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Anesthetic machine for student

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The document provides an overview of the key components and systems of an anesthesia machine, including: 1) The high pressure and low pressure systems that deliver gases from cylinders or pipelines to the vaporizers and breathing circuit. 2) Safety features like fail-safe valves that monitor oxygen pressure and proportion gas flows to prevent hypoxic mixtures. 3) Components of the breathing circuit like the adjustable pressure limiting valve and circle system configuration. 4) The scavenging system that protects the circuit from excessive pressures and pollution of the operating room.

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Introductory Lecture Series: The Anesthesia Machine PORNSIRI WANNADILOK
Objectives Anesthesia Machine Ventilators Scavenging Systems System Checkout
vaporizer bellow Corrugated tube Soda lime Flow meter ventilator APL valve Scavenging system
The Anesthesia Machine High Intermediate Low Pressure Circuit
High Pressure System Receives gasses from the high pressure E cylinders attached to the back of the anesthesia machine (2200 psig for O2, 745 psig for N2O) Consists of: Hanger Yolk (reserve gas cylinder holder) Check valve (prevent reverse flow of gas) Cylinder Pressure Indicator (Gauge) Pressure Reducing Device (Regulator) Usually not used, unless pipeline gas supply is off
E Size Compressed Gas Cylinders 1800 838 750 2000 Pressure Full (psig) 8.90 8.80 6.76 Full Weight (kg) 5.90 5.90 5.90 5.90 Empty Weight (kg) 625 1590 1590 625 Contents (L) Gas Liquid and gas Liquid and gas Gas State Black/White (yellow) Gray Blue White (green) Color Air Carbon Dioxide Nitrous Oxide Oxygen Cylinder Characteristics
Hanger Yolk Hanger Yolk: orients and supports the cylinder, providing a gas-tight seal and ensuring a unidirectional gas flow into the machine Index pins: Pin Index Safety System (PISS) is gas specific prevents accidental rearrangement of cylinders (e.g.. switching O2 and N2O)
Pressure Reducing Device Reduces the high and variable pressures found in a cylinder to a lower and more constant pressure found in the anesthesia machine (45 psig) Reducing devices are preset so that the machine uses only gas from the pipeline (wall gas), when the pipeline inlet pressure is 50 psig. This prevents gas use from the cylinder even if the cylinder is left open (i.e. saves the cylinder for backup if the wall gas pipeline fails)
Pressure Reducing Device Cylinders should be kept closed routinely. Otherwise, if the wall gas fails, the machine will automatically switch to the cylinder supply without the anesthetist being aware that the wall supply has failed (until the cylinder is empty too).
Intermediate Pressure System Receives gasses from the regulator or the hospital pipeline at pressures of 40-55 psig Consists of: Pipeline inlet connections Pipeline pressure indicators Piping Gas power outlet Master switch Oxygen pressure failure devices Oxygen flush Additional reducing devices Flow control valves
Pipeline Inlet Connections Mandatory N2O and O2, usually have air and suction too Inlets are non-interchangeable due to specific threading as per the Diameter Index Safety System (DISS) Each inlet must contain a check valve to prevent reverse flow (similar to the cylinder yolk)
Oxygen Pressure Failure Devices Machine standard requires that an anesthesia machine be designed so that whenever the oxygen supply pressure is reduced below normal, the oxygen concentration at the common gas outlet does not fall below 19%
Oxygen Pressure Failure Devices A Fail-Safe valve is present in the gas line supplying each of the flowmeters except O2. This valve is controlled by the O2 supply pressure and shuts off or proportionately decreases the supply pressure of all other gasses as the O2 supply pressure decreases Historically there are 2 kinds of fail-safe valves Pressure sensor shut-off valve (Ohmeda) Oxygen failure protection device (Drager)
Pressure Sensor Shut-Off Valve Oxygen supply pressure opens the valve as long as it is above a pre-set minimum value (e.g.. 20 psig). If the oxygen supply pressure falls below the threshold value the valve closes and the gas in that limb (e.g.. N2O), does not advance to its flow-control valve.
Oxygen Failure Protection Device (OFPD) Based on a proportioning principle rather than a shut-off principle The pressure of all gases controlled by the OFPD will decrease proportionately with the oxygen pressure
Oxygen Supply Failure Alarm The machine standard specifies that whenever the oxygen supply pressure falls below a manufacturer-specified threshold (usually 30 psig) a medium priority alarm shall blow within 5 seconds.
Limitations of Fail-Safe Devices/Alarms Fail-safe valves do not prevent administration of a hypoxic mixture because they depend on pressure and not flow. These devices do not prevent hypoxia from accidents such as pipeline crossovers or a cylinder containing the wrong gas
Limitations of Fail-Safe Devices/Alarms These devices prevent hypoxia from some problems occurring upstream in the machine circuitry (disconnected oxygen hose, low oxygen pressure in the pipeline and depletion of the oxygen cylinder) Equipment problems that occur downstream (for example leaks or partial closure of the oxygen flow control valve) are not prevented by these devices.
Oxygen Flush Valve (O2+) Receives O2 from pipeline inlet or cylinder reducing device and directs high, unmetered flow directly to the common gas outlet (downstream of the vaporizer) Machine standard requires that the flow be between 35 and 75 L/min The ability to provide jet ventilation Hazards May cause barotrauma Dilution of inhaled anesthetic
Second-Stage Reducing Device Located just upstream of the flow control valves Receives gas from the pipeline inlet or the cylinder reducing device and reduces it further to 26 psig for N2O and 14 psig for O2 Purpose is to eliminate fluctuations in pressure supplied to the flow indicators caused by fluctuations in pipeline pressure
Low Pressure System Extends from the flow control valves to the common gas outlet Consists of: Flow meters Vaporizer mounting device Check valve Common gas outlet
Flowmeter assembly When the flow control valve is opened the gas enters at the bottom and flows up the tube elevating the indicator The indicator floats freely at a point where the downward force on it (gravity) equals the upward force caused by gas molecules hitting the bottom of the float
Arrangement of the Flow-Indicator Tubes In the presence of a flowmeter leak (either at the O ring or the glass of the flow tube) a hypoxic mixture is less likely to occur if the O2 flowmeter is downstream of all other flowmeters In A and B a hypoxic mixture can result because a substantial portion of oxygen flow passes through the leak, and all nitrous oxide is directed to the common gas outlet * Note that a leak in the oxygen flowmeter tube can cause a hypoxic mixture, even when oxygen is located in the downstream position
Proportioning Systems Mechanical integration of the N2O and O2 flow-control valves Automatically intercedes to maintain a minimum 25% concentration of oxygen with a maximum N2O:O2 ratio of 3:1
Limitations of Proportioning Systems Machines equipped with proportioning systems can still deliver a hypoxic mixture under the following conditions: Wrong supply gas Defective pneumatics or mechanics (e.g.. The Link-25 depends on a properly functioning second stage regulator) Leak downstream (e.g.. Broken oxygen flow tube) Inert gas administration: Proportioning systems generally link only N2O and O2
Vaporizers A vaporizer is an instrument designed to change a liquid anesthetic agent into its vapor and add a controlled amount of this vapor to the fresh gas flow
Classification of Vaporizers Thermocompensation Supplied heat Temperature compensation Injection Bubble through Flow-over Method of vaporization Measured flow Concentration calibrated (e.g. variable bypass) Methods of regulating output concentration
Generic Bypass Vaporizer Flow from the flowmeters enters the inlet of the vaporizer The function of the concentration control valve is to regulate the amount of flow through the bypass and vaporizing chambers Splitting Ratio = flow though vaporizing chamber/flow through bypass chamber
Factors That Influence Vaporizer Output Flow Rate : The output of the vaporizer is generally less than the dial setting at very low (< 200 ml/min) or very high (> 15 L/min) flows Temperature : Automatic temperature compensating mechanisms in bypass chambers maintain a constant vaporizer output with varying temperatures Back Pressure : Intermittent back pressure (e.g. positive pressure ventilation causes a higher vaporizer output than the dial setting)
Factors That Influence Vaporizer Output Atmospheric Pressure : Changes in atmospheric pressure affect variable bypass vaporizer output as measured by volume % concentration, but not (or very little) as measured by partial pressure (lowering atmospheric pressure increases volume % concentration and vice versa) Carrier Gas : Vaporizers are calibrated for 100% oxygen. Carrier gases other than this result in decreased vaporizer output.
The Circuit: Circle System Arrangement is variable, but to prevent re-breathing of CO2, the following rules must be followed: Unidirectional valves between the patient and the reservoir bag Fresh-gas-flow cannot enter the circuit between the expiratory valve and the patient Adjustable pressure-limiting valve (APL) cannot be located between the patient and the inspiratory valve
Circle System Advantages: Relative stability of inspired concentration Conservation of respiratory moisture and heat Prevention of operating room pollution PaCO2 depends only on ventilation, not fresh gas flow Low fresh gas flows can be used Disadvantages: Complex design = potential for malfunction High resistance (multiple one-way valves) = higher work of breathing
The Adjustable Pressure Limiting (APL) Valve User adjustable valve that releases gases to the scavenging system and is intended to provide control of the pressure in the breathing system Bag-mask Ventilation : Valve is usually left partially open. During inspiration the bag is squeezed pushing gas into the inspiratory limb until the pressure relief is reached, opening the APL valve. Mechanical Ventilation : The APL valve is excluded from the circuit when the selector switch is changed from manual to automatic ventilation
Scavenging Systems Protects the breathing circuit or ventilator from excessive positive or negative pressure .
Scavenging Systems
Checking Anesthesia Machines 8 Categories of check: Emergency ventilation equipment High-Pressure system Low-Pressure system Scavenging system Breathing system Manual and automatic ventilation system Monitors Final Position
The end

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Anesthetic machine for student

  • 1. Introductory Lecture Series: The Anesthesia Machine PORNSIRI WANNADILOK
  • 2. Objectives Anesthesia Machine Ventilators Scavenging Systems System Checkout
  • 3. vaporizer bellow Corrugated tube Soda lime Flow meter ventilator APL valve Scavenging system
  • 4. The Anesthesia Machine High Intermediate Low Pressure Circuit
  • 5. High Pressure System Receives gasses from the high pressure E cylinders attached to the back of the anesthesia machine (2200 psig for O2, 745 psig for N2O) Consists of: Hanger Yolk (reserve gas cylinder holder) Check valve (prevent reverse flow of gas) Cylinder Pressure Indicator (Gauge) Pressure Reducing Device (Regulator) Usually not used, unless pipeline gas supply is off
  • 6. E Size Compressed Gas Cylinders 1800 838 750 2000 Pressure Full (psig) 8.90 8.80 6.76 Full Weight (kg) 5.90 5.90 5.90 5.90 Empty Weight (kg) 625 1590 1590 625 Contents (L) Gas Liquid and gas Liquid and gas Gas State Black/White (yellow) Gray Blue White (green) Color Air Carbon Dioxide Nitrous Oxide Oxygen Cylinder Characteristics
  • 7. Hanger Yolk Hanger Yolk: orients and supports the cylinder, providing a gas-tight seal and ensuring a unidirectional gas flow into the machine Index pins: Pin Index Safety System (PISS) is gas specific prevents accidental rearrangement of cylinders (e.g.. switching O2 and N2O)
  • 8. Pressure Reducing Device Reduces the high and variable pressures found in a cylinder to a lower and more constant pressure found in the anesthesia machine (45 psig) Reducing devices are preset so that the machine uses only gas from the pipeline (wall gas), when the pipeline inlet pressure is 50 psig. This prevents gas use from the cylinder even if the cylinder is left open (i.e. saves the cylinder for backup if the wall gas pipeline fails)
  • 9. Pressure Reducing Device Cylinders should be kept closed routinely. Otherwise, if the wall gas fails, the machine will automatically switch to the cylinder supply without the anesthetist being aware that the wall supply has failed (until the cylinder is empty too).
  • 10. Intermediate Pressure System Receives gasses from the regulator or the hospital pipeline at pressures of 40-55 psig Consists of: Pipeline inlet connections Pipeline pressure indicators Piping Gas power outlet Master switch Oxygen pressure failure devices Oxygen flush Additional reducing devices Flow control valves
  • 11. Pipeline Inlet Connections Mandatory N2O and O2, usually have air and suction too Inlets are non-interchangeable due to specific threading as per the Diameter Index Safety System (DISS) Each inlet must contain a check valve to prevent reverse flow (similar to the cylinder yolk)
  • 12. Oxygen Pressure Failure Devices Machine standard requires that an anesthesia machine be designed so that whenever the oxygen supply pressure is reduced below normal, the oxygen concentration at the common gas outlet does not fall below 19%
  • 13. Oxygen Pressure Failure Devices A Fail-Safe valve is present in the gas line supplying each of the flowmeters except O2. This valve is controlled by the O2 supply pressure and shuts off or proportionately decreases the supply pressure of all other gasses as the O2 supply pressure decreases Historically there are 2 kinds of fail-safe valves Pressure sensor shut-off valve (Ohmeda) Oxygen failure protection device (Drager)
  • 14. Pressure Sensor Shut-Off Valve Oxygen supply pressure opens the valve as long as it is above a pre-set minimum value (e.g.. 20 psig). If the oxygen supply pressure falls below the threshold value the valve closes and the gas in that limb (e.g.. N2O), does not advance to its flow-control valve.
  • 15. Oxygen Failure Protection Device (OFPD) Based on a proportioning principle rather than a shut-off principle The pressure of all gases controlled by the OFPD will decrease proportionately with the oxygen pressure
  • 16. Oxygen Supply Failure Alarm The machine standard specifies that whenever the oxygen supply pressure falls below a manufacturer-specified threshold (usually 30 psig) a medium priority alarm shall blow within 5 seconds.
  • 17. Limitations of Fail-Safe Devices/Alarms Fail-safe valves do not prevent administration of a hypoxic mixture because they depend on pressure and not flow. These devices do not prevent hypoxia from accidents such as pipeline crossovers or a cylinder containing the wrong gas
  • 18. Limitations of Fail-Safe Devices/Alarms These devices prevent hypoxia from some problems occurring upstream in the machine circuitry (disconnected oxygen hose, low oxygen pressure in the pipeline and depletion of the oxygen cylinder) Equipment problems that occur downstream (for example leaks or partial closure of the oxygen flow control valve) are not prevented by these devices.
  • 19. Oxygen Flush Valve (O2+) Receives O2 from pipeline inlet or cylinder reducing device and directs high, unmetered flow directly to the common gas outlet (downstream of the vaporizer) Machine standard requires that the flow be between 35 and 75 L/min The ability to provide jet ventilation Hazards May cause barotrauma Dilution of inhaled anesthetic
  • 20. Second-Stage Reducing Device Located just upstream of the flow control valves Receives gas from the pipeline inlet or the cylinder reducing device and reduces it further to 26 psig for N2O and 14 psig for O2 Purpose is to eliminate fluctuations in pressure supplied to the flow indicators caused by fluctuations in pipeline pressure
  • 21. Low Pressure System Extends from the flow control valves to the common gas outlet Consists of: Flow meters Vaporizer mounting device Check valve Common gas outlet
  • 22. Flowmeter assembly When the flow control valve is opened the gas enters at the bottom and flows up the tube elevating the indicator The indicator floats freely at a point where the downward force on it (gravity) equals the upward force caused by gas molecules hitting the bottom of the float
  • 23. Arrangement of the Flow-Indicator Tubes In the presence of a flowmeter leak (either at the O ring or the glass of the flow tube) a hypoxic mixture is less likely to occur if the O2 flowmeter is downstream of all other flowmeters In A and B a hypoxic mixture can result because a substantial portion of oxygen flow passes through the leak, and all nitrous oxide is directed to the common gas outlet * Note that a leak in the oxygen flowmeter tube can cause a hypoxic mixture, even when oxygen is located in the downstream position
  • 24. Proportioning Systems Mechanical integration of the N2O and O2 flow-control valves Automatically intercedes to maintain a minimum 25% concentration of oxygen with a maximum N2O:O2 ratio of 3:1
  • 25. Limitations of Proportioning Systems Machines equipped with proportioning systems can still deliver a hypoxic mixture under the following conditions: Wrong supply gas Defective pneumatics or mechanics (e.g.. The Link-25 depends on a properly functioning second stage regulator) Leak downstream (e.g.. Broken oxygen flow tube) Inert gas administration: Proportioning systems generally link only N2O and O2
  • 26. Vaporizers A vaporizer is an instrument designed to change a liquid anesthetic agent into its vapor and add a controlled amount of this vapor to the fresh gas flow
  • 27. Classification of Vaporizers Thermocompensation Supplied heat Temperature compensation Injection Bubble through Flow-over Method of vaporization Measured flow Concentration calibrated (e.g. variable bypass) Methods of regulating output concentration
  • 28. Generic Bypass Vaporizer Flow from the flowmeters enters the inlet of the vaporizer The function of the concentration control valve is to regulate the amount of flow through the bypass and vaporizing chambers Splitting Ratio = flow though vaporizing chamber/flow through bypass chamber
  • 29. Factors That Influence Vaporizer Output Flow Rate : The output of the vaporizer is generally less than the dial setting at very low (< 200 ml/min) or very high (> 15 L/min) flows Temperature : Automatic temperature compensating mechanisms in bypass chambers maintain a constant vaporizer output with varying temperatures Back Pressure : Intermittent back pressure (e.g. positive pressure ventilation causes a higher vaporizer output than the dial setting)
  • 30. Factors That Influence Vaporizer Output Atmospheric Pressure : Changes in atmospheric pressure affect variable bypass vaporizer output as measured by volume % concentration, but not (or very little) as measured by partial pressure (lowering atmospheric pressure increases volume % concentration and vice versa) Carrier Gas : Vaporizers are calibrated for 100% oxygen. Carrier gases other than this result in decreased vaporizer output.
  • 31. The Circuit: Circle System Arrangement is variable, but to prevent re-breathing of CO2, the following rules must be followed: Unidirectional valves between the patient and the reservoir bag Fresh-gas-flow cannot enter the circuit between the expiratory valve and the patient Adjustable pressure-limiting valve (APL) cannot be located between the patient and the inspiratory valve
  • 32. Circle System Advantages: Relative stability of inspired concentration Conservation of respiratory moisture and heat Prevention of operating room pollution PaCO2 depends only on ventilation, not fresh gas flow Low fresh gas flows can be used Disadvantages: Complex design = potential for malfunction High resistance (multiple one-way valves) = higher work of breathing
  • 33. The Adjustable Pressure Limiting (APL) Valve User adjustable valve that releases gases to the scavenging system and is intended to provide control of the pressure in the breathing system Bag-mask Ventilation : Valve is usually left partially open. During inspiration the bag is squeezed pushing gas into the inspiratory limb until the pressure relief is reached, opening the APL valve. Mechanical Ventilation : The APL valve is excluded from the circuit when the selector switch is changed from manual to automatic ventilation
  • 34. Scavenging Systems Protects the breathing circuit or ventilator from excessive positive or negative pressure .
  • 36. Checking Anesthesia Machines 8 Categories of check: Emergency ventilation equipment High-Pressure system Low-Pressure system Scavenging system Breathing system Manual and automatic ventilation system Monitors Final Position

Editor's Notes

  1. Mention how the machine is divided into high, intermediate, and low pressure systems
  2. At this point mention that in Sudbury Ontario in the 1970s 23 people died because the N20 and O2 pipelines were crossed over during repairs. Ask them what they would do in this situation? Backup oxygen cylinder turned on Pipeline supply must be disconnected (necessary because the machine will preferentially use the pipeline supply as per the high pressure system regulator design).
  3. The concentration control dial may be located in the bypass chamber of the outlet of the vaporizing chamber Mention that the machine standard requires that all vaporizers on the anesthesia workstation be concentration calibrated (aka variable bypass, direct reading, dial-controlled, automatic plenium, percentage-type, tec-type vaporizers, and vaporizer chamber bypass arrangements
  4. C = concentration at the new atmospheric pressure C = the concentration at the old atmospheric pressure (i.e. the concentration dialed into the vaporizer) P = the barometric pressure for which c is being established P = the barometric pressure for which the vaporizer is calibrated (i.e. at the old atmospheric pressure)
  5. The final three points of the advantages section are meant to contrast with the Bain circuit
  6. Mention that the ventilator relief valve is the same thing as the overflow valve mentioned in the previous slides