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  • Oxygen delivery
  • CO2 removal
  • Anesthetic agent administration

See following table.

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Circuit Classifications (Open vs. Closed or Rebreathing vs. Non-Rebreathing)
  • Blowing of oxygen or anesthetic gas over the patient’s face via mask or head drape
No rebreathing
Open drop
  • No longer used. Modern version is the drawover apparatus; useful when compressed gases are not available
Semi-openMapleson breathing systems (A, B, C, D, E, F)
  • Portable, inexpensive but require high fresh gas flow (FGF)
  • Consist of a varied arrangement of FGF, breathing bag, reservoir tubing, expiratory/overflow valve
  • No unidirectional valves, so rebreathing can occur if FGFs are not appropriate
  • Mapleson A: most economic for spontaneous breathing
  • Mapleson D/Bain: most economic for controlled ventilation
SemiclosedCircle system
  • Most common arrangement used in modern anesthesia
  • Because air is rebreathed, CO2 must be removed
  • Considered “semi-open” because there is only partial rebreathing since some gas is lost from the APL/scavenger system
  • Helps to maintain heat, humidity, decrease the required amount of FGF, decrease pollution of atmosphere
ClosedCircle system
  • As above; however, there is total rebreathing of exhaled air (i.e., FGF is approximately equal to patient’s basal O2 requirement with anesthetics)
  • Makes quick changes in gas/anesthetics difficult

See following table.

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Mapleson System Classification
Required fresh gas flows
Mapleson classOther namesConfiguration1SpontaneousControlledComments
AMagill attachment
Equal to minute ventilation (≈80 mL/kg/min)Very high and difficult to predict
  • Most efficient for spontaneous ventilation
  • Poor choice during controlled ventilation
2 × minute ventilation2–2.5 × minute ventilationNot used in modern practice
CWater’s to-and-fro
2 × minute ventilation2–2.5 × minute ventilationNot used in modern practice
2–3 × minute ventilation1–2 × minute ventilationBain coaxial modification: fresh gas tube inside breathing tube (to warm fresh gas). Most efficient for controlled ventilation
EAyre’s T-piece
2–3 × minute ventilation3 × minute ventilation (I:E = 1:2)Exhalation tubing should provide a larger volume than tidal volume to prevent rebreathing. Scavenging is difficult. Decreased resistance in circuit conducive to weaning
FJackson Rees
2–3 × minute ventilation2 × minute ventilationA Mapleson E with a breathing bag connected to the end of the breathing tube to allow controlled ventilation and scavenging. Commonly used for pediatric patients and transportation

1FGI, fresh gas inlet; APL, adjustable pressure limiting (valve).

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Circle System: Essential Components
CharacteristicsPotential hazard
Gas supply
  • Carrier gases (O2, N2O, air) supplied to anesthesia machine via central supply of hospital or portable E cylinders
  • Variable, high-pressure system from cylinders. Regulators decrease pressure to ˜45 psi. Some machines employ a second regulator that further reduces the pressure to ˜12–16 psi
  • Incorrect identification can be fatal
  • Color system for cylinders and hoses (i.e., O2, ...

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