Scavenging

Describe the hazards of anaesthetic gas pollution and the methods of scavenging anaesthetic gases

Scavenging is the removal and safe disposal of waste anaesthesia gases from the breathing circuit to avoid contamination of the theatre environment. This is important as continuous exposure of staff to anaesthetic gases has been implicated in:

• Cognitive impairment
• Spontaneous abortion
• Infertility
• Haematological malignancy

Methods of Scavenging

A scavenging system consists of:

• Gas collection assembly
  • Connects to the APL valve and ventilator relief valve
    Collects gas vented from the circuit.
  • Uses a 30mm connector
    Prevents accidental connection to the breathing system.
• Transfer tubing
• Scavenging interface
  The structure of the scavenging interface depends on the type of scavenging system.
  • Open interface
    Active scavenging systems use a pump to generate a pressure gradient drawing gas to the disposal assembly. The scavenging interface is open to air to prevent the negative pressure being transmitted to the patient.
  • Closed interface
    Passive scavenging systems use a series of positive and negative pressure relief valves.
    • When gas pressure in the collection assembly exceeds 5cmH₂O, the positive relief valve opens and gas enters a reservoir bag
    • When gas pressure in the disposal assembly falls below 0.5cmH₂O, the negative relief valve opens and gas enters the disposal assembly
• More transfer tubing
• Disposal assembly

References

1. Aston D, Rivers A, Dharmadasa A. Equipment in Anaesthesia and Intensive Care: A complete guide for the FRCA. Scion Publishing Ltd. 2014.