ANESTHESIA EQUIPMENT:
Breathing Circuits & Scavenging System
(
Lecture 9 printable version)

Lyon Lee DVM PhD DACVA

Introduction

Figure 1 - The Circle Breathing System

Figure 2 - Non-rebreathing circuits

Current terminology of the Anesthetic breathing circuits

Non-rebreathing circuits

Rebreathing circuits

Old Terminology of the Anesthetic breathing circuits

There are exceptions but basically all systems using non compressed gases (i.e. room air) classify as ‘open’ and all those using an oxygen cylinder classify as ‘closed’.

Table 1. Traditional terminology of the anesthetic breathing circuits.

 

Reservoir

Rebreathing

Types

1. Open. Draw over systems with non rebreathing valves.

No

No

Bag and bottle

2. Semi‑open.

No

Partial
(CO2 build up)

Bag and bottle with occlusive packing

3. Semi‑closed without absorption.

Yes

No

Bains, modified Jackon Rees, Ayre’s T piece.  Lack, Magill

3. Semi‑closed with absorption.

Yes

Partial

Carbon dioxide absorbers with leak (circle and to and fro)

4. Closed.

Yes

Complete

Carbon dioxide absorbers with no leaks

Open/semi-open circuits (e.g. Chloroform Mask)

Semi-closed circuits (best considered as 'non‑rebreathing' or 'rebreathing')

Mapleson non-rebreathing circuit systems

Table 2. Classification of Mapleson breathing systems.

Class

Location of fresh gas inlet

Valve location

Reservoir bag

Corrugated tubing

Examples & comment

A

Near the bag

Near the patient

Present

Present

Magill, Lack

B

Near to the patient

Near the patient

Present

Present

Obsolete

C

Near to the patient

Near the patient

Present

absent

Obsolete in anesthesia, still used for emergency resuscitation (Ambu-bag)

D

Near to the patient

Away from the patient

Present

Present

Bain

E

Near to the patient

Away from the patient

absent

Present

Ayre’s
T-piece

F

Near to the patient

absent

Present

Present

Jackson Rees

Figure 3. Schematic diagram of the Mapleson classification of circuits.

Rebreathing circuits

Rebreathing circuits and the vaporizer location

Vaporizer out of Circuit (VOC) rebreathing circuits

Circle rebreathing systems with Vaporizer in Circuit (VIC)

Components of the circle system

CO2 absorbent (Sodalime, baralyme)

CO2 + H2O → H2CO3

H2CO3 + 2 NaOH →  Na2CO3 + 2H2O

H2CO3 + 2KOH → K2CO3 + 2H2O

Na2CO3 (or K2CO3) + Ca(OH)2 → 2NaOH (or 2KOH) + CaCO3

Y-piece

Breathing tubes

One-way (unidirectional) valves

Fresh gas inlet

Adjustable pressure limiting valve (Pop-off valve)

Pressure manometer

Rebreathing (Reservoir) bag

Scavenging

Methods of scavenging

Passive scavenging.

Passive with adsorption

Active scavenging

Active scavenging with adsorption

Further References:

  1. Veterinary Anesthesia Hall, Clarke and Trim. WB Saunders 2001

  2. Veterinary Anesthesia Thurmon, Tranquilli and Benson. Williams & Wilkins 1996

  3. Handbook of Veterinary Anesthesia Muir, Skarda, Hubbel.  Mosby 2000

  4. Understanding Anesthesia Equipments, Dorsch and Dorsch Williams & Wilkins 1999


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Oklahoma State University - Center for Veterinary Health Sciences all rights reserved
last updated October 19, 2007
Questions? Comments? Dr. Lyon Lee