The Anesthesia Gas Machine 2021Historical picture

Michael P. Dosch CRNA PhD, Darin Tharp CRNA MS
University of Detroit Mercy - Nurse Anesthesia
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Copyright Michael P. Dosch. Use for non-profit purposes only is granted.

All sections were revised April 2021.

Please note that this site does not collect confidential, private or semi-private information such as email addresses, email content, or email exchanges with visitors. No data is recorded or stored.

 Section on Using Anesthesia workstations as ICU ventilators added April 2020.



Table of Contents



History of site, Author's Disclosure statement, Acknowledgments, How to contact author, Other resources for learning.

Components and systems

  • Introduction
  • Numbers to remember
  • General features of all anesthesia gas machines
    • Features required by standard
    • Path of gases within the machine
    • Five tasks of oxygen
    • Supply, Processing, Delivery, Disposal model
  • Manufacturers

Supply of

gases & electricity

  • Gas sources
    • Pipeline
    • Cylinders
      • Standards
      • Capacity, color, markings
      • Component parts
      • Storage handling and installation
      • Medical gases
      • Use
  • Electrical power supply
  • Failures and faults (What happens when pipeline oxygen pressure or electrical power is lost?)



Hypoxic guard

  • Fail-safe system
  • Flowmeters
    • How they work
      • Traditional glass flowmeters
      • Transitional (hybrids with needle valve controls, electronic capture and display)
      • Electronic flow control, capture, and display
    • Function (flowmeters for FGF, auxiliary oxygen, scavenging, and common gas outlet)
    • Using flowmeters safely
  • Proportioning systems (Hypoxic guard)


  • Physical principles
  • Classification
  • Vaporizer interlock
  • Operating principles of variable bypass vaporizers
    • Effect of altitude
  • How to fill vaporizers
    • How much liquid agent does a vaporizer use per hour?
  • Hazards and safety features of contemporary vaporizers
  • Current models

Breathing circuits

  • Classification
  • Breathing circuits- Non rebreathing (Mapleson and Bain)
    • How do they work?
    • Fresh gas flow requirements
    • Pethick Test for the Bain Circuit
  • Circle System
    • King (limb within limb)
  • Advantages and disadvantages

CO2 absorption

  • General characteristics and composition
  • Chemistry- soda lime
  • Safe use
    • Changing canisters
    • Clinical signs of exhaustion


  • Classification
    • Bellows classification
  • New ventilator modes and settings (VCV, PCV, PC-VG, SIMV-Vol, SIMV-Pressure, PSV)
  • Typical ventilator alarms
  • New features
    • Piston ventilators
    • Flexibility (New modes)
    • Accuracy at lower tidal volumes
      • Compliance and leak testing
      • Fresh gas decoupling versus compensation
    • Suitability for low flows
  • Current models
    • Dräger Apollo, Perseus, Fabius GS
    • GE ADU, Aisys, Avance, Aespire, Aestiva
    • Other; Paragon, Anestar
  • Older or obsolete ventilators

Using breathing circuits and ventilators

  • Humidification
  • Choosing the best fresh gas flow
    • Low flows
  • How to denitrogenate ("preoxygenate")
  • Malignant hyperthermia implications for equipment.
  • Ventilator and Breathing circuit problems and hazards
    • Increased inspired carbon dioxide (troubleshooting and treatment)


  • Scavenging Systems
    • Purpose
    • Types
    • Practice guidelines
    • Components
    • Hazards
  • Avoiding occupational exposure to waste anesthetic gas

Machine checklist 2008


Cleaning & sterilization

  • Anesthesia gas machine checklist 2008
    • Pre-Anesthesia Checklist (PAC) 2008
    • Electronic checklists- what to add at the end
    • AWS Quick Check for emergencies (and every day)
    • Older anesthesia gas machine checklist
      • Negative pressure leak check
  • Medicolegal
    • Risk management, Quality assurance, Monitoring standards, Manufacturing standards
  • Cleaning and sterilization
    • Sterilization-Moist heat, liquid and gas sterilization methods
    • Care of specific equipment

New gas machines

  • Dräger Medical Inc. (Telford, Pennsylvania)
    • Perseus, Fabius GS, Apollo
  • GE (Madison Wisconsin)
    • Aisys, Avance, Aespire, Aestiva, Aestiva MRI
  • Other
    • Paragon, Anestar
  • Older or obsolete
    • Narkomed (6000/6400, GS, Julian, MRI, Mobile, 2C, 4), Kion, Ohmeda (Modulus SE, Excel 210/110)

Purchasing equipment

  • Education and training
    • Advanced ventilation, Computer and monitor integration, Low flows, Laryngeal mask airway and mechanical ventilation, Electronic Checkout
  • Operating costs
  • Installation of new machines


Test yourself

  • Question and answer format.
Using Anesthesia workstations as ICU ventilators  

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