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Mapleson circuits in anesthesia

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Mapleson circuits anesthesia classification types fresh gas flow

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Mapleson Circuits in Anesthesia

Overview

Mapleson circuits (also called Mapleson breathing systems) are a group of semi-open, non-rebreathing anesthesia circuits first described by W.W. Mapleson in 1954. They consist of simple components arranged in different configurations - and it is the relative position of each component that determines circuit performance. A sixth system (F) was later added by Willis et al.
They differ fundamentally from the circle system in two ways: gas flow is bidirectional, and there is no CO2 absorber - CO2 elimination depends entirely on sufficient fresh gas inflow (washout).

Components

All Mapleson circuits share the same basic building blocks:
  • Corrugated breathing tubes (22 mm diameter) - large bore to minimize resistance; also act as a gas reservoir. Volume should ideally equal or exceed the patient's tidal volume.
  • Fresh gas inlet (FGI) - continuously supplies anesthetic gas mixture from the machine.
  • Adjustable Pressure-Limiting (APL) valve - the "pop-off" or pressure-relief valve; vents excess gas and prevents pressure buildup.
  • Reservoir bag - acts as a buffer for gas supply and allows manual ventilation (absent in Mapleson E).
  • Face mask or ETT connection - patient interface.
The position of the FGI relative to the APL valve is the primary determinant of circuit efficiency.
  • Morgan & Mikhail's Clinical Anesthesiology, 7e, p. 83-85

Classification Table

The six circuits (A-F) differ in component arrangement:
Mapleson Classification Table - configurations and required fresh gas flows
Table from Morgan & Mikhail's Clinical Anesthesiology, 7e

Gas Flow Diagrams (All Six Circuits)

The diagram below shows gas distribution at end-expiration for each circuit (blue = fresh gas, orange = dead space gas, red = alveolar gas):
Mapleson A-F breathing systems showing gas distribution
From Miller's Anesthesia, 10e (Fig. 20.38)

Individual Circuits

Mapleson A - "Magill Attachment"

  • FGI at the bag end (far from patient); APL valve near the patient/mask.
  • The only circuit where FGI is far from the patient.
  • Spontaneous ventilation: Most efficient of all Mapleson circuits. FGF equal to minute ventilation (~80 mL/kg/min) is sufficient. During expiration, alveolar gas is vented through the APL valve, and fresh gas fills the tube before the next breath.
  • Controlled ventilation: Least efficient - requires very high FGF (>3× minute ventilation) because the APL valve must be partially closed, preventing venting during expiration.
  • Rarely used today for controlled ventilation; a poor choice for IPPV.

Mapleson B

  • FGI and APL valve are both near the patient end.
  • Spontaneous: 2× minute ventilation.
  • Controlled: 2-2.5× minute ventilation.
  • Mixed gas accumulates in the reservoir bag, making efficiency intermediate.
  • Rarely used clinically.

Mapleson C - "Waters' To-and-Fro"

  • Similar to B but lacks the corrugated reservoir tube (no breathing tube between bag and patient).
  • Spontaneous: 2× minute ventilation.
  • Controlled: 2-2.5× minute ventilation.
  • Compact but dead space is a concern.

Mapleson D - "Bain Circuit" (coaxial modification)

  • FGI near the patient end; APL valve near the bag (opposite of A).
  • Functionally the mirror image of A.
  • Spontaneous: 2-3× minute ventilation (less efficient than A for spontaneous).
  • Controlled: 1-2× minute ventilation - most efficient of all Mapleson circuits for controlled ventilation. Fresh gas pushes alveolar gas away from the patient toward the APL valve.
  • Bain circuit: A coaxial modification where the FGI tube runs inside the outer corrugated breathing tube. Benefits include: compactness, partial heat/humidity conservation (countercurrent exchange between warm expired and cool inspired gas). Key hazard: unrecognized kinking or disconnection of the inner tube causes hypercapnia. The Pethick test checks inner tube integrity.

Mapleson E - "Ayre's T-piece"

  • A simple T-piece: FGI at the patient end, open-ended expiratory limb (no bag, no APL valve).
  • No reservoir bag - only supports spontaneous ventilation (the only Mapleson without a bag). Used to liberate ICU patients from mechanical ventilation.
  • Expiratory limb volume must exceed tidal volume to prevent rebreathing.
  • Spontaneous: 2-3× minute ventilation.
  • Controlled: ~3× minute ventilation (I:E ratio 1:2).
  • Scavenging is difficult with this system.

Mapleson F - "Jackson-Rees Circuit"

  • Mapleson E with a breathing bag added to the distal end, plus a valve to vent excess gas.
  • FGI at the patient end; APL valve (or open tail) at the bag end.
  • Primary pediatric circuit - low resistance, minimal dead space.
  • The bag allows controlled ventilation and manual PEEP, plus monitoring of breathing by watching bag movement.
  • FGF to prevent rebreathing: ~2.5× minute ventilation (same as Mapleson D).
  • Also used for patient transport.

Functional Groups

Barash groups them into three performance clusters:
GroupMembersNotes
Group AMapleson ABest for spontaneous; worst for controlled
Group B/CMapleson B, CIntermediate efficiency both modes
Group D/E/FMapleson D, E, FBest for controlled; moderate for spontaneous
  • Barash Clinical Anesthesia, 9e, p. 2010

Key Performance Principle

"Simply moving components completely alters the fresh gas requirements."
  • Morgan & Mikhail's Clinical Anesthesiology, 7e, p. 88
Memory aid for FGF requirements:
CircuitSpontaneousControlled
A= MV (most efficient)>3× MV (worst)
B, C2× MV2-2.5× MV
D, E, F2-3× MV1-2.5× MV (D/F most efficient)
MV = minute ventilation (~70-80 mL/kg/min in adults)

Advantages of Mapleson Systems

  • Lightweight, inexpensive, simple with few parts
  • Low resistance to gas flow
  • Rapid changes in FGF concentration translate quickly to the patient (no absorber)
  • No CO2 absorber means no volatile anesthetic degradation (e.g., no compound A with sevoflurane)
  • Small dead space (important in pediatrics)

Disadvantages

  • Higher FGF required vs. circle systems - less economical, more waste gas
  • Poor heat and humidity conservation
  • Scavenging is challenging (especially Mapleson E)
  • No rebreathing means higher volatile anesthetic consumption
  • Risk of awareness if FGF is inadequate

Clinical Uses Today

  • Mapleson D / Bain: Still commonly used intraoperatively, especially for controlled ventilation; popular in the UK and Canada
  • Mapleson E / F (Jackson-Rees): Pediatric anesthesia, patient transport, ICU ventilator weaning
  • Mapleson A, B, C: Largely historic; rarely used in modern practice
  • All systems remain useful in resource-limited settings
  • Miller's Anesthesia, 10e, p. 2351-2353
  • Barash Clinical Anesthesia, 9e, p. 2010-2013
  • Morgan & Mikhail's Clinical Anesthesiology, 7e, p. 83-88
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