Skip to Main Content


  • Oxygen delivery
  • CO2 removal
  • Anesthetic agent administration


See following table.

Table Graphic Jump Location
Favorite Table | Download (.pdf) | Print
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.

Table Graphic Jump Location
Favorite Table | Download (.pdf) | Print
Mapleson System Classification
Required fresh gas flows
Mapleson classOther namesConfiguration1SpontaneousControlledComments
AMagill attachmentImage not available.Equal to minute ventilation (≈80 mL/kg/min)Very high and difficult to predict
  • Most efficient for spontaneous ventilation
  • Poor choice during controlled ventilation
BImage not available.2 × minute ventilation2–2.5 × minute ventilationNot used in modern practice
CWater’s to-and-froImage not available.2 × minute ventilation2–2.5 × minute ventilationNot used in modern practice
DBainImage not available.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-pieceImage not available.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 ReesImage not available.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).

Table Graphic Jump Location
Favorite Table | Download (.pdf) | Print
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 ...

Want remote access to your institution's subscription?

Sign in to your MyAccess profile while you are actively authenticated on this site via your institution (you will be able to verify this by looking at the top right corner of the screen - if you see your institution's name, you are authenticated). Once logged in to your MyAccess profile, you will be able to access your institution's subscription for 90 days from any location. You must be logged in while authenticated at least once every 90 days to maintain this remote access.


About MyAccess

If your institution subscribes to this resource, and you don't have a MyAccess profile, please contact your library's reference desk for information on how to gain access to this resource from off-campus.

Subscription Options

AccessAnesthesiology Full Site: One-Year Subscription

Connect to the full suite of AccessAnesthesiology content and resources including procedural videos, interactive self-assessment, real-life cases, 20+ textbooks, and more

$995 USD
Buy Now

Pay Per View: Timed Access to all of AccessAnesthesiology

24 Hour Subscription $34.95

Buy Now

48 Hour Subscription $54.95

Buy Now

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.