How should vaporisers in anaesthesia machines be selected and used?

Vaporiser Selection and Use in Anaesthesia Machines

Vaporisers must be correctly fitted with locking mechanisms fully engaged, adequately filled (but not overfilled), kept strictly upright, and checked for leaks before each use, with manual leak testing only performed on basic Boyle's machines as it may harm modern workstations. 1

Pre-Use Safety Checks

Essential Verification Steps

• Confirm correct vaporiser fitting: Verify the vaporiser for the required volatile agent is fitted correctly to the anaesthetic machine with any locking mechanism fully engaged 1
• Check control knob function: Ensure control knobs rotate fully through the complete range 1
• Verify fill level: Check that vaporisers are adequately filled but not overfilled, and that the filling port is tightly closed 1
• Confirm upright position: Ensure the vaporiser is not tilted, as tilting can result in delivery of dangerously high concentrations of vapour 1
• Turn off vaporisers: After checking, ensure vaporisers are turned off before proceeding 1

Manual Leak Testing Protocol (Basic Machines Only)

Critical caveat: Manual leak testing should only be performed on basic 'Boyle's' machines and may be harmful to many modern anaesthetic workstations—always refer to manufacturer's recommendations before performing manual testing 1

When manual testing is appropriate:

1. Set oxygen flow to 5 L/min with the vaporiser turned off 1
2. Temporarily occlude the common gas outlet 1
3. Confirm no leak from any part of the vaporiser and that the flowmeter bobbin (if present) dips 1
4. When multiple vaporisers are present, turn each vaporiser on in turn and repeat this test 1
5. After testing, ensure vaporisers and flowmeters are turned off 1

Critical Safety Considerations

Non-Interlocked Vaporiser Hazards

Never operate multiple vaporisers simultaneously on non-interlocked systems, as this can result in uncontrolled and potentially lethal concentrations of anaesthetic vapours. 2

Modern anaesthetic workstations often include automatic vaporiser interlocking systems and vaporiser integrity testing that prevent this dangerous scenario 2

Changing or Filling Vaporisers During Use

• Repeat leak testing when changing vaporisers during use whenever possible—failure to do so is a common cause of critical incidents 1
• Only remove a vaporiser from the machine to refill it if the manufacturer specifically recommends this 1
• Vaporisers must always be kept upright during filling and transport 1
• Some modern anaesthetic workstations will automatically test vaporiser integrity after changes 1

Agent-Specific Vaporiser Requirements

Desflurane Vaporisers

Only use a vaporiser specifically designed and designated for desflurane (such as the Tec 6), as desflurane's unique physical properties require electromechanical rather than mechanical controls. 3, 4

The desflurane vaporiser differs fundamentally from conventional vaporisers:

• Uses electromechanical controls to accommodate desflurane's low boiling point 4
• Offers decreased likelihood of accidental delivery of very large concentrations from tilting or overfilling 4
• Incorporates alarms and warnings not found in traditional mechanical vaporisers 4
• Output accuracy is within ±15% in oxygen, similar to mechanical vaporisers 4

Agent-Vaporiser Mismatch

Never mismatch inhaled anaesthetic agents with non-specific vaporisers unless in resource-constrained environments where it is absolutely necessary and no end-tidal anaesthetic gas monitoring is available. 5

This is a dangerous practice that should only be considered in remote locations where neither end-tidal monitoring nor vaporiser-specific agent is available 5

Integration with Two-Bag Test

After individual vaporiser checks, perform the two-bag test to verify complete system integrity:

• Turn on the ventilator to ventilate the test lung 1
• Turn off fresh gas flow or reduce to minimum 1
• Open and close each vaporiser in turn—there should be no loss of volume in the system 1

Common Pitfalls to Avoid

• Failing to check manufacturer recommendations before manual leak testing on modern workstations 1
• Operating multiple non-interlocked vaporisers simultaneously 2
• Tilting vaporisers during filling or transport 1
• Not repeating leak tests after changing vaporisers during use 1
• Overfilling vaporisers or leaving filling ports open 1
• Using non-specific vaporisers for desflurane 3, 4