Scavening

• Scavenging system


  Collects and discards waste anesthetic gases safely

  
• Scavenging system

  • Should not affect the ventilation and oxygenation of the patient
  • Should not affect the dynamics of the breathing

  
• Basic components of any type of scavenger


  • Collecting and transfer system
  • Receiving system
  • Disposal system

  
• Open scavenging system


  Uses a reservoir to collect waste gas, which is then actively suctioned from the reservoir. The reservoir communicates with the atmosphere and requires no pressure relieving valve.
• Closed scavenging system


  Not connected to the atmosphere of the OR but waste gas exits the machine and then the OR through a series of valves. Must have both positive- and negative-pressure relief valves.

  
• Types of closed scavenging system

  • Active via means of suction
  • Passive, relying on heavier-than-air anesthesia gases and pressure to move waste gas to evacuation

  
• Passive scavenging system

  • Simple
  • Low cost
  • Require positive and negative pressure relieving valve for protection from collapse and barotrauma
  • Outlet may be a direct line to the outside via a ventilation duct beyond any point of recirculation

  
• Components of passive scavenging system

  • Collecting and transfer system
  • Receiving system (reservoir bag)
  • Disposal system (wide-bore copper pipe)

  
• Mechanism of passive scavenging system


  1. Exhaled gases are driven by either the patient's respiratory efforts or the ventilator

  2. Receiving system should be mounted on the anesthetic machine to minimize the length of transfer tubing and resistance to flow

  
• Problems in practice and safety features of passive scavenging system
• Components of active scavenging system


  • Collecting and transfer system
  • Receiving system (valveless, open-ended reservoir)
  • Active disposal system (fan or pump to generate vacuum)

  
• Mechanism of active scavenging system


  1. Vacuum drives the gases through the system

  2. Able to deal with a wide range of expiratory flow rates (30–130 L/min)

  3. Receiving system is capable of coping with changes in gas flow rates

  
• Problems in use of active scavenging system
• Scavenging system checkout


  • Ensure proper connections
  • Adjust waste-gas vacuum (if possible)
  • Fully open APL valve and occlude Y-piece
  • With minimum O2 flow, allow scavenger reservoir bag to collapse completely and verify absorber pressure gauge reads about zero
  • With the O2 flush activated, allow scavenger reservoir bag to distend fully, and then verify absorber pressure gauge reads <10 cm H2O

  
• Charcoal canisters (Cardiff Aldasorber)


  Compact passive scavenging system that absorbs halogenated inhalational agents
• Problems and safety features of charcoal canisters