Anesthesia Breathing Systems
M Ravi Shankar MD

Bhavani Shankar Kodali MD

Professor and Chair of Anesthesia,

Associate Professor

JIPMER, Pondicherry, India

Harvard Medical School, Boston, MA 


For a comprehensive understanding of 'Anesthesia breathing circuits' click here for a review. It opens a new window, close the window to return to this section again. 

The following section contains pertinent features of anesthesia circuits and their functional analysis for easy understanding facilitated by animations.  



A breathing system is defined as an assembly of components which connects the patientís airway to the anaesthetic machine creating an artificial atmosphere, from and into which the patient breathes.

It primarily consists of

a) A fresh gas entry port/delivery tube through which the gases are delivered from the  machine to the systems;

b) A port to connect it to the patientís airway;

c) A reservoir for gas, in the form of a bag or a corrugated tube to meet the peak inspiratory flow requirements;

d) An expiratory port/valve through which the expired gas is vented to the atmosphere;

e) A carbon dioxide absorber if total rebreathing is to be allowed and

f) Corrugated tubes for connecting these components.

       Flow directing valves may or may not be used.




Unidirectional flow:

a) Non rebreathing systems.

B) Circle systems.


Unidirectional flow

Circle system with absorber.



Bi-directional flow:

a) Afferent reservoir systems.

Mapleson A

Mapleson B

Mapleson C

Lackís system.

B) Enclosed afferent reservoir systems

Millerís (1988)

c) Efferent reservoir systems

Mapleson D

Mapleson E

Mapleson F

Bainís system

d) Combined systems

Humphrey ADE

Bi-directional flow

To and Fro system.
















Mapleson circuits 


In 1954 Mapleson described and analyzed five different semiclosed anesthetic systems, and they are classically referred to as Mapleson systems and designated A to E. In 19  , Willis et al added the F system to the five original systems. The table below shows appearance and description of each system.  For functional analysis of each of these systems, click on the hyperlink to open a new window. Close the window to return back to this section.


Fresh gases              CO2 containing gases                  There is mixing of these two in rebreathing systems

Type  Appearance Description
Mapleson A Expiratory valve close to face mask, separated by corrugated tube (    ) from reservoir bag and supply of fresh gases






Mapleson B Expiratory valve and supply of fresh gases close to face mask, separated by corrugated tube  (    ) from reservoir bag






Mapleson C Expiratory valve,  supply of fresh gases and reservoir bag , all close to face mask (No corrugated tube (    )






Mapleson D Supply of fresh gases close to face mask, separated by corrugated tube (    ) from reservoir bag and expiratory valve





Mapleson E Supply of fresh gases close to face mask. Open length of corrugated tube (    ). No reservoir bag or expiratory valve.






Mapleson F Supply of fresh gases close to face mask. Corrugated tube (    ) present. . Reservoir bag with expiratory port, but no expiratory valve.

Mapelson E with reservoir bag.




Relative efficiency of rebreathing among various Mapleson circuits

Spontaneous ventilation


Controlled ventilation


Mapleson A  is most efficient during spontaneous ventilation. It is worst for controlled ventilation.
Mapleson D is most efficient during controlled ventilation


Circle system

This is unidirectional breathing system with CO2 absorption. It consists of inspiratory unidirectional valve, inspiratory limb, expiratory limb, expiratory unidirectional valve, expiratory pop off valve, reservoir bag, CO2 absorber, fresh gas in flow.


Bain system

This is a modified Mapleson D system, with fresh gas flow delivery tube running inside of the expiratory limb


Non rebreathing system

This is a unidirectional non rebreathing system with out CO2 absorption. A non rebreathing valve is located near the patient end.


For other circuits refer to the monogram.