The Anesthesia Machine and Workstation - Key Concepts

These Q&A flashcards cover the key concepts and components of the anesthesia machine and workstation as described in the notes, including gas pathways, safety features, flow control, vaporizers, breathing systems, and common modern configurations.

What are the main components of a modern anesthesia gas delivery system?

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

Which part of the anesthesia gas delivery system is described as the functional center and why?

The breathing system, because it connects to all other components and to the patient, allowing gas flow to and from the patient.

What is the role of the fresh gas delivery path after leaving the vaporizer?

To mix gases and vaporized anesthetic with oxygen (and other gases) and deliver the result to the patient via the common gas outlet (CGO) into the breathing system.

What does the Diameter Index Safety System (DISS) do in anesthesia machines?

It ensures gas-specific inlet connections so that a pipeline hose cannot be connected to the wrong gas inlet; includes standardized connectors and filtering.

What is the function of the pipeline inlet check valve?

Prevents loss of oxygen when the wall pipeline is disconnected and prevents reverse gas flow into the pipeline.

What does the oxygen supply pressure alarm indicate and when is it activated?

It notifies when the oxygen supply pressure falls below a preset threshold (typically around 30 psig).

Explain an Oxygen Failure Protection Device (OFPD) and when it is used.

A proportional-type pressure-sensor shut-off device used on some Dräger systems that reduces or interrupts (or proportionately reduces) other gases as oxygen pressure drops; ensures some protection against hypoxic delivery.

What is a pressure sensor shut-off (fail-safe) valve, and what is its limitation?

A device that reduces or interrupts the flow of a second gas when oxygen pressure falls below a threshold; it does not guarantee adequate oxygen delivery and is not a true hypoxia safeguard.

What are ORC, S-ORC, and Link-25 systems?

Oxygen ratio proportioning systems that limit the ratio of nitrous oxide to oxygen to prevent hypoxic mixtures; ORC and S-ORC use diaphragms and slave valves or electronic controls, while Link-25 mechanically links oxygen and nitrous oxide flows.

What are the typical inlet pressures to the flowmeters for O2 and N2O from second-stage regulators?

Approximately 14 psig for oxygen and 26 psig for nitrous oxide upstream of their respective flowmeters.

Define the oxygen flush and its cautions.

A valve that delivers 35–75 L/min of pure oxygen directly to the CGO, bypassing flowmeters and vaporizers; can cause very high pressures, risk barotrauma if used during inspiration or in certain ventilator modes.

What are fresh gas controllers and flowmeters composed of?

Two components: a flow-control needle valve (adjustable resistance) and a flowmeter (rotameter or electronic sensor) that measures and displays gas flow.

What is a rotameter, and what principle does it rely on?

A Thorpe-tube style, constant-pressure, variable-orifice flowmeter with a float; flow is governed by laminar or turbulent regime and is gas-specific and calibrated for accurate readings.

Why is the oxygen flowmeter placed on the right side and downstream of other gas flowmeters?

To minimize the chance of delivering a hypoxic mixture if other gas tubes leak; oxygen flow is the last to be affected and is delivered downstream to the CGO.

What is a vaporizer interlock and what does it prevent?

A mechanism that prevents more than one vaporizer from being opened at the same time, avoiding uncontrolled delivery of anesthetic vapor.

What is the purpose of a vaporizer manifold?

A mounting arrangement for concentration-calibrated vaporizers, allowing one vaporizer to be active at a time and permitting quick mounting/dismounting.

What is a CGO outlet check valve and where is it located?

A valve located between the vaporizers and the CGO; it prevents reverse flow from the CGO back toward vaporizers; present on some GE/Mindray machines but not all (e.g., not on Dräger or FLOW-i in some configurations).

What does COSY stand for and what is its purpose?

Fresh gas decoupling breathing system (COSY II/2.5/2.6); removes fresh gas flow from contributing to delivered tidal volume during mechanical ventilation by using a decoupler and additional valves.

How does a COSY breathing system differ from a standard circle system during mechanical ventilation?

Only the patient-side portion is pressurized on inspiration; the fresh gas decoupler and extra valves remove fresh gas from influencing tidal volume, and the absorber and fresh gas inlet remain at near-atmospheric pressure.

What is the function of the ventilator’s PEEP/PEmax valve?

To determine positive end-expiratory pressure (PEEP) and maximum airway pressure (PEmax) during ventilation, helping protect the patient and limiting peak pressures.

How do mechanical flow-control valves differ from electronic flow-control valves?

Mechanical flow-control valves use manual needle valves to set orifice size and rely on pressure differences; electronic flow-control valves use a computer to control flow with feedback from downstream sensors, limiting hypoxic risks and enabling closed-loop control.

What are electronic flowmeters and what are their benefits and requirements?

Flowmeters that use mass flow or differential pressure transducers to measure gas flow, with digital or virtual readouts; enable data logging and automated control but require electrical power.

What is the purpose of an auxiliary common gas outlet (ACGO)?

An optional outlet that provides an alternative connection for non-circle breathing systems or for low-pressure testing, jet ventilation, or delivering gas to devices outside the standard circle system.

What should be included in a thorough pre-use checkout of an anesthesia workstation?

Ensure manual ventilation capability (e.g., a functioning bag), verify patient suction, confirm monitors and alarm settings, ensure backup oxygen cylinder is available and full, check vaporizers for leaks, verify scavenging system operation, confirm CO2 absorbent status and stock spare canisters, and perform leak checks; follow institutional procedures and ASA guidelines.

What is the Anti-Hypoxic Device (AHD) in Penlon Prima series, and what does it do?

A gear-linked mechanism that ensures a minimum oxygen concentration by coupling the nitrous oxide control to a slave oxygen control, thereby maintaining a safe O2 proportion.

What is the Flow-i’s unique driving gas arrangement and how does it handle power failure?

Flow-i uses electronic gas modules with a drive gas that is typically oxygen; in power failure, the system fails safe and may require a backup battery; if battery is depleted, alternate gas control may activate (depending on model).

What is the Pin Index Safety System (PISS) and for what is it used?

A safety system using a specific pattern of two pins on the yoke assembly to uniquely fit a matching pattern of holes on the cylinder valve, preventing incorrect gas cylinder attachment (e.g., an oxygen cylinder cannot be mistakenly attached to a nitrous oxide yoke).

What are the typical full tank pressures for an E-cylinder of oxygen and nitrous oxide?

For oxygen, approximately 2200 \text{ psig}. For nitrous oxide, approximately 745 \text{ psig} (due to it being a liquid at room temperature).

What is the function of a cylinder pressure regulator on an anesthesia machine?

It reduces the high and variable pressure from the gas cylinder (e.g., 2200 \text{ psig} oxygen) to a constant, lower, and safer working pressure (typically 45 \text{ to } 50 \text{ psig}) for delivery to the machine's intermediate pressure system.

Describe the function of cylinder check valves.

Cylinder check valves are located downstream of the gas cylinder and upstream of the pressure regulator; they allow gas to flow from the cylinder into the machine but prevent reverse flow into the cylinder and prevent gas leakage from an empty or disconnected cylinder port when the other cylinder is in use.

What is the pipeline inlet pressure typically supplied to the anesthesia machine?

Typically between 45 \text{ and } 55 \text{ psig} for both oxygen and nitrous oxide, provided by the hospital's central gas supply.

Where are pipeline pressure gauges usually located, and what do they indicate?

They are typically located on the front panel of the anesthesia machine (often near the gas inlets) and indicate the pressure of the gas being supplied from the pipeline source to the machine's internal system.

What is the purpose of a second-stage regulator in an anesthesia machine?

Second-stage regulators further reduce gas pressure (e.g., oxygen to 14 \text{ psig}, nitrous oxide to 26 \text{ psig}) before the gases enter their respective flowmeters, ensuring consistent and precise flow control regardless of slight variations in upstream pressure.

Explain what constitutes the 'intermediate pressure system' of an anesthesia machine.

The intermediate pressure system includes components that receive gas at slightly above atmospheric pressure (around 45-55 \text{ psig}) from either the pipeline or cylinder regulators. It typically includes the pipeline inlet connections/check valves, pressure gauges, oxygen pressure failure devices, second-stage regulators, and the oxygen flush valve.

What does an anesthesia machine's master switch do?

The master switch activates pneumatic and electrical systems of the anesthesia machine, including controls for gas flow, vaporizers, patient monitors, and alarms.

How does an anesthesia machine prioritize gas sources between pipeline and cylinders?

Most modern machines are designed to preferentially draw gas from the pipeline supply when connected and available, as pipeline pressure is typically higher and more consistent than cylinder pressure after regulation. Cylinders serve as backup.