Breathing Systems

A breathing system is a device that conducts gases such as oxygen and anaesthetic agents to the patient and conducts waste gases such as CO2 away.

• Simple and safe to use
• Delivers the right gas mixture
• Allows all methods of ventilation in all age groups
• Efficient
• Pressure relief
• Sturdy, small and light
• Allows easy removal of waste gases
• Easy to maintain with low running costs

• Fresh Gas connection: Where fresh gases enter the system
• Patient connection: Where the patient is connected to the system
• APL valve (adjustable, pressure limiting valve): Helps control pressure in the system
• Rebreathing/Reservoir bag (Bag or bellows): Stores excess gases for the patient
• Corrugated transparent rubber tubing: Flexible tubing for gas flow
• Waste gas connection: Releases waste gases safely

• Open System (Open Inhalation Method): No reservoir/rebreathing bag is used. A mask like the Schimmelbusch mask is used, providing one effective surface for volatile anaesthetics and some space for confining the anaesthetic vapour.
• Semiopen System: Anaesthetic is administered with air, and the respiratory tract is open to the atmosphere during inspiration and expiration. Some reservoir is created over the mask, but it is mostly open to the atmosphere.
• Semiclosed System: The patient inhales from the continuous flow of gases from the anaesthetic machine, including one reservoir/rebreathing bag.
• Closed System: Anaesthetic gases and vapours are not released into the atmosphere. The same gases are continuously recycled after the absorption of carbon dioxide by soda lime. However, oxygen used in metabolism and gases/vapours utilized in the body or lost need to be supplemented.

Advantages of Closed Systems

• Economy
• Retention of body heat and moisture
• Less pollution
• Less chance of explosion

Disadvantages of Closed Systems

• The circuit should be leak-proof
• Potential for cross-infection
• Dilution of fresh gas mixture
• CO2 absorption may not be adequate

Soda Lime

• Composition:
• Sodium hydroxide: 4%
• Potassium hydroxide: 1%
• Water: 14 to 19%
• Silica (to prevent powdering calcium hydroxide): 95%
• Size: 4 to 8 mesh
• Chemical Neutralization of CO2:

CO2 + H2O → H2CO3

H2CO3 + 2NaOH → Na2CO3 + 2H2O + heat

H2CO3 + Ca(OH)2 → CaCO3 + 2H2O + heat

• Soda lime is pink colored and turns white when it becomes inactive. There is a gain in weight when it is exhausted.
• Trichloroethylene should never be used in a closed circuit with soda lime because toxic products like dichloroacetylene may be formed, which can cause paralysis of cranial nerves, particularly the 5th and 7th.
• With sevoflurane, the production of substance A (vinyl halide) can cause dose-dependent renal damage in rats but has never been seen in humans.

Baralyme

• Composition:
• Barium hydroxide: 20%
• Calcium hydroxide: 80%
• Water bound crystallization
• No silica is needed.

Chemical Neutralization of CO2

• CO2 + H2O → H2CO3
• H2CO3 + Ba(OH)2 → BaCO3 + 2H2O + heat
• H2CO3 + Ca(OH)2 → CaCO3 + 2H2O

Baralyme produces less heat and is less caustic than soda lime.

Circle Breathing System

• Soda lime is usually used in a canister.
• Inspiratory and expiratory tubing are connected to the canister.
• A vaporizer can be incorporated in the back bar of the anaesthetic machine (outside the circle) or on the expiratory limb within the circle.
• Exhaled gases are circulated back to the soda lime canister. After CO2 absorption, the gas joins the fresh gas flow to be delivered to the patient.
• The system can be used for both spontaneous or controlled ventilation.
• Advantages: Efficient.
• Disadvantages: Bulkiness, more resistance, more difficulty in recharging, chance for cross infection.
• Malfunction: Expiratory valve stuck closed, inspiratory valve stuck closed.

Adequate monitoring of inspired oxygen, end-tidal CO2, and inhalation anaesthetic is needed.

Mapleson, a professor of medical physics in Cardiff, published his analysis of the behavior of various combinations of tubing, reservoir bags, and fresh gas flows (FGF) used in breathing systems in 1953. He classified breathing systems as Mapleson A, B, C, D, E, and F. Today, only Mapleson A, D, E, and F, along with some modifications, are commonly used.

What FGF’s are needed?

Mapleson	Systems	Uses	FG-SV	FGF IPPV
A	Magill Lack	Spontaneous General anesthesia	70-100 ml/kg/min	min 3 * MV
B		Very uncommon. Not in use today
C		Resuscitation, Bagging		Min 15 lpm
D	Bain	Spontaeous IPPV, Gen. Anesth	150-200 ml/kg/min	70-100 ml/kg/min
E	Ayre's T Piece	Very uncommon, not in use today
F	Jackson Rees	Pediatric < 25 kg	2.5-3 * MV Min 4 lpm

Mapleson A (Lack) System

The Mapleson A or Lack system is a modification of the Magill system in which the valve is moved to the machine end of the system using an additional length of tubing. This addition of tubing increases the volume of the system and makes it relatively heavy at the patient end.

Key points about the Mapleson A system:

• It is one of the most popular and widely used breathing systems.
• It is not ideal for controlled or assisted ventilation.
• However, it can be used for spontaneous ventilation.
• The fresh gas flow should be approximately equal to the alveolar minute volume (about 10 ml/kg/min).
• It is not considered ideal for pediatric anesthesia.
• Rebreathing of exhaled gases occurs, and it is not suitable for intermittent positive pressure ventilation (IPPV) unless a large fresh gas flow is used.

Mapleson D (Bain) System

The Mapleson D or Bain System is a co-axial system in which the fresh gas is delivered directly to the patient. It requires very high fresh gas flows to prevent rebreathing of carbon dioxide (CO2). This system is highly convenient and is particularly popular, especially for induction, in the UK.

Mapleson F (Jackson Rees Modification)

The Mapleson F or Jackson Rees modification of the Ayres T Piece is a basic system primarily designed for use with very small patients. One significant disadvantage of this system is the inability to remove waste gases safely.

Because it has a bag with an open tail, it is technically considered a Jackson-Rees Modification system.

Mapleson F with APL Valve

Intersurgical decided to modify the Jackson-Rees system by incorporating a closed tail bag and a specially modified APL (adjustable pressure-limiting) valve. This modification allows for the safe removal of waste gases from the system through the APL valve's 30mm outlet.

Mapleson C Bagging System

The Mapleson C is a versatile system that serves multiple purposes in the hospital. It is not limited to anesthesia but can also be found throughout the hospital for various functions:

• Emergency bagging system for resuscitation
• Manual ventilation using oxygen
• Standard induction system in some countries