The Anesthesia Machine and Workstation - Chapter 2

Function: Receive compressed gases from suppliers or cylinders to create a gas mixture of known composition and flow rate at the Common Gas Outlet (CGO).
Safety features: Designed to prevent delivery of a hypoxic mixture to the breathing system.
Key subsystems:
- Gas flow proportioning system
- Pressure sensor shut-off (fail-safe) system that interrupts or proportionally reduces and ultimately interrupts the supply of nitrous oxide (N2O) and other gases to their flow meters.
- Gas inlets, DISS (Diameter Index Safety System), gas-specific connections.
- Gauges and sensors to monitor system status.

Pressure Regulators: Convert a variable high input gas pressure to a constant, lower output pressure.
Common Gas Outlet (CGO): Receives the gas output from the anesthesia machine for delivery to the anesthesia circuit.

Function: Pressing the O2 flush results in a high-flow of pure oxygen.
- Flow rate: 35-75\ \text{L/min} of O2.
Uses:
- Fill the breathing system with O2 to manually ventilate the patient.
- Provide high-pressure O2 for emergency jet ventilation.
Risks:
- Barotrauma: injury to lung tissue caused by high pressure if used inappropriately.

Mechanical Flow Meter (rotameters): Display the flow of a specific gas in liters per minute (\text{L/min}).
Types: Mechanical or electronic.
Rotameters:
- Vertical glass tubes calibrated for specific gases.
- Use a unique float.
- Calibration is specific to a certain range of temperature and pressure.

Central component of the anesthesia gas delivery system.
Connects to all other components and to the patient.
Described as a simple and logical device that forms the interface between machine and patient.

Purpose: Provide support and enhance the patient’s breathing pattern.
Function: Delivers and removes anesthetic gases via the breathing system.
Modes:
- Pressure Control: A set inspiratory pressure is delivered.
- Volume Control: A set tidal volume is delivered.

Purpose: Remove waste anesthetic gases (WAGs) from the operating room.
Types:
- Active scavenging: requires suction.
- Passive scavenging: relies on passive flow downstream of the system.
Operation: Collects WAGs from the breathing circuit and discards them.
Pathway: WAGs exit the breathing system via the APL (Adjustable Pressure-Limiting) valve.

Function: Convert volatile anesthetic medication from a liquid to a set concentration of gas delivered to the patient.
Design: Each vaporizer is designed to hold only one specific volatile agent and is clearly labeled.

System shown with a dial and label references (example markings observed):
- Digits/labels such as: 123215896, 18-8226-20, Usual dosage: e, 030N, W, Off
- Manufacturer references observed: Datex-Ohmeda, Sevotec 5, LINGAL TECHNOLOGY, SHC 5381, NGAL TECHNOLOGY
- Agent indication: Use Only Sevoflurane
Interpretation:
- The key-filling system is used to set and fill the vaporizer with the appropriate volatile agent (e.g., Sevoflurane) and dosage parameters.
- The labels indicate agent type, dosage settings, and safety indicators.

Purpose: Provide vital information to ensure safe care of the patient.
Gas analyzers: Monitor volatile agents (e.g., Sevoflurane, Isoflurane, Desflurane).
Electrocardiography (ECG): Monitors electrical activity of the heart.
Pulse Oximetry: Measures arterial oxygen saturation.
Non-Invasive Blood Pressure (NBP): Monitors blood pressure non-invasively.
Capnography: Measures inspired and expired CO2 concentrations.
Temperature monitoring: Monitors patient temperature.

Safety emphasis: Prevent hypoxic gas mixtures; monitor gas concentrations and patient parameters continuously.
O2 flush use considerations: High flow can rapidly change gas composition and pressure; improper use can cause barotrauma or hemodynamic changes.
WAG management: Proper scavenging reduces occupational exposure and environmental impact.
System integration: All components (gas delivery, vaporizers, breathing system, ventilator, scavenging, monitoring) must function cohesively to maintain safe anesthesia delivery.

Hypoxic Mixture Prevention: The machine’s fail-safe and proportioning systems help ensure N2O and other gases do not dilute oxygen below safe levels.
Emergency Ventilation: O2 flush and high-flow capabilities provide rapid oxygenation when needed, but must be used with awareness of potential barotrauma.
Ventilator Modes: Selecting Pressure vs. Volume control affects peak pressures, tidal volumes, and gas uptake; choose based on patient size, lung compliance, and surgical factors.
Monitoring Redundancy: Gas analyzers, ECG, SpO2, NBP, capnography, and temperature provide complementary safety data; deviations should trigger corrective actions.

Oxygen flush flow: Q_{O2} = 35 \text{-} 75 \ \text{L/min}
No other explicit formulas provided in the transcript; rely on standard anesthesia practice for calculations involving tidal volume, respiratory rate, and vaporizer settings as per clinical context.

Gas properties and safety: Pressure regulation, flow measurement, and gas mixing principles underpin the machine’s design.
Patient safety: Redundancies (fail-safes, DISS, CGO, scavenging) reflect foundational clinical safety ethics in anesthesia.
Pharmacology of volatile agents: Vaporizers deliver precise agents (e.g., Sevoflurane) with labeled dosing to ensure controlled anesthesia depth.

Ethical responsibility to minimize patient risk via engineering controls and monitoring.
Environmental and occupational health considerations through effective waste gas scavenging.
Practical training implications: Operators must understand each subsystem, its safety features, and potential failure modes to respond appropriately during anesthesia.