The Anesthesia Machine and Workstation

Flashcards cover key concepts from The Anesthesia Machine and Workstation, including system components, gas pathways, safety systems, control methods, contemporary workstations, and routine pre-use checks.

What are the main components of the contemporary anesthesia gas delivery system?

The anesthesia machine, anesthesia vaporizer(s), breathing system, ventilator, and waste gas scavenging system.

Why is the breathing system considered the functional center of the anesthesia gas delivery system?

Because it connects to all other components and to the patient, and gas flows back and forth through it during ventilation.

What does CGO stand for and what is its role?

CGO stands for Common Gas Outlet; it delivers the fresh gas mixture from the machine to the patient’s breathing system.

How is gas pressure organized in anesthesia machines? Name the three pressure zones.

High-pressure system (upstream of the first-stage regulator, e.g., 45–2200 psig); Intermediate-pressure system (downstream of the first-stage regulator up to the flow-control valves, 16–55 psig); Low-pressure system (downstream of the flow-control valves, near atmospheric).

What is the Diameter Index Safety System (DISS) and its purpose?

DISS provides gas-specific, noninterchangeable inlet connectors to prevent wrong connections; includes filters and a check valve to prevent gas leakage when the pipeline is disconnected.

What is the function of the first-stage regulator?

To convert high, variable cylinder pressures to a constant lower output pressure (typically around 45 psig) before downstream components.

Describe the oxygen flush and its typical use and risk.

An valve that delivers 35–75 L/min of pure O2 directly to the CGO, bypassing flowmeters and vaporizers; used to fill the breathing system or assist ventilation; can cause dangerous high pressures if used during inspiration.

What is a 'fail-safe' (pressure sensor shut-off) valve and how does it work?

A device that reduces or interrupts the flow of a second gas when the oxygen supply pressure falls below a threshold; not a guaranteed protection against hypoxia; an oxygen analyzer is also needed.

What is the Oxygen Ratio Proportioning System (ORC) and its variants used in modern machines?

A system that prevents hypoxic mixtures by limiting the ratio of O2 to other gases; variants include ORC, S-ORC, and Link-25 Proportioning System.

How do ORC and S-ORC regulate nitrous oxide relative to oxygen?

Two diaphragms control a slave N2O flow valve in series with the N2O flow-control valve to maintain a safe O2:N2O ratio (e.g., not allowing O2 below about 25%); some designs include bypass resistors or different linkage in various brands.

What are Fresh Gas Controllers and Flowmeters, and how do they relate to gas delivery?

Two components deliver each gas: a flow-control device (needle valve or electronic) and a flowmeter (glass rotameter or electronic) to measure and display the flow to the CGO.

What is a rotameter and how does it function?

A vertical glass tube with a float; a constant-pressure, variable-orifice flowmeter; flow is read by float position; gas-specific and orientation must be vertical; not interchangeable between gases.

What is fresh gas decoupling (COSY), and why is it used?

COSY uses extra valves to decouple fresh gas flow from the delivered tidal volume during mechanical ventilation, preventing fresh gas from contributing to tidal volume and improving control of tidal volume and PEEP.

What is the Vaporizer Interlock, and why is it important?

An interlock mechanism that prevents more than one vaporizer from being opened at the same time, preventing simultaneous delivery of multiple agents.

What is the purpose of the CGO outlet check valve?

To prevent backward flow from the CGO toward vaporizers; its presence varies by machine and it helps prevent vaporizer pumping or backflow.

What is the role of pressure sensors and alarms in anesthesia machines?

To monitor pipeline and cylinder pressures and trigger audible/visual alarms when oxygen pressure falls below a preset threshold, ensuring safety.

Why is an oxygen analyzer essential despite fail-safe mechanisms?

Fail-safes monitor oxygen pressure, not all possible gas misconnections; an oxygen analyzer detects crossovers and confirms the actual inspired oxygen concentration.

What is an Auxiliary Common Gas Outlet (ACGO)?

An auxiliary outlet that diverts gas from the main CGO to non-circle systems or to connect devices; can be used for leak testing or specialized gas delivery and is often selectable via a control.

What constitutes the anesthesia machine pre-use checkout?

Ensure manual ventilation capability, verify backup oxygen cylinder and suction, check monitors and alarm settings, confirm vaporizers are filled and leak-checked, test scavenging, and verify CO2 absorbent integrity and spare canisters.

What is the role of second-stage regulators near the flow control valves?

They provide a stable, lower pressure to the flow control valves and flowmeters, ensuring consistent downstream pressure despite variations in supply sources.

What is the Link-25 Proportion Limiting System?

GE’s system that limits the nitrous oxide to oxygen flow ratio to prevent hypoxic mixtures; once the oxygen flow is increased via the linkage, it remains at the increased setting.

What are electronic fresh gas flow meters and their advantages?

Electronic flowmeters use mass flow or differential pressure sensors to measure flow; provide digital readings, data logging, and can support closed-loop control, but require power.

What is the Antihypoxic Device (AHD) in Penlon Prima 400 Series?

A mechanical linkage (gear) between the nitrous oxide control and a slave oxygen control to enforce a minimum oxygen concentration in the delivered gas.

What is the FLOW-i ventilation system’s approach to ventilation and fresh gas?

A turbine-driven or electronically controlled ventilator with a volume reflector, fresh gas compensation, and modular gas flow management; uses electronic vaporizer control and integrated gas modules.

How do modern vaporizers ensure precise anesthetic agent delivery, particularly differentiating between variable bypass and electronic types?

Variable Bypass Vaporizers (e.g., Datex-Ohmeda Tec 5/7, Dräger Vapor 19.1)

1. Mechanism: Rely on temperature and flow compensation. A portion of fresh gas bypasses the vaporizing chamber, while the rest flows through it, picking up agent.
2. Control: Agent concentration is set by a mechanical dial.

Electronic Vaporizers (e.g., Aladin cassette, Maquet FLOW-i)

1. Mechanism: Electronically controlled injection, typically no bypass. They measure flow, temperature, and pressure and inject a precise amount of agent into the fresh gas flow.
2. Advantages: Offer integrated control, automatic agent identification, and high precision, often requiring electrical power.

What is the function of the Adjustable Pressure Limiting (APL) valve in the manual breathing circuit, and how does it operate?

The APL valve is a user-adjustable, pressure-relief valve in the manual breathing system. Its primary functions are:

1. Pressure Protection: It vents excess gas to the scavenging system, protecting the patient from excessive pressure during spontaneous or manual ventilation.
2. Controlled Ventilation: It allows the clinician to control the peak inspiratory pressure during manual bagging by adjusting the resistance to gas outflow.
3. Operation during Mechanical Ventilation: It typically closes or is bypassed during machine ventilation to prevent interference with ventilator-controlled pressures.

What is the purpose of CO\text{2} absorbents in the breathing system, and how do you know when to replace them?

CO\text{2} absorbents (e.g., soda lime, Baralyme, Amsorb) are used to remove carbon dioxide from exhaled gases in a rebreathing circuit. This allows the reuse of other gases (oxygen, anesthetic agents), helping to:

1. Reduce Gas Consumption: Decreases the need for high fresh gas flow.
2. Conserve Heat and Humidity: Maintains patient body temperature and airway moisture.

Replacement Indicators:

• Color Change: Most absorbents contain a pH indicator that changes color (e.g., white to violet, pink to white) when exhausted and saturated with CO\text{2}, signaling the need for replacement.
• Increased Inspired CO\text{2}: Clinical monitoring of inspired CO\text{2} (capnography) will show an increase as the absorbent capacity diminishes.

Describe the components and function of the waste gas scavenging system in an anesthesia machine.

The waste gas scavenging system collects excess anesthetic gases and vapors from the breathing circuit and ventilator, removing them from the operating room environment to protect personnel. It consists of:

1. Gas Collection Assembly: Connects to the APL valve on the manual breathing circuit and the ventilator relief valve.
2. Transfer Tubing: Moves the collected gases to the scavenging interface.
3. Scavenging Interface: This critical component protects the patient's breathing circuit from positive or negative pressure fluctuations that could be caused by the gas disposal system. It can be passive (e.g., open reservoir) or active (e.g., vacuum-driven).
4. Gas Disposal Assembly: Connects to the hospital's central vacuum system (active) or vents to the atmosphere (passive), expelling the waste gases outside the building.

How do modern ventilators (e.g., those with fresh gas decoupling) compensate for fresh gas flow during mechanical ventilation?

Modern ventilators incorporate fresh gas compensation to ensure the delivered tidal volume or pressure remains accurate, independent of the fresh gas flow (FGF) rate. This is achieved through various mechanisms:

1. Fresh Gas Decoupling (COSY): Mechanically separates FGF from the inspiratory limb. A series of valves and a specific internal circuit isolates the ventilator from the FGF during inspiration, preventing FGF from contributing to the delivered tidal volume.
2. Volume Reflector/Absorber: Some systems use a 'volume reflector' bellows or an 'absorber' that allows FGF to enter the inspiratory limb throughout the respiratory cycle but stores excess FGF during expiration, releasing it during the next inspiration to ensure precise volume delivery.
3. Electronic Compensation: Ventilators precisely measure the actual flow and volume delivered to the patient and electronically adjust the breath delivery or account for FGF in their volume calculations, ensuring the set parameters are consistently met. This allows FGF to continue flowing into the circuit during both inspiration and expiration.

What are the main components of the contemporary anesthesia gas delivery system?

The anesthesia machine, anesthesia vaporizer(s), breathing system, ventilator, and waste gas scavenging system.

Why is the breathing system considered the functional center of the anesthesia gas delivery system?

Because it connects to all other components and to the patient, and gas flows back and forth through it during ventilation.

What does CGO stand for and what is its role?

CGO stands for Common Gas Outlet; it delivers the fresh gas mixture from the machine to the patient’s breathing system.

How is gas pressure organized in anesthesia machines? Name the three pressure zones.

High-pressure system (upstream of the first-stage regulator, e.g., 45–2200 psig); Intermediate-pressure system (downstream of the first-stage regulator up to the flow-control valves, 16–55 psig); Low-pressure system (downstream of the flow-control valves, near atmospheric).

What are the key components of the high-pressure system in an anesthesia machine?

The high-pressure system includes gas cylinders (E-cylinders) and their hanger yokes, cylinder pressure gauges, and the first-stage pressure regulators.

What is the purpose of cylinder check valves in the high-pressure system?

They prevent gas from escaping when a cylinder is not present, prevent cross-filling between cylinders, and ensure unidirectional flow from the cylinder to the machine.

What is the Diameter Index Safety System (DISS) and its purpose?

DISS provides gas-specific, noninterchangeable inlet connectors to prevent wrong connections; includes filters and a check valve to prevent gas leakage when the pipeline is disconnected.

What is the function of the first-stage regulator?

To convert high, variable cylinder pressures to a constant lower output pressure (typically around 45 psig) before downstream components.

Describe the oxygen flush and its typical use and risk.

An valve that delivers 35–75 L/min of pure O\text{2} directly to the CGO, bypassing flowmeters and vaporizers; used to fill the breathing system or assist ventilation; can cause dangerous high pressures if used during inspiration.

What is a 'fail-safe' (pressure sensor shut-off) valve and how does it work?

A device that reduces or interrupts the flow of a second gas when the oxygen supply pressure falls below a threshold; not a guaranteed protection against hypoxia; an oxygen analyzer is also needed.

What happens when the oxygen supply pressure fails, and what safety mechanisms alert the user?

When oxygen supply pressure falls (typically below 20-30 psig), a pressure-sensing alarm (oxygen supply failure alarm) activates, and a 'fail-safe' or pressure sensor shut-off valve reduces or interrupts the flow of other gases to prevent hypoxic mixtures.

What is the Oxygen Ratio Proportioning System (ORC) and its variants used in modern machines?

A system that prevents hypoxic mixtures by limiting the ratio of O\text{2} to other gases; variants include ORC, S-ORC, and Link-25 Proportioning System.

How do ORC and S-ORC regulate nitrous oxide relative to oxygen?

Two diaphragms control a slave N\text{2}O flow valve in series with the N\text{2}O flow-control valve to maintain a safe O\text{2}:N\text{2}O ratio (e.g., not allowing O\text{2} below about 25%); some designs include bypass resistors or different linkage in various brands.

What are Fresh Gas Controllers and Flowmeters, and how do they relate to gas delivery?

Two components deliver each gas: a flow-control device (needle valve or electronic) and a flowmeter (glass rotameter or electronic) to measure and display the flow to the CGO.

What is a rotameter and how does it function?

A vertical glass tube with a float; a constant-pressure, variable-orifice flowmeter; flow is read by float position; gas-specific and orientation must be vertical; not interchangeable between gases.

What is fresh gas decoupling (COSY), and why is it used?

COSY uses extra valves to decouple fresh gas flow from the delivered tidal volume during mechanical ventilation, preventing fresh gas from contributing to tidal volume and improving control of tidal volume and PEEP.

What is the Vaporizer Interlock, and why is it important?

An interlock mechanism that prevents more than one vaporizer from being opened at the same time, preventing simultaneous delivery of multiple agents.

What is the purpose of the CGO outlet check valve?

To prevent backward flow from the CGO toward vaporizers; its presence varies by machine and it helps prevent vaporizer pumping or backflow.

What is the role of pressure sensors and alarms in anesthesia machines?

To monitor pipeline and cylinder pressures and trigger audible/visual alarms when oxygen pressure falls below a preset threshold, ensuring safety.

Why is an oxygen analyzer essential despite fail-safe mechanisms?

Fail-safes monitor oxygen pressure, not all possible gas misconnections; an oxygen analyzer detects crossovers and confirms the actual inspired oxygen concentration.

What is an Auxiliary Common Gas Outlet (ACGO)?

An auxiliary outlet that diverts gas from the main CGO to non-circle systems or to connect devices; can be used for leak testing or specialized gas delivery and is often selectable via a control.

What constitutes the anesthesia machine pre-use checkout?

Ensure manual ventilation capability, verify backup oxygen cylinder and suction, check monitors and alarm settings, confirm vaporizers are filled and leak-checked, test scavenging, and verify CO\text{2} absorbent integrity and spare canisters.

What is the role of second-stage regulators near the flow control valves?

They provide a stable, lower pressure to the flow control valves and flowmeters, ensuring consistent downstream pressure despite variations in supply sources.

What is the Link-25 Proportion Limiting System?

GE’s system that limits the nitrous oxide to oxygen flow ratio to prevent hypoxic mixtures; once the oxygen flow is increased via the linkage, it remains at the increased setting.

What are electronic fresh gas flow meters and their advantages?

Electronic flowmeters use mass flow or differential pressure sensors to measure flow; provide digital readings, data logging, and can support closed-loop control, but require power.

What is the Antihypoxic Device (AHD) in Penlon Prima 400 Series?

A mechanical linkage (gear) between the nitrous oxide control and a slave oxygen control to enforce a minimum oxygen concentration in the delivered gas.

What is the FLOW-i ventilation system’s approach to ventilation and fresh gas?

A turbine-driven or electronically controlled ventilator with a volume reflector, fresh gas compensation, and modular gas flow management; uses electronic vaporizer control and integrated gas modules.

How do modern vaporizers ensure precise anesthetic agent delivery, particularly differentiating between variable bypass and electronic types?

Variable Bypass Vaporizers (e.g., Datex-Ohmeda Tec 5/7, Dräger Vapor 19.1)

1. Mechanism: Rely on temperature and flow compensation. A portion of fresh gas bypasses the vaporizing chamber, while the rest flows through it, picking up agent.
2. Control: Agent concentration is set by a mechanical dial.

Electronic Vaporizers (e.g., Aladin cassette, Maquet FLOW-i)

1. Mechanism: Electronically controlled injection, typically no bypass. They measure flow, temperature, and pressure and inject a precise amount of agent into the fresh gas flow.
2. Advantages: Offer integrated control, automatic agent identification, and high precision, often requiring electrical power.

What is the function of the Adjustable Pressure Limiting (APL) valve in the manual breathing circuit, and how does it operate?

The APL valve is a user-adjustable, pressure-relief valve in the manual breathing system. Its primary functions are:

1. Pressure Protection: It vents excess gas to the scavenging system, protecting the patient from excessive pressure during spontaneous or manual ventilation.
2. Controlled Ventilation: It allows the clinician to control the peak inspiratory pressure during manual bagging by adjusting the resistance to gas outflow.
3. Operation during Mechanical Ventilation: It typically closes or is bypassed during machine ventilation to prevent interference with ventilator-controlled pressures.

What is the purpose of CO\text{2} absorbents in the breathing system, and how do you know when to replace them?

CO\text{2} absorbents (e.g., soda lime, Baralyme, Amsorb) are used to remove carbon dioxide from exhaled gases in a rebreathing circuit. This allows the reuse of other gases (oxygen, anesthetic agents), helping to:

1. Reduce Gas Consumption: Decreases the need for high fresh gas flow.
2. Conserve Heat and Humidity: Maintains patient body temperature and airway moisture.

Replacement Indicators:

• Color Change: Most absorbents contain a pH indicator that changes color (e.g., white to violet, pink to white) when exhausted and saturated with CO\text{2}, signaling the need for replacement.
• Increased Inspired CO\text{2}: Clinical monitoring of inspired CO\text{2} (capnography) will show an increase as the absorbent capacity diminishes.

Describe the components and function of the waste gas scavenging system in an anesthesia machine.

The waste gas scavenging system collects excess anesthetic gases and vapors from the breathing circuit and ventilator, removing them from the operating room environment to protect personnel. It consists of:

1. Gas Collection Assembly: Connects to the APL valve on the manual breathing circuit and the ventilator relief valve.
2. Transfer Tubing: Moves the collected gases to the scavenging interface.
3. Scavenging Interface: This critical component protects the patient's breathing circuit from positive or negative pressure fluctuations that could be caused by the gas disposal system. It can be passive (e.g., open reservoir) or active (e.g., vacuum-driven).
4. Gas Disposal Assembly: Connects to the hospital's central vacuum system (active) or vents to the atmosphere (passive), expelling the waste gases outside the building.

How do modern ventilators (e.g., those with fresh gas decoupling) compensate for fresh gas flow during mechanical ventilation?

Modern ventilators incorporate fresh gas compensation to ensure the delivered tidal volume or pressure remains accurate, independent of the fresh gas flow (FGF) rate. This is achieved through various mechanisms:

1. Fresh Gas Decoupling (COSY): Mechanically separates FGF from the inspiratory limb. A series of valves and a specific internal circuit isolates the ventilator from the FGF during inspiration, preventing FGF from contributing to the delivered tidal volume.
2. Volume Reflector/Absorber: Some systems use a 'volume reflector' bellows or an 'absorber' that allows FGF to enter the inspiratory limb throughout the respiratory cycle but stores excess FGF during expiration, releasing it during the next inspiration to ensure precise volume delivery.
3. Electronic Compensation: Ventilators precisely