page_title: Breathing circuit
section_title: Types
hierarchical_section_title: Breathing circuit / Types
caption_attribution_description: Examples of anaesthetic breathing systems that are commercially manufactured. From top to bottom: a Mapelson C system manufactured by Intersurgical; a Mapelson E system (also known as Ayre's T-piece), to which a Venturi valve has been fitted so as to reduce the delivered oxygen concentration; and a Mapelson F system (also known as the Jackson-Rees modification of Ayre's T-piece) manufactured by Intersurgical.
context_page_description: A breathing system or breathing circuit is a medical device used to deliver oxygen, remove carbon dioxide, and deliver inhalational anaesthetic agents to a patient. Originally developed for use in anaesthesiology, many variants of breathing system are in clinical use, but most comprise a source of fresh gas flow, a length of breathing tubing to direct the gas, an adjustable pressure limiting valve to control pressure within the system and direct waste away, and a reservoir bag to allow assisted ventilation.
context_section_description: There are many forms of breathing system, each having somewhat different mechanisms of action. They have traditionally been classified by the way in which the system interacts with fresh air from the surrounding atmosphere, and by whether the patient rebreathes gases that they have previously exhaled. However, there is no international standard for classifying breathing systems, and the terms "semi-open" and "semi-closed" may cause confusion in particular between US and British usage. Strictly speaking, the term "circuit" is only accurate in the case of closed systems where the breathed gas completes a full circuit.
  Open systems use unrestricted ambient air as the source of fresh gas, with no boundary between the patient's airway and the atmosphere. Purely open systems - for instance, gauze soaked in ether by the open-drop technique and held near the patient's face - are archaic and are no longer in clinical use. They have no reservoir and no rebreathing takes place.
  Semi-open systems such as the Schimmelbusch mask use ambient air as the fresh gas source, but incorporate some sort of apparatus or reservoir that restricts the supply by creating a partial boundary with the atmosphere. No rebreathing occurs.
  Semi-closed systems have a full boundary with the surrounding atmosphere, and use a controlled source for fresh gas flow. Intake of ambient air is prevented, but excess fresh gas is vented into the surrounding atmosphere. Partial rebreathing of exhaled gas can occur. They are commonly subdivided using the Mapelson classification (see below).
  Closed systems have a totally closed boundary across which no gas enters or is vented, meaning that complete rebreathing takes place. The commonest example is the circle system.
caption: Examples of commercially available anaesthetic breathing systems. From top to bottom: a Mapelson C system manufactured by Intersurgical; a Mapelson E system, to which a red Venturi valve has been fitted so as to reduce the delivered oxygen concentration; and a Mapelson F system manufactured by Intersurgical.
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