What is a comprehensive overview of anesthesia machines?

Comprehensive Overview of Anesthesia Machines

Anesthesia machines are complex workstations that require thorough understanding and regular checking to ensure patient safety during surgical procedures, as failure to properly check and understand these devices has contributed to numerous anesthetic misadventures including hypoxic brain damage and death. 1

Basic Components and Evolution

Anesthesia machines have evolved significantly from simple pneumatic devices of the early 20th century to sophisticated workstations incorporating mechanical, electrical, and electronic components 2. The modern anesthesia workstation originated from modifications to Gwathmey's machine by HEG Boyle in 1917, which became known as the Boyle anesthesia machine 3.

Key Components:

• Gas Supply System
  • Medical gas pipelines
  • Cylinder backups
  • Pressure regulators
  • Flowmeters
• Vaporizer System
  • Temperature-compensated
  • Agent-specific connections
• Breathing Circuit
  • Reservoir bag
  • APL (Adjustable Pressure Limiting) valve
  • CO2 absorber
  • Unidirectional valves
• Ventilator
• Scavenging System
• Monitoring Equipment
• Safety Features

Safety Features

Modern anesthesia machines incorporate numerous safety features that have evolved to prevent critical incidents 4:

1. Oxygen Supply Failure Safety Devices:

   • Oxygen failure warning devices that sound an alarm for at least 7 seconds when oxygen pressure drops 1
   • Gas shut-off mechanisms linked to oxygen supply

2. Oxygen Flush System:

   • Delivers 100% oxygen at 400-500 kPa (58-72.5 PSI)
   • Flow rate of 35-75 L/min
   • Bypasses vaporizers and flowmeters
   • Spring-loaded button that stops when released 5

3. Power Backup Systems:

   • Internal power source providing at least 30 minutes of operation
   • Low and medium priority alarms for power source depletion
   • Continued oxygen supply even during complete power failure 1

4. Pin Index Safety System (PISS) for cylinders

5. Diameter Index Safety System (DISS) for pipeline connections

6. Color-coding of gases and connections

7. Vaporizer Interlocking Mechanisms

8. Pressure Relief Valves

Machine Configurations

Anesthesia machines have two different configurations based on reservoir bag placement 1:

• Left-handed machines (most common): Positioned to the left of the anesthetist
• Right-handed machines: Positioned to the right of the anesthetist

Proper positioning is crucial for ergonomics and safety, as improper placement can lead to awkward reaching and poor monitoring visibility 1.

Pre-Use Checking Procedures

Beginning of Session Checks

The Association of Anaesthetists has established a comprehensive checklist that must be followed at the beginning of each operating session 1:

1. Alternative Ventilation Equipment:

   • Verify self-inflating bag is immediately available
   • Check alternative oxygen source is readily available

2. Machine Check:

   • Perform manufacturer's automated check
   • Verify which checks are included in the automated process

3. Power Supply:

   • Ensure connection to mains electrical supply
   • Verify battery backup is charged
   • Check gas supply master switch is on

4. Gas Supplies and Suction:

   • Perform "tug test" to confirm correct pipeline connections
   • Weekly check of oxygen failure alarm
   • Verify suction equipment functionality

5. Breathing System:

   • Check integrity of circuit
   • Test unidirectional valves
   • Check CO2 absorber

6. Ventilator Settings:

   • Verify appropriate settings for patient
   • Check alarms are properly set

Before Each New Patient

Additional checks must be performed before each new patient or when any alterations are made to the breathing system 1:

1. Check circuit integrity
2. Verify appropriate fresh gas flow
3. Confirm vaporizer settings
4. Test oxygen flush system 5
5. Check monitoring equipment

Common Hazards and Pitfalls

1. Human Factors:

   • Contribute to more complications than machine faults 2
   • Lack of familiarity with equipment
   • Inadequate checking procedures

2. Equipment Issues:

   • Leaks or obstructions from newer components
   • Disconnections during use
   • Power failures
   • Vaporizer malfunctions

3. Environmental Concerns:

   • Trace anesthetic gas pollution
   • Need for efficient scavenging systems 2

Ergonomic Considerations

Proper ergonomics are essential for safe anesthesia delivery 1:

1. Machine Positioning:

   • Ensure appropriate left/right configuration
   • Position to allow easy access to controls and patient
   • Monitor visibility without repeated head turning

2. Electrical Safety:

   • Uninterruptible power supplies for critical equipment
   • Emergency lighting for evacuation routes
   • Ergonomic power switches on devices

3. Workspace Organization:

   • Triangle arrangement between anesthetist, patient, and equipment
   • Trained assistants to hand equipment as needed
   • Easy access to reservoir bag and controls

Modern Anesthesia Systems Classification

Anesthesia systems can be classified according to principles of construction 6:

1. Rebreathing systems (circle systems)
2. Flow- and valve-controlled non-rebreathing systems
3. Systems without reservoirs

This classification is clearer than the traditional closed, semiclosed, semiopen, and open systems categorization 6.

Maintenance Requirements

1. Regular Servicing:

   • Follow manufacturer's recommended intervals
   • Maintain service records
   • Perform thorough "first user" check after servicing 1

2. Documentation:

   • Record all checks performed
   • Document any faults or issues
   • Maintain training records for all users 1

Critical Incident Management

If a critical incident occurs during anesthesia, an immediate check of equipment should be performed even if pre-operative checks were completed, as the incident may be caused by equipment problems that developed during use 1.

Remember that thorough understanding of anesthesia machine components and proper pre-use checking are essential for patient safety. No anesthetist should use equipment without proper training and demonstrated competence 1.