from the machine. Most machines have a 15mm female slip joint connection, with a coaxial 22mm male connection. Fresh gas supply tube, which conveys gas to the fresh gas inlet in the breathing system, attaches to the common gas outlet. Frequent site for a leak/disconnection

85. Hypoxia Prevention Safety Devices Mandatory Minimum Oxygen Flow Minimum Oxygen Ratio Mechanical Linkage Electronic Linkage

86. SAFETY FEATURE

87. USE Safety devices are to prevent delivery of hypoxic mixture. Regulation to prevent excessive pressure which is traumatic to patient

88. HIGH PRESSURE SYSTEM Gas cylinder – Color coding Cylinder labels Symbol of gas Pin index safety system (PISS) Safety relief valve Filling within service pressure

89. Pin indices

90. Safety Relief Device Composed of atleast one of the following – Frangible disc (Bursts under extreme pressure) Fusible Plug (Of wood’s metal which has a low melting point) Safety relief valve (Opens at extreme pressure)

91. Check valves at cylinder inlet and pipeline inlet Cylinder pressure indicator (BOURDON’s pressure gauge) Pressure regulator Pressure relief valves Washer (BODOK seal) – Rubber made of neoprene

92. Safety features in cylinder pressure indicator Gauge usually color coded Name and symbol of gas over dial If bourdon tube ruptures gas is vented from back side Gauges are angled and placed in such a way that it can be easily read Instructions like ‘use no oil’ / ‘open valve slowly’ written on the gauge

93. Safety features of pressure regulator Pressure regulators have safety relief valves Safety valves blow off at a set pressure of 525kpa (70psi )

94. P ipeline Wall outlet- labelled and color coded Primary valve/automatic shut off valve Secondary valve/isolation valve Schrader’s probes , quick connectors or diameter index safety system (DISS) to prevent interchangeability Pipeline hoses – color coded

95. O2 supply pressure failure devices The anesthesia gas supply device shall be designed so that whenever O2 supply pressure is reduced to below the manufacturer specified minimum , the delivered O2 conc shall not decrease below 21% at the common gas outlet .

96. Fail safe valve – Downstream to the NO2 supply source This valve shuts off or proportionally decrease the supply of nitrous oxide ( and other gases ) if the O2 supply pressure declines Operates in threshold manner O2 supply pressure opens the valve and the valve return spring closes the valve

97. O2 failure protection device The pressure of all gases controlled by the OFPD will decrease proportionally with O2 pressure Consists of nozzle assembly connected to a spring loaded piston

98. Flowmeters The O2 flow control knob is distinctively fluted, projects beyond the control knobs of other gases and is larger in diameter Knobs are color coded for appropriate gases Name of gas is marked on each knob If a single gas has 2 flow tubes , the tubes are arranged in series and controlled by a single flow control valve An O2 leak from flow tube can produce a hypoxic mixture regardless of arrangement of flow tubes

99. Flowmeters Bobbin rotates on flow which prevents it from sticking Antistatic spray in flowmeters Master and slave safety mechanism for gas delivery between O2 & NO2 (pressure of O2 ‘master’ flow is required to release the flow of N2O ‘slave’) Downstream placement of O2 flowmeter Float stop Auxillary O2 flowmeter

100. Hypoxia Prevention safety system LINK 25 – Allows independent adjustment of either valve , automatically intercedes to maintain min 25% O2 conc with a maximum n2o-o2 flow ratio 3:1 Increases O2 flow to prevent hypoxic gas delivery 14-tooth sprocket ( N2O flow control valve) 29-tooth sprocket (O2 flow control valve)

101. Mandatory minimum O2 flow – 50 to 250ml/min O2 ratio monitor controller limit N2O flow to prevent delivery of hypoxic gases

102. O2 supply failure alarm When O2 supply pressure falls below manufacturer specified threshold (30psig/205kpa) After the fall of pressure alarm should activate within 5 seconds RICHIE WHISTLE – when O2 pressure falls below 260kpa(38psi) whistle valve opens It sounds continously until O2 pressure has fallen to approx 40.5kpa/6psi At 30 psi it cuts off the supply of anaesthetic gases to patient

103. O2 flush valve Receives O2 from pipeline inlet/pressure regulator & directs a high unmetered flow directly to CGO Activates regardless of master switch 35 to 75 ml/min Button is pressed in collar to prevent accidental activation Activation does not increase the pressure at vaporizer outlet > 10kpa or vapor output by > 20%

104. Check valve Prevent backflow into the vaporizer during positive pressure ventilation , thereby minimizing the effects of intermittent fluctuations in downstream pressure on concentration of inhaled anesthestic

105. Thank you