Learning objectives

• Describe the purpose and composition of closed circle anesthesia
• Describe the technique and safety precautions of closed circle anesthesia
• Describe the advantages and disadvantages of closed circle anesthesia

Background

• The current inhalational anesthetic agents with low blood solubility sparked renewed interest in closed circle anesthesia, due to their cost and environmental concerns
• The circle system’s components are arranged in a circular manner
• The system allows rebreathing of anesthetic agents while avoiding rebreathing of CO2
• This allows the use of low or minimal fresh gas flow

System composition

• The circle system consists of:
  • Fresh gas flow (FGF)
  • Inspiratory and expiratory unidirectional valves
  • Inspiratory and expiratory tubing
  • Y-piece connector
  • APL valve
  • Reservoir bag
  • CO2 absorber
• The most efficient arrangement:
  • FGF enters the system before the inspiratory unidirectional valve
  • The APL valve and reservoir are situated between the expiratory valve and the CO2 absorber
  • The CO2 absorber is situated before the FGF entry point

Definitions

• Closed circle anesthesia: 
  • FGF is just sufficient to replace the volume of gas and vapor absorbed by the patient (Basal oxygen requirements, volatile agent uptake, and nitrous oxide uptake if used)
  • No gas leaves through the APL valve
  • Exhaled gases are rebreathed after CO2 absorption
• Low flow anesthesia
  • FGF < alveolar ventilation (usually < 1.5 L/min)
  • Excess gases are eliminated via the APL valve
• Ultra-low flow anesthesia
  • FGF < 0.5 L/min
  • Excess gases are eliminated via the APL valve

Technique

Safety

• Monitor inspired oxygen, end-tidal carbon dioxide, and inhalational agent
• Prevent unidirectional valves from sticking due to water vapor condensation
• Resistance to breathing is increased during spontaneous ventilation due to the unidirectional valves
• Prevent compound A formation: Newer designs of soda lime claim less or no production of compound A, baralyme is worse than soda lime, and Amsorb© is the safest
• Methane, acetone, ethanol, and hydrogen can accumulate but generally do not become clinically significant
• Uneven filling of the canister with soda lime leads to channeling of gases and reduced efficiency
• There is an increased potential for leads and disconnection due to the many connections

Advantages & disadvantages

Suggested reading

• Pollard BJ, Kitchen, G. Handbook of Clinical Anaesthesia. Fourth Edition. CRC Press. 2018. 978-1-4987-6289-2.
• Herbert L, Magee P. Circle systems and low-flow anaesthesia. BJA Education. 2017;17(9):301-5.

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