Anaesthetic breathing systems

Question 1

Describe the fresh gas flow in rebreathing systems

Answer 1

Must replace the animals metabolic O2 consumption. (approx 10ml/kg/min LA, 5ml/kg/min SA). Higher gas flows to start (expired breath = low IAA conc -> dilution). After dinitrogenation + stabilisation -> reduce to match O2 + IAA uptake.

Question 2

Describe denitrogenation.

Answer 2

In rebreathing systems- start of anaesthesia, patient expires N which can lower circuit O2 to hypoxic levels. Purge through pressure relief value and use high flows for 1st 10-15mins

Question 3

Why must care be taken with using nitrogen oxide in ABSs?

Answer 3

In REBREATHING SYSTEMS ONLY: uptake of O2 and N2O occur at different rates -> hypoxic gas mixtures. MUST measure inspired O2/use high flow rates.

Question 4

Advantages of using rebreathing ABS

Answer 4

Economy of O2 + IAA
Inhaled gases = warm + humidified
Less pollution/explosion risk

Question 5

Disadvantage of using rebreathing ABS

Answer 5

Composition of rebreathed gas unknown unless directly measured

Question 6

List the types of rebreathing ABS

Answer 6

Circle system

To-and-fro system

Question 7

List the types of non-rebreathing ABS

Answer 7

Magill system
Lack
Parallel lack
Ayres' T-piece
Ayres' T-piece w/ Jackson Rees' modification
Bain system

Question 8

Describe the fresh gas flow in breathing systems

Answer 8

High fresh gas flow required to flush CO2 away. Calculated using minute volume: if bag on inspiratory limb = 1x, on exspiratory limb = 2-3x

Question 9

Advantages of using breathing ABS

Answer 9

Inexpensive
Simple- easy to move, sterilise
Rel. rapid changes in IAA flow possible

Question 10

Disadvantages of using breathing ABS

Answer 10

Cumbersome- can accidentally extubate
Mechanical dead space!
Difficult to provide high enough gas flow for LA