The basic anaesthesia machine

know your machine

1. THE BASIC ANAESTHESIA MACHINE Moderated by- Dr.Dipika Choudhury Prof. & Head Presented by- Dr.Hrishikesh Bharali, PGT Deptt . of Anaesthesiology and Critical Care, GMCH

2. ANAESTHESIA MACHINE Anaesthesia machine is a device which delivers precisely known but variable gas mixture, including anaesthetizing and life sustaining gases. Standard guidelines have been given to manufacturers for minimum performance, design, characteristics and safety requirements of machine. The current standard for anesthesia workstation as promulgated by American society for testing and materials (ASTM ) is F1850 . European standard is EN740

3. 3 Types of anesthesia machine Intermittent -Gas flows only during inspiration E.g : Entonox apparatus Continuous -Gas flows both during inspiration and expiration. E.g : Boyle Machine, Forregar Dragger

4. History The original concept of Boyle's machine was invented by the British anaesthetist H.E.G. Boyle in 1917 1920 – A vapourizing bottle isincorporated to the machine . 1930 – Circle absorption system was introduced by Brian Sword 1933 – A dry-bobbin type of flowmeter is introduced. 1937 – Rotameters replaced dry-bobbin type of flowmeters 1952-Pin index safety system (PISS) by Woodbridge

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6. . System components Electrical Pneumatic 1.Master Switch 2.Power Failure Indicator 3.Reserve Power 4.Electrical Outlet 5.Circuit Breakers 6.Data Communication Port 1.High Pressure System 2.Intermediate System 3.Low Pressure System

7. Electrical Components Master Switch Master (main power) switch activates both the pneumatic and electrical functions . Standby position - allows the system to be powered up quickly Computer-driven machines should be turned OFF and restarted with a full checkout at least every 24 hours. STANDBY mode is not used for an extended period.

8. Power failure indicator: Visual or Audible indicator to alert provider of power failure.

9. Reserve Power Backup source of power for the occasional outage is necessary. The anesthesia provider should check the battery status during the preuse checkout procedure. While some older anesthesia machines used replaceable batteries, most new machines use rechargeable batteries. It usually takes a number of hours to fully recharge a battery after it has completely discharged .

10. Electrical Outlets Most modern anesthesia machines have electrical outlets. These are intended to power monitors and other devices. As a general rule, these outlets should only be used for anesthesia monitors. Other appliances should be connected directly to mains power. Fig: Next to each outlet is a circuit breaker .

11. Circuit Breakers There are circuit breakers for both the anesthesia machine and the outlets . When a circuit breaker is activated, the electrical load should be reduced and the circuit breaker reset Data Communication Ports Most modern anesthesia machines have data communications ports. These are used to communicate between the anesthesia machine, monitors, and the data management system

12. Components of pressure systems

13. Pressure units to remember 100 kPa = 1000 mbar = 760 mm Hg = 1030 cm H2O = 14.7 psi = 1 atm 1 psi = 6.8 kpa Psig = pounds per square inch gauge

14. BRIEF NOTE ON CYLINDERS Components: Body Valve – Port, stem Handle Pressure relief device Conical depression Pin index safety system

15. Body: Most medical gas cylinders are made of steel with various alloys added Molybdenum (0.15-0.25%) Chromium (If +  0.8-1.1%) used to increase strength and to minimise weight and wall thickness MRI compatible cylinders are made of aluminium

16. Walls of the cylinder vary from 5/64 to ¼ inch thickness on an average Cylinders that have a marking 3AA are made from steel. The marking 3AL or 3ALM indicates that the cylinder is made from aluminium Cylinder have a flat or a concave base. The other end may taper into a neck that is fitted with tapered screw threads that attach to the cylinder valve

17. Cylinder valves are of 2 types –packed type and diaphragm type Packed type : Capable of withstanding high pressures A.k.a direct acting valve Stem is sealed by resilient packing such as TEFLON which prevents leaks around the threads It is opened by 2-3 turns Used in most of the cylinders

18. Diaphragm valve This valve uses a two piece stem separated by non-perforated diaphragms. These diaphragms prevent leakage along the valve stem. The lower part of the stem is encased in a spring, which forces the stem away from the seat when the valve is opened. The upper stem is threaded into the diaphragm retainer nut. When the handwheel is rotated to the closed position, the upper stem pushes on the diaphragms, which deflect downward, forcing the lower stem against the valve seat. Can be opened fully by ½ to ¾ turns Generally preferred when pressures are relatively low and no leaks can be allowed

19. Port: It is the point of exit for the gas It fits into the nipple on the hanger yoke of the anesthesia machine When installing a cylinder on anesthesia machine, it is important for the user not to mistake the port for the conical depression Stem : Closes the valve by sealing against the seat. When the valve is opened, the stem moves upward,allowing the gas to flow to the port

20. Conical depression Conical depression is situated on the opposite side of the port on the cylinder valve and is situated above the safety relief device It is present on those cylinders which are designed to fit on anesthesia machine Conical depression is designed to receive the retaining screw on the yoke of the anesthesia machine  Screwing the retaining screw into the port may damage the port

21. Pressure Relief Devices: Every cylinder is fitted with pressure relief devices whose purpose is to vent the cylinder’s contents to the atmosphere  if the pressure of enclosed gas increases to dangerous levels Types: Rupture Disc Fusible Plug Combination of Both Pressure Relief valve (spring loaded)

22. Rupture Disc: When pre-determined pressure is reached the disc ruptures and allows the gas contents to be discharged It is a non- reclosing device held against an orifice It protects against excess pressure as a result of high temperature/overfilling

23. Fusible Plug: It is thermally operated It is a non-reclosing pressure relief device where the plug is held against the discharge channel It provides protection against excess pressure due to high temperature but not overfilling Woods metal alloy is most commonly used YIELD TEMPERATURE: Temperature at which fusible material becomes sufficiently soft to extrude from its holder- so that cylinder contents are discharged

24. Spring loaded pressure relief device: It is a reclosing device When set pressure is exceeded, the pressure in the cylinder forced the spring to open the channel for letting out the gases

25. Handle/ Handwheel : It is used to open or close a cylinder valve It is turned counter-clockwise to open and clock-wise to close  this causes the stem to turn A good practice is to attach a handle to each anesthesia machine or other apparatus for which it may be needed

26. Color coding GAS SHOULDER BODY OXYGEN WHITE BLACK NITROUS OXIDE BLUE BLUE CYCLOPROPANE ORANGE ORANGE CARBON DI OXIDE GREY GREY AIR WHITE GREY NITROGEN BLACK BLACK ENTONOX WHITE BLUE

27. Pin Index Safety System It consists of holes on the cylinder valve positioned in an arc below the outlet port A series of pins on the hanger yoke is made to fit into the corresponding indentations The seven hole positions are on the circumference of a circle of 9/16 inch (14.3mm) radius centered on the port

28. GAS PIN INDEX AIR 1,5 OXYGEN 2,5 NITROUS OXIDE 3,5 NITROGEN 1,4 O2-CO2 (CO2 <7.5%) 2,6 O2-CO2 (CO2 >7.5%) 1,6 ENTONOX 7

29. Contents and Pressure In a cylinder containing a non-liquefied gas Pressure declines as the contents are withdrawn Hence pressure can be used to measure cylinder volume(approximately)

30. In a cylinder containing a liquified gas, the pressure depends on VAPOUR PRESSURE of the liquid and is not an indication of the amount of gas remaining in the cylinder as long as the contents are partly in the liquid state Pressure remains nearly constant till all liquid has evaporated After which pressure declines till cylinder is exhausted

31. Consists of: Hanger Yolk Check valve Cylinder Pressure Indicator (Gauge) Pressure Reducing Device (Regulator) Usually not used, unless pipeline gas supply is off

32. Hanger Yoke Assembly . 1) Orients and supports the cylinder 2) Provides a gas-tight seal 3) Ensures uni -directional gas flow The workstation standard recommends that there be at least one yoke each for oxygen and nitrous oxide. If the machine is likely to be used in locations that do not have piped gases, it is advisable to have a double yoke, especially for oxygen.

33. . BODY: Threaded into frame of machine Supports cylinder Hinged Swinging gate RETAINING SCREW: Threaded into the distal end of yoke Tightening the screw – gas tight seal Conical point fits into conical depression on cylinder NIPPLE: Projects from yoke and fits into cylinder port Entrance of gas into machine

34. . INDEX PINS Component of pin index safety system 4mm in diameter and 6mm long (except pin 7 which is slightly thicker) . Fit into the corresponding holes on the cylinder

35. . Bodok seal -cylinders are fitted with yoke with a sealing washer called BODOK SEAL -it is made up of non combustible material and has a metal periphery which make it long lasting. -it should be less than 2.4mm thick prior to compression. -only one seal should be use between the valve & yoke Filter It is used to prevent particulate matter from entering the machine. It is to be placed between the cylinder and the pressure reducing device.

36. Bourdon Pressure gauge Displays cylinder pressure for each gas The gauge is usually colour coded and name and symbol of gas are written over the dial. Blue colour for nitrous oxide and white for oxygen. The scale must be at least 33% greater than the maximum filling pressure of the cylinders or the full indication position. Gauge is calibrated in (kilopascal) kPa or (pound per square inch)psi or Kg/cm 2 . 40

37. Check valve assembly It allows gas from a cylinder to enter the machine but prevents gas from exiting the machine when there is no cylinder in the yoke. Prevents transfer of gas from one cylinder to the other with a lower pressure in a double yoke. It consists of a plunger that slides away from the side of the greater pressure. It is not designed to act as a permanent seal for empty yoke and may allow small amount of gas to escape. As soon as a cylinder is exhausted it should be replaced by a full one or a dummy plug.

38. Pressure reducing device The pressure in a cylinder varies. The anesthesia machine is fitted with devices (reducing valves, regulators, reducing regulators, reduction valves, regulator valves) to maintain constant flow with changing supply pressure. These reduce the high and variable pressure found in a cylinder to a lower ( 40 to 48 psig, 272 to 336 kPa ) and more constant pressure suitable for use in an anesthesia machine. The machine standard requires reducing devices for each gas supplied to the machine from cylinders.

39. BASIC PRINCIPLE A larger pressure acting over a small area is balanced by a smaller pressure acting over a large area . A1 x P1=A2 x P2

40. SIMPLE PRESSURE REGULATOR Adj. screw Spring diaphragm Low pr chamber Valve seating

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42. 46 Safety features on pressure regulator Pressure regulators have safety relief valves If due to any reason there is build up of pressure in pressure regulator then the safety valve blow off at a set pressure of 525 k pa(70psi)

43. INTERMEDIATE   PRESSURE   SYSTEM Begins at the regulated cylinder supply source at 45 psig includes the pipeline sources at 50 to 55 psig and extends to the flow control valve .

44. INTERMEDIATE PRESSURE SYSTEM COMPONENTS Pipeline inlet connections Pipeline pressure indicators Piping Gas power outlet Oxygen pressure failure devices Oxygen flush Additional pressure regulators Flow control valves

45. Pipeline Inlet Connections It is the entry point for gases from the pipelines. The anesthesia workstation standard requires pipeline inlet connections for oxygen and nitrous oxide.Most machines also have an inlet connector for air. These inlets are fitted with threaded non interchangeable Diameter Index Safety System (DISS) fittings A unidirectional (check) valve prevents reversed gas flow from the machine into the piping system Each pipeline inlet is required to have a filter with a pore size of 100μm or less. The filter may become clogged, resulting in a reduction in gas flow.

46. Pipeline Pressure Indicators Indicators to monitor the pipeline pressure of each gas are required by the anesthesia workstation standard. They are usually found on a panel on the front of the machine and may be color coded The workstation standard requires that the indicator be on the pipeline side of the check valve in the pipeline inlet. If the indicator is on the pipeline side of the check valve, it will monitor pipeline pressure only. If the hose is disconnected or improperly connected, it will read “0” even if a cylinder valve is open If a cylinder valve is open and the pipeline supply fails, there will be no change in the pressure on the indicator until the cylinder is nearly empty. Pipeline pressure indicators should always be checked before the machine is used. The pressure should be between 50 and 55 psig (345 and 380 kPa ). The indicators should be scanned repeatedly during use.

47. . Piping is used to connect components inside the machine It must be able to withstand four times the intended service pressure Leaks between the pipeline inlet or cylinder pressure reducing system and the flow control valve not exceed 25 mL /minute Piping

48. Gas Power Outlet One or more gas power (auxiliary gas) outlets may be present on an anesthesia machine. It may serve as the source of driving gas for the anesthesia ventilator or to supply gas for a jet ventilator. Either oxygen or air may be used. The ventilator is an integral part of the modern machine and the breathing system and is connected to the ventilator with internal piping. Therefore, the power outlet is not found in many anesthesia machines today.

49. Oxygen Pressure Failure devic es- These includes- 1.Oxygen Failure safety devices- (Oxygen Failure safety valve,low pressure guardian system, Oxygen Failure protection devices, pressure sensor shutoff system,fail safe,nitrous oxide shutoff valve) This valve shuts off or proportionally decreases and ultimately interrupts the supply of nitrous oxide if the oxygen supply pressure decreases. The anaesthesia workstation standard requires that whenever the oxygen supply pressure reduced below the manufacturer-specified minimum,the delivered oxygen concentration shall not decrease below 19% at the common gas outlet.

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51. Oxygen Flush The oxygen flush (oxygen bypass, emergency oxygen bypass ) receives oxygen from the pipeline inlet or cylinder pressure regulator and directs a high unmetered flow directly to the common gas outlet. It is commonly labeled “02+.” On most anesthesia machines, the oxygen flush can be activated regardless of whether the master switch is turned ON or OFF. A flow between 35 and 75 L/minute must be delivered. The button is commonly recessed or placed in a collar to prevent accidental activation.

52. . OXYGEN FLUSH It consists of a button and stem connected to a spring loaded ball .The ball is in contact with the seat .When the button is depressed, the ball is forced away from the seat , allowing the oxygen to flow to the outlet. A spring opposing the ball will close the valve when the button is not depressed . Hazards : May cause barotrauma Dilution of inhaled anaesthetic Accidental activation Flush may stick and obstruct flow of gases from flowmeter

53. Second-stage Pressure Regulator Some machines have pressure regulators in the intermediate pressure system just upstream of the flow indicators Reduce the pressure further to around 26 psi (177 kPa ) for nitrous oxide and 14 psi (95 kPa ) for oxygen The purpose of this pressure regulator is to eliminate fluctuations in pressure supplied to the flow indicators By reducing the pressures below the normal fluctuation range, the flow will remain more constant. Not all anesthesia machines are equipped with this device.

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56. Contd. It is advantageous to have stops for the OFF and MAXIMUM flow positions. A stop for the OFF position avoids damage to the valve seat. A stop for the MAXIMUM flow position prevents the stem from becoming disengaged from the body . Control Knob : The control knob is joined to the stem. If it is a rotary style knob, the oxygen flow control knob must have a fluted profile and be as large as or larger than that for any other gas. All other flow control knobs must be round. The knob is turned counterclockwise to increase flow. If other types of flow control valves are present, the oxygen control must look and feel different from the other controls.

57. Contd….. When a machine is not being used, the gas source (cylinder or pipeline) should be closed or disconnected. The flow control valves should be opened until the gas pressure is reduced to zero and then closed. If the gas source is not disconnected, the flow control valve should be turned OFF to avoid the fresh gas desiccating the carbon dioxide absorbent and to conserve gas. Before machine use is resumed, the control valves should be checked to make certain that they are closed .

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65. Flowmeter arrangement :- O2 always downstream to all

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69. 76 Link-25 .

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74. References: Understanding anesthesia equipment 5 th edition; Jerry A Dorsch Miller`s Anesthesia 7 th edition Gurudatt C. The basic anaesthesia machine. Indian J Anaesth . 2013;57(5):438-445. doi:10.4103/0019-5049.120138.

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