Breathing Systems

Question 1

What is the function of a breathing circuit?

Answer 1

To supply oxygen and anaesthetic gas to a patient
To remove carbon dioxide
To facilitate manual ventilation if necessary

Question 2

What types of breathing system are there?

Answer 2

Re-breathing
Incorporate a chemical absorbent to remove the carbon dioxide
E.g. soda lime

Non-rebreathing
Rely on a high gas flow to flush out the patient’s exhaled carbon dioxide

Question 3

Types of Non-rebreathing systems

Answer 3

Classified by Mapleson System
Lack System
Bain System
Ayre’s T Piece

Question 4

Lack System

Answer 4

Modified Mapleson A
>10kg
Parallel system - two tubes
○ Inspiratory - often green)
○ Expiratory - clear)
Adjustable Pressure Limiting (APL) or Expiratory valve and rebreathing bag are situated on the expiratory limb
Fresh gas flow = patient minute volume (1 x MV)
Not good for IPPV
Available in a mini form for animals 2-10kg

Question 5

Bain System

Answer 5

Modified Mapleson D system
Coaxial system (tube within tube)
Inner narrow delivers fresh gas
Wider corrugated conveys gas away from patient to the reservoir bag and expiratory (APL) valve
Popular for IPPV

Question 6

Ayre’s T Piece

Answer 6

Modified Mapleson E System
<10kg
Low resistance system
Twisting of reservoir bag is common an potentially fatal
Flush valve is not recommended due to risk of barotrauma and pneumothorax

Question 7

Types of Rebreathing Systems

Answer 7

Contain CO2 absorbent so lower fresh gas flows used
Circle system
humphrey ADE-circle system

Question 8

Circle system advantages

Answer 8

Conserves heat and moisture and anaesthetic gases
Cost efficient in larger patients
Purpose build infant absorbers for smaller patients

Question 9

Circle system disadvantages

Answer 9

Imparts more resistance to ventilation
Disc material may warp/stick to the valve
Standard circle systems can’t be used in small patients

Question 10

Components of circle system

Answer 10

○ Y piece
○ Breathing tubes (smooth or corrugated)
○ Two unidirectional valves
○ Fresh gas (FG) inlet
○ APL valve
○ Reservoir bag
○ Absorber

The volume of the breathing bag MUST be greater than the patient’s inspiratory capacity

Question 11

What is the absorber in a circle circuit

Answer 11

Usually calcium hydroxide
Soda lime and barium hydroxide lime also possible
indicator incorporated to show activity of soda lime

Question 12

Advantages of Humphrey ADE-Circle system

Answer 12

Combines advantages of Lack, Bain and Ayre’s T piece
Economical for spontaneous breathing patients
Preferable for controlled ventilation and small patients
Possibility of asking on absorbent canister
Easy to clean/sterilise
Easy to operate
Allows manual ventilation
Non-ferrous (MRI)

Question 13

Flow Rate